Ernie Dainow's Blog

“Has Omicron peaked?” seems to be the number one news item.

If you look at overall case counts, it looks like the UK has peaked and is declining, following the pattern seen earlier in South Africa. In Canada and the U.S. people are hoping that the same pattern will follow, and soon. 

COVID-19 Data Explorer

Because of the shortage of Covid tests, many people who get Omicron do not get tested and so the number of reported cases is much lower than the true number of people with Covid. Here is the forecast for Canada that takes the unreported cases into account.

CBC National January 14, 2022

The January 4 blog predicted that Omicron would peak towards the end of January at about 125,000 cases and return to pre-Omicron levels at the end of February. The Canada forecast here is similar but with a sharper and more rapid peak and decline by the end of January.

If this forecast holds true, it does not mean the crisis will be over by the end of January. Hospitalizations and deaths lag the case counts by a few weeks. There has just been a sharp increase in ICU cases and deaths.

CBC National Jan 10, 2022

There was another informative email from Dr. Andrew Morris this week. If you haven’t read it, here are some of the key points.

– in previous waves we have seen “false peaks” where it looked like a peak was achieved, when really it was a temporary decline that preceded another increase in cases.

-people in Canada will unnecessarily suffer more from Covid because of a shortage of therapeutic agents (medicines that have been approved for treating people who are sick with Covid). We suffer from insufficient production, insufficient procurement, poor coordination, delayed approvals and mismanagement by some provincial officials.

– one reason Ontario hospitals are struggling is because it has very few hospital beds per capita.

Masks

Because Omicron is so much more transmissible than previous variants, it is highly recommended that people use an N95 or KN95 mask. These masks are almost twice as effective as the more widely used surgical masks or cloth masks. 

However, a lot of K/N95 masks that are being sold, even from reputable sources, do not meet the standard of filtering 95% of particles. The following report shows the test results of many masks being sold.

Lab tests of K/N95 masks

The K/N95 masks generally make it harder to breathe and may be uncomfortable if you need to wear it for a long period of time. I initially used a N95 mask that had two ties that go over the head. I found this very awkward because it was difficult to undo enough of the mask to take a drink of water or wipe your nose. I switched to a KN95 mask that has ear loops which I found to be more flexible and also more comfortable. 

Here is a good report on How to find the right Covid mask (and avoid counterfeits).

If you find that you just can’t wear a K/N95, you can improve the fit of a surgical mask by folding it according to these instructions.

How to Knot and Tuck Your Mask to Improve Fit

Is Covid becoming Endemic?

More and more people are talking about herd immunity or the pandemic becoming endemic after the Omicron wave. This is all conjecture. I haven’t seen any science. Here is a way to estimate this. 

1. Using the basic epidemiological model with an estimate of R₀ = 10.0 for Omicron, herd immunity is reached when immunity of the population is at least 90%.

Herd immunity

2. Canada’s vaccination rate is currently 78% of the whole population. Not many of the remaining unvaccinated people are likely to get vaccinated. After numerous campaigns, vaccine mandates and various other incentives, most of the unvaccinated are pretty firm in their position.
Tracking the spread of the coronavirus in Canada

3. The number of people who have been infected with Covid and received natural immunity is currently about 3 million. Adding in an estimate for the uncounted cases during the Omicron wave will increase this to about 5 million, or 13% of Canada’s population.

4. The total immunity in Canada after the Omicron wave will be 78% + 13% = 91%. This is on the border for herd immunity.

However, because of increasing breakthrough infections in people who have been vaccinated, the effective level of immunity will be less than 91%.

It remains to be seen if Omicron is the last wave, but even if it is, many people will continue to get sick and die from Covid. This is an endemic state, similar to influenza. In 2018-2019, before the coronavirus pandemic, there were 10,000 cases of flu per week in Canada during the winter peak. 

Annual Flu Report Canada

Since the major mode of transmission of the coronavirus is between people who are in proximity to each other, it seems intuitive that in societies where there are more crowded living conditions there would be more spread of Covid-19. Since the first days of the pandemic, people have suggested that the virus was spreading more rapidly in areas and countries that were more densely populated.

However this article, in a widely read usually responsible newspaper, argues that the relationship between population density and the spread of Covid-19 is a “myth” and has been “debunked”.
Stop Blaming COVID-19 Deaths On Population Density

While there are quite a number of good arguments here, this is a classic case of someone forming his own conjecture without reading the science. I don’t think the reporter who wrote this article reviewed any of the many scientific studies that examined this question. This is a really good example of people who “do my own research” instead of studying the actual science. This lazy approach has been a big reason there has been so much misinformation circulated about the pandemic. It’s not easy to read some of the science. Published papers are long and dense with a lot of detail and you need to have some understanding of statistics to understand the research and the results. Read this for example.
Temperature and population density influence SARS-CoV-2 transmission

The Huffpost reporter argues quite well that there are many reasons to explain the spread of Covid, such as 
– public health policy
– residential overcrowding (which is not the same as population density)
– work environments which increase the frequency of face-to-face interactions 

But this does not mean that population density is not an important factor. There are many factors that affect the spread of a respiratory illness.

It does seem true that there does not seem to be a connection between Covid and population density at the country level. If Covid increased with population density, the data points on this chart. would form a line rising from left to right.

https://ourworldindata.org/grapher/covid-19-death-rate-vs-population-density?yScale=linear&minPopulationFilter=1000000

But when you look at a more granular level, at smaller regions within a country, there does seem to be a very strong relationship. There have been a number of statistical studies to try and analyze this more completely. One of the better papers concludes that

Population density and temperature are drivers of R0 at state level in the United States (p<0.001), but the effect of lockdown is greater.

See Table 1 in Temperature and population density influence SARS-CoV-2 transmission

The additional conclusion about temperature is that as temperature increases Covid cases decrease. This has been widely noted by epidemiologists who have pointed out that in winter, people congregate indoors more than in summer and this is an important factor that gives rise to the spread of all respiratory illnesses such as seasonal flu.

It’s pretty easy to see that population density drives Covid cases yourself. Charts on the next few pages show it for the U.S. and Europe. If you look at the Covid hot spots on the first map, it is usually an area of high population density on the second map.

U.S. Covid hot spots Jan 4, 2022

https://www.nytimes.com/interactive/2021/us/covid-cases.html

https://www.nicepng.com/ourpic/u2q8u2e6t4i1y3e6_us-population-heat-map-stylish-decoration-population-united

Europe Covid hot spots Nov 24, 2021

https://www.nytimes.com/interactive/2021/11/30/world/europe/europe-covid-surge-omicron.html

https://www.eea.europa.eu/data-and-maps/figures/population-density-1992

New Year arrived with a bang, an explosion of coronavirus across Canada and the U.S. 

COVID-19 Data Explorer – Our World in Data

People reporting on TV, from politicians to public health scientists, seemed to be alarmed and a bit surprised. They shouldn’t be. Shortly after South Africa reported the new variant Omicron at the end of November, they provided statistics that showed that the number of cases was doubling every 2-3 days. This is really simple math. You don’t need a sophisticated epidemiological model, you don’t even need a calculator to see the impact of this over a few weeks. If 4 people with Omicron arrived in Canada from South Africa before the variant was identified, those 4 cases could have spread to 32,000 people by January 1, 2022, which is roughly what the latest case count is for Canada.

There were early reports from South Africa that Omicron is less severe than Delta. But the population profile in South Africa is a lot younger than the UK, Canada and the U.S. It was not so clear that this pattern of milder infections would be true for older people who have been a lot more vulnerable to the previous strains of the coronavirus.

On Dec 22, a careful study was published by Neil Ferguson and his team at the Imperial College London. He is one of the pre-eminent epidemiologists in the world. The analysis controlled for many variables such as age and sex and concluded that the reduction in the risk of hospitalisation for Omicron relative to Delta was 40-45%. This now seems to be an accepted characteristic of Omicron.
https://www.imperial.ac.uk/mrc-global-infectious-disease-analysis/covid-19/report-50-severity-omicron/

But even if the probability of hospitalization is lower, when there are so many more cases than Delta, there may be an overall increase in hospitalizations. In fact, patient admissions to hospitals have now started to increase sharply.

COVID-19 Data Explorer – Our World in Data

This is what is alarming many public health officials. This trend could overrun the health care system. So, many regions are re-introducing social controls. While most governments are insisting that “lockdowns” are a thing of the past, in fact what we are seeing now is “creeping lockdowns”.

One thing that does not seem to be reported very clearly is how long this wave will last. In South Africa it seems that it peaked quite quickly and is coming down (see first graph) but that does not mean it will happen here.

To try and answer this question, I updated my coronavirus model for the Omicron variant with the following assumptions:
1. By January 9, Omicron will account for 90% of the coronavirus cases in Canada.
2. Omicron is 4 times as transmissible as Delta.

Based on this, it does look like the Omicron wave will peak more quickly and decline more quickly than the earlier waves. The peak is towards the end of January with cases returning to pre-Omicron levels at the end of February. What determines when the decline begins is when the total immunity based on both vaccinations and natural immunity from people who have had Covid reaches a critical threshold. This model is very sensitive to the assumptions, so the peak cases may be more or less than 100,000 depending on how effective the various new restrictions are in reducing social interactions and transmission of the virus.

One thing that some epidemiologists are saying is that almost everyone will get Omicron, even vaccinated people. I don’t see anything like this. The total number of people in Canada who had Covid-19 at the end of the Omicron wave in the model, both symptomatic and asymptomatic, is about 8 million people out of a total population of 37 million. So about 30 million people will not get Covid because they are being protected by the vaccine, in spite of many breakthrough cases. So it does not make sense from a health perspective to surrender, throw caution to the wind and not worry about getting infected because “everyone will get it anyway”. It’s hard to predict if you will have a mild case or not. In addition, very little is known at this point what the effect of Omicron is on “long covid”. With earlier variants, 5% of people who were infected have lingering symptoms for many months and in some cases much longer.
What is my risk of getting Long Covid

The other thing some epidemiologists are saying is that this may be the last wave of the pandemic after which Covid will become endemic. It won’t disappear and will continue to infect people, but not at an epidemic rate, and will become more like a seasonal flu. However Dr. Fauci commented that most pandemics in the past have subsided after two waves, but Covid-19 has been unprecedented and has now proceeded to a fourth wave. So the most experienced experts in the field are really not able to predict what will happen. And the threat of another variant after Omicron is of course still possible.

The news has been full of reports of the Covid-19 Omicron ever since it was declared a variant of concern by the World Health Organization (WHO) on November 26, 2021. There has been a lot of new information every day and many changes to some of the earlier reports. The following is an excellent summary and assessment that is complete and up-to-date to December 18. Dr Andrew Morris is a professor of Infectious Diseases at the University of Toronto and a member of the Ontario COVID-19 Science Advisory Table. It is worth reading all of this and perhaps signing up for his regular mailings.

See Email#77 in Covid Emails

Here are some of the important highlights.

• The early data from South Africa suggested that Omicron might be less severe than Delta because hospitalizations from Omicron were less frequent than Delta but this is not being borne out in Denmark, and probably will not be true in Canada and the U.S.
• There are several other reasons why the progress of Omicron in South Africa may be very different than here. 
• Omicron is spreading rapidly around the world. Besides South Africa, UK, and Denmark, there are  steep Covid case increases in Norway, France and Spain.

What should you do?

Besides the recommendations made by Dr Morris in the article above, you should make sure you are using an effective mask. The typical surgical mask is only about 50% effective because it is not very tight fitting and there is a lot of space where virus particles in the air can get through to your mouth and nose. An N95 mask on the other hand is 95% effective. Cloth masks shouldn’t be used at all. 

One reason that Omicron may be so much more transmissible than Delta may be because it spreads more readily through the air. This could be because people who have Omicron may be expelling larger amounts of virus particles than with Delta or it could also be that the aerosol particles may be smaller, circulate more quickly and stay in the air longer. The evidence now suggests that Covid-19 is primarily spread through infectious aerosols that people breathe in.
Preliminary data hint at what makes Omicron spread so readily.

The previous blog article highlighted how ventilation is a big risk because there are no standards, from small spaces like restaurants to large spaces like factories and warehouses. Ventilation is very important for removing the small aerosol particles in the air. The larger droplets that contain the virus tend to drop out of the air within 6 feet shortly after being exhaled. Social distancing in enclosed spaces is not enough to keep you safe; the virus aerosol particles which may circulate in the air for hours may be more dangerous than the droplets.

It is difficult to assess how well a space is ventilated without some measurement or getting a statement about the HVAC system from the building management. And you cannot assume that a newer building will be better ventilated than an older building. 
Air Circulation and Coronavirus: How to Judge a Ventilation System

You can judge if a space is small relative to the number of people in it. So a crowded restaurant with low ceilings is probably not very safe whereas a gym with high ceilings that is not very crowded may be a lot safer. On the other hand, you could get infected in an empty restaurant from aerosol particles that are still circulating from a patron who left hours before you arrived. 

Finally remember that the best way to protect yourself from Covid infection is having several layers of defense. The following illustrates this well. 

At the end of September the 4th coronavirus wave peaked and began to decline. With increasing vaccination rates it was widely assumed that this was the last big wave of the pandemic in Canada and the US. However, in recent weeks case counts have plateaued and started moving up. Is this the start of a 5th wave?

Here is the projection for Ontario from the Covid-19 Science Advisory Table.

Here are the Covid cases for different regions in the U.S.

What happened?

One thing that happened is the emergence of new variants. The Delta Plus variant AY.4.2 may be slightly more transmissible than the Delta variant. It has made headway in the UK, outcompeting the Delta variant and now accounts for about 10% of sequenced virus samples there. To date it has not been widely reported in the U.S. or Canada.

Emergence of the ‘Delta Plus’ coronavirus variant

However, in Canada, some other Delta variants have been identified, AY.25 and AY.27. In Saskatchewan, AY.25 is becoming the predominant circulating strain, more than 50% of all cases. In Ontario, AY.25 accounted for 31% of confirmed cases.

What we know about Delta’s newest variants

This chart shows the spread of AY.25 and AY.27 in Saskatchewan.

In various parts of Europe there has been a sharp increase in Covid cases. Germany, which managed the pandemic better than most other countries (except Scandinavia) has more cases and hospital admissions than at any other time during the pandemic.

COVID-19 Data Explorer

The extent of the new Delta variants in Europe is not known. The most likely causes for the spike in cases are low vaccine uptake, waning immunity among people inoculated early and growing complacency about masks and distancing after governments relaxed curbs over the summer.

Why is Europe returning to the dark days of Covid?

What should be done?

Here is an assessment from a respected epidemiologist Dr. Colin Furness. He points out a number of “dumb” things that Ontario has done and how they should be corrected.

Allowing full stadium attendance was a sure way to allow further spread. This should be rolled back.

Restaurants are “one of the most dangerous places to be” because there are no regulations or standards for air filtration. The Ontario government has not officially acknowledged airborne transmission of the coronavirus. This will probably not be done by conservative governments in general because it would imply updating their health and safety standards to require many businesses from large warehouses to restaurants to incur the expense of upgrading their heating and cooling systems. However, requiring HEPA filters in spaces where large numbers of people are congregating is really fundamental to controlling the spread of the Delta virus and its variants. 

What is the likely outcome?

It was not possible to update the spreadsheet model because there are too many unknowns about the rate of spread and the effect of the new Delta variants. If these new variants do not spread more than 15% more rapidly than the Delta variant and if vaccinations continue to increase, especially now that the vaccine has been approved for children, my expectation is that in Canada and most regions of the U.S. the current increase in cases will be more of a bump than a 5th wave. However in low vaccination areas such as the American South and parts of Europe, the balance could be the reverse and they will experience a full 5th Wave.

I have noted numerous times how inept Public Health has been in handling the Covid-19 pandemic and the many mistakes that they made. But I was not able to explain in more than general terms why there were so many errors and what was wrong with the system. I have just finished reading an incredible book which explains a lot of this. It documents the many things that happened behind the scenes in the pandemic in the U.S. It tells the stories of many unsung heroes who really made a difference in overcoming the shortcomings of Public Health.

The book is The Premonition by Michael Lewis, published in May 2021. Here are a few of the surprising things that Lewis explained.

The bungled response in the US to the pandemic was not due to Donald Trump. There were many more failures in the system than all the outlandish statements and directives from Trump. Chief among them was the CDC. In many cases the CDC did not act when it should have and in some cases actually hindered some people in the public health system who were trying to contain epidemics, not just for Covid-19 but also earlier public health outbreaks.

The other surprising thing is that George W. Bush was the one who first developed a pandemic plan for the U.S. In 2005 someone gave him a book called The Great Influenza about the 1918 pandemic. There was a document from the Department of Health that laid out pandemic plans to speed up the production of vaccines and stockpile antiviral drugs. Bush said “This is bullshit. We need a whole society plan.” The disaster of 9/11 was still fresh in his mind and so he created a task force to create a comprehensive strategy for dealing with a pandemic.

The task force was interested in computational models that could predict pandemic spread. There were some academic models available but they were complicated, unwieldy and slow. Through an unusual sequence of events, they came across a usable model that had been developed by a 13 year old girl for a science fair and later refined by her father who was a researcher at Sandia National Labs.

Among all the incredible individuals and stories that Lewis uncovered, one person more than any other could be considered the hero. Charity Dean was a public health nurse working in California at the county level. She had a knack for seeing public health risks and had made some bold decisions to contain several infectious disease outbreaks, such as meningitis and tuberculosis. She was noticed and promoted to assistant director of the California Department of Public Health in 2018. 

When she saw the reports coming out of Wuhan in December and January 2020, she did some research and became very concerned. But when she tried to inform her boss, she was told not to use the word pandemic because it might alarm people. In the absence of direction from either the Whie House or the CDC,  she continued to try to press her case but she was barred from many meetings. Eventually, at the risk of being fired, she intruded on some meetings and her analysis and concerns eventually reached Governor Gavin Newsom. It was her interventions more than anything else that led California to issue a stay-at-home order in March 2020. This was the first state to take such action and it influenced many other states to do the same.

In this short excerpt from an interview, Lewis describes what he wanted to accomplish with this book.

In a more extensive interview Lewis describes the ‘ignored characters’ of the pandemic and why their premonitions were pushed aside.

Here is a more complete book review of The Premonition.

But I don’t think there is any substitute for reading the full book. Lewis is an incredible researcher and writer and there are many fascinating things that are not covered in any interview or reviews. Several previous books by Lewis have been made into blockbuster films.

Moneyball

The Big Short

On the back cover of The Premonition there is this quote from a book review.

I cannot imagine higher praise for an author than this. If Lewis wrote a history of the stapler, I would read it too.

The first blog article on the Delta variant, on June 18, 2021, showed an increase in cases in July but declining throughout August and beyond. This was more of a bump than a fourth wave.
https://anydaynow.blog/delta-variant/

The blog on July 19 revised the model projections by recalculating herd immunity for the delta variant when 80% of the population was fully vaccinated. Then vaccination rates were projected and herd immunity was predicted in August in Canada.
https://anydaynow.blog/herd-immunity-recalculated/

But here we are at the end of August and daily cases in Canada are still increasing.

What happened to herd immunity?

The big change was that at the beginning of August, the rate of vaccination decreased in Canada. On the current trajectory, 80% fully vaccinated will not be reached until October instead of August.

https://tinyurl.com/bn353kvy

This change results in a fourth wave that peaks with about 6,000 new cases per day at the beginning of October, 2021. After that, cases decline to a negligible amount.

It’s amazing how many people have became experts in public health in less than a year. Many of these people, like state governors and provincial premiers, use their newfound knowledge to make major decisions that affect the health of millions of people. Professionals working in the field of public health generally have at least six years of training, for a medical degree and/or a master’s degree in public health. Does anyone believe that politicians are so much smarter than health professionals that they can become experts in a year?

Public Health covers a very wide range of areas, from managing and monitoring disease to biosafety and security.
https://www.canada.ca/en/public-health.html

Contrary to what some people might think, public health did not just evolve in the last year with the onset of the coronavirus pandemic. Public Health has been an evolving scientific discipline for a long time.

Lockdown and other social distancing measures are not unique to the coronavirus pandemic. There are many articles and books about how plagues were dealt with in the past.

“From the onset of the Black Death in 1347-48, Italian cities which faced the Mediterranean, an epidemic sea, constructed a complex and articulated health defence system which was an example to all other western countries. The cornerstones of this health defence system lay in quarantine, sanitary cordons, lazarets, disinfection, and in the social regulation of the population at risk.”
https://pubmed.ncbi.nlm.nih.gov/19227587/

“Popular narratives continually included grievances about the cruelty and inequity of quarantine and the militaristic nature of its implementation. Despite these objections, quarantine remained a staple of the government response to plague outbreaks throughout the seventeenth century.”
https://pubmed.ncbi.nlm.nih.gov/22611587/

The Public Health Act in Britain was passed in 1848. It aimed to improve the sanitary condition of towns in England and Wales by placing the supply of water, sewerage, drainage, cleansing and paving under a single local body with the General Board of Health.

The Vaccination Act 1853 introduced compulsory smallpox vaccination in England and Wales.

The Infectious Disease (Notification) Act 1889 mandated the reporting of infectious diseases to the local sanitary authority, which could then pursue measures such as the removal of the patient to hospital and the disinfection of homes and properties.

The first public health organization in the U.S. was in New York City in 1866.

https://en.wikipedia.org/wiki/Public_health#After_the_18th_century

In 1905 the U.S. Supreme Court upheld the legitimacy of compulsory vaccination in Jacobson vs. Massachusetts. The Court compared the right to enact public health measures during an epidemic to the right of a government to defend its people from a military invasion. They compared the right to compel individuals to be vaccinated, whether they wanted to or not, to the power to conscript people to raise an army. This remains the major case in public health law today.
https://www.brandeis.edu/now/2020/may/smallpox-and-coronavirus-willrich.html

The current controversy raging over mandating vaccination for Covid-19 is at odds with long-standing principles encased in law going back over 100 years.

Why is there a debate over vaccine mandates? 

The various measures being proposed to mandate vaccinations are not compulsory orders requiring people to get vaccinated. They are just simple rules made for public health, that in specified areas, unvaccinated people pose a health risk to other vaccinated people in that space, and so unvaccinated people are to be restricted from entering that space. The space may be hospitals, restaurants, stores, or offices under the jurisdiction of a particular health authority. Such decisions are clearly within the bounds of public health authority.

Private companies also have the right to ban unvaccinated employees from the workplace for the safety of their employees. Many American companies, including those operating in Canada, require a medical exam as part of a job application. The information is not given to the employee but is used by the employer in any way they wish and may be used to deny employment.

One reason there is so much debate over vaccine mandates is that many public health officials have not taken initiative and leadership throughout the pandemic. Many have been working in a government bureaucracy for their whole career and they did not step forward when the pandemic was recognized to insist on instituting public health measures, even though that is supposed to be an important part of their job. They continually deferred to the political leaders, even when those leaders made bad public health decisions. A good example of this was David Williams, the chief medical officer of Ontario. He was a typical dry bureaucrat with little foresight or initiative and rarely challenged decisions made by Premier Doug Ford. In spite of criticisms and calls for him to resign, from many parts of the medical and public health community, Ford reappointed him for another term. However, shortly after starting his term, Williams finally saw the light and announced he would retire in June 2021.
https://www.cbc.ca/news/canada/toronto/ontario-top-doctor-pandemic-retirement-1.6046068

Only in extreme cases have public health officials overridden bad decisions made by politicians. One case of this was when Premier Ford in Ontario was very slow to bring in measures to control the large spike of the third wave. In response, the City of Toronto’s medical officer of health issued an order to close the schools, even though the Ontario Education Minister said the provincial government believed schools were safe and not sources of transmission of Covid-19.
https://www.cbc.ca/news/canada/toronto/toronto-closing-schools-covid-19-1.5976923

What should have been done?

If more public health officials had just done their job and issued orders to protect public health, without deliberating and knuckling under political pressure, a lot of bad decisions made in managing the pandemic could have been avoided. 

Restricting unvaccinated people from public places, such as hospitals, airplanes, trains, restaurants, shopping and office buildings where they are a health threat to others is just good public health practice, nothing more. The debate over requiring medical workers to be vaccinated is particularly ludicrous – people who go into a hospital for medical treatment should not be exposed to an increased risk of getting Covid-19. This has nothing to do with “personal freedom of choice”, it is fundamental public health where the health of the public is being protected. 

It is clear that a lot of people from citizens to people in power do not really understand what public health is and don’t feel it is an obligation and a priority of society, even though it is science that has been developed for hundreds of years and has corresponding laws that can be enacted by public health officials when necessary.

People who are demonstrating against vaccine mandates do not oppose the government requiring them to get a license to drive a motor vehicle. It is the law, and the purpose of the law is to protect innocent people from being injured by drivers who do not have adequate vision or safe driving skills. The purpose of public health is exactly the same – to protect innocent people from getting infected with a serious illness by people who are carriers of the disease.

In May, the blog showed that Covid-19 has a Herd Immunity threshold of 60%-75%. In other words, 60%-75% of the population must have immunity (from prior infection and vaccination) to prevent epidemic spread of the disease.

This was based on R₀, the basic reproduction number, being 2.5 for Covid-19 (green bar on this graph).

With the increase of the Alpha and Delta variants becoming the major coronaviruses in many countries, including the UK, Canada and the U.S., this has now changed.

The Alpha variant is 1.5 times more transmissible than the initial coronavirus.
The Delta  variant is 1.6 times more transmissible than the Alpha variant.

This increases R₀ to 2.5 x 1.5 x 1.6 = 6.0

Reading up from 6.0 on the horizontal axis of the graph we get a Herd Immunity threshold of .85. This means that 85% of the population needs to be immune. This is a big part of the explanation for the sudden spike in cases in the UK and the U.S.

https://tinyurl.com/76t5h6vn

The other part of the explanation is that while single vaccination rates went up sufficiently to protect against the Alpha variant, protection against the Delta variant really requires full vaccination. The immunity level of fully vaccinated people has not reached the 85% level in any of these countries. Add 10% to the numbers in the following graph to include people with immunity from prior Covid-19 infections to get the total immunity level for the population.

https://tinyurl.com/bn353kvy

The other big problem is that as the number of people vaccinated increases, there is a slower vaccination rate. People with vaccine hesitancy make up a larger proportion of the people who are unvaccinated. The graph above shows this as a decrease in the slope of the line. This has occurred in the UK and very significantly in the U.S. since mid-May. Canada does not show this slowdown yet.

A simple projection of the above chart, assuming these countries maintain their current vaccination rate, shows the following results for reaching herd immunity when about 80% of the population is fully vaccinated:

Canada in August
UK in November
U.S. in January 2022

Covid-Zero is a strategy to impose a range of restrictions including strict lockdowns and rigorous testing and tracing to drive transmission of Covid-19 to zero. Several organizations have been set up to promote this strategy to end the coronavirus around the world.
EndCoronavirus.org

It has had remarkable success in a number of countries, such as Australia, Vietnam, Taiwan and New Zealand.
Get Real Canada, Get to Zero

However, Australia’s success with Covid-Zero seems to have run into a roadblock. It seems like the Delta variant spreads too quickly for this strategy to continue working. Who would have predicted this a few months ago?
Why the Delta Variant Could End Australia’s Pursuit of ‘Covid Zero’

Many countries in Asia who have also done really well keeping Covid cases low are running into the same turn of events.
As Delta Variant Surges, Outbreaks Return in Many Parts of the World