Delta pandemic and uncertainty

In 1919-20, the second wave of influenza fanned out throughout the world. Although the exact reasons are disputed (mutation, troops coming back home after WW 1), the effect was devastating.

In 2020-21 we have so far experienced two large waves of COVID-19, the original one in February-June 2020 and the second one – fuelled by a combination of a Summer 2020 reopening and the replacement of the original strain by the UK strain, now called Alpha, as well as Brazilian and South African strains (Beta and Gamma).

We are now facing the third (or fourth) wave, cause again by a combination of behavioural changes and Delta strain (and other similar ones). Yet, there is a large uncertainty as to what is likely to happen in the next few weeks, as illustrated below by two consecutive predictions by Scottish Government modellers:

Why is the earlier prediction so dire and the current one a bit better? Why has one week of data made us change the prediction so drastically?

We are in a better situation now, compared to the world in 1919 as well as to the previous waves. But we are also in uncharted territory as we never have seen a massive epidemic growth in highly vaccinated populations (perhaps with exception of measles outbreaks after the mass vaccination drove the numbers down).

The UK is indeed a highly vaccinated country, although not with the highest proportion of fully vaccinated individuals and with a substantial proportion of those vaccinated with AZ which has lower efficacy against Delta variant. Currently, the UK has 50%, Israel 60% and Malta 77% population fully vaccinated, but all three now see an increase in numbers.

But the UK is also carrying out a unique experiment of removing all NPIs while the cases are going up exponentially. As there is no precedence for this strategy, it is difficult to capture all details with the models.

We simply do not know yet how Delta will spread in a highly vaccinated but also highly stratified population. What I mean by “stratified” is that age-limited vaccination created a pocket of susceptibility in school children who are by nature clustered in schools.

At (still) relatively small levels of disease, “stochastic” events like superspreading events are also important and affecting our way to predict. A large group of Scottish fans travelling to a match in London brought the virus back to Scotland. As they mixed together and with other fans, nearly 2,000 reported having caught COVID-19 while at the match.

Epidemiological models by nature are quite sensitive to changes in assumptions. Also, the reproductive number is currently around 1-1.5. This is a region where even very small changes in parameters or assumptions produce large changes in the dynamics. To illustrate this, think about R=1. If R=0.99, the epidemic dies out. If R=1.01, the epidemic grows exponentially; the difference in R is of 1%, but the outcome is very different!

Sensitivity of the epidemic growth in respect to small changes in R.

So to summarise, we are now in a similar situation to weather forecasters facing an unusual weather pattern: We have excellent modelling tools, but our predictions are quite variable. If we want to know the weather on Sunday and check the forecast on Wednesday, we can be predicting blistering heat and sunshine. But on Thursday, the prediction might already be a torrential rainfall.

This lack of predictability, while understandably annoying at times, is also why I love Scotland. But of course, the lack of predictability in COVID-19 can be a matter of life or death.

This is a companion post to an article by Mark McLaughlin from The Times in which he is quoting me. I am indebted to Mark for pointing out the uncertainty in the predictions – and for may stimulating questions.

Vaccine hesitancy and George Washington

There seems to be quite a lot of vaccine hesitancy in the United States, with perhaps as many as 35% of adults projected to refuse the COVID-19 vaccination. One argument is – of course – freedom: Why should the government tell us what to do?

The problem with this argument is that the freedom not to be vaccinated is actually quite a new argument in American history, as Servitje, Lincoln and Yamey tell us in their USA Today piece.

They say:

While some anti-vaccination groups use the term “medical freedom” to reject preventive measures against COVID-19, our nation’s first leaders were strongly committed to public health, including vaccinations. George Washington ordered mass inoculation of his troops against smallpox to secure a victory against the British in the Revolutionary War.

However, Servitje et al make a small error in their – otherwise excellent – article, but actually, the truth is even more staggering. In the otherwise excellent article, Servitje et al do not mention that George Washington did not order his troops vaccinated.

George Washington ordered variolation, a procedure that incurred a much higher risk than Jenner’s vaccine which was not introduced until 1796, whereas Washington’s order came in 1775.

As Gareth Williams writes in his excellent Angel of Death book:

“Smallpox kept George Washington’s unprotected army out of British-occupied Boston and later wiped out the American forces besieging Quebec (…) Washington (another scarred victim of smallpox) subsequently decided to order large-scale variolation of the American forces, which abolished their fear of the disease and was probably decisive in enabling them to chase the British out”

Angel of Death, page 145

Such was a fear of smallpox that even a pretty scary procedure like variolation was preferred to getting ill. Which in no way diminishes Servitje et al argument, as the risks of complications from COVID-19 vaccines are small compared to the risk of variolation which in turn were minuscule compared to smallpox where the fatality rate could be 90% or greater and nearly 100% is observed in cases of early hemorrhagic smallpox.

Erratum: Washington indeed wrote “inoculation” and Servitje et al never say that he referred to vaccination. This has now been taken into account in the text. a blog in Polish

As I have found myself writing an increasing number of articles on coronavirus in Polish, I have created a new blog which is specifically to address misconceptions about the pandemic over in Poland.

All Polish-language posts published on this blog will stay here, but they are also copied to the new blog.

By the way, the picture above (licensed from Shutterstock) depicts a historic old Main Square in Warsaw, with the famous Syrenka (Mermaid) monument in the background, and of course anti-COVID masks in the foreground.