Vaccinating Essential Workers

After many long months with no treatment or vaccine available, and widespread social distancing the main tool for fighting the pandemic, there are now four different vaccines approved that are effective for COVID-19. Phase 3 trial data and experiences since then show that the Pfizer and Moderna vaccines are safe and highly effective at preventing disease. Even better, preliminary results point to them also being effective at preventing infection, which means they will block transmission of the virus. Vaccination of the majority of British Columbians will be the backbone of our recovery from the pandemic.

Unfortunately, we will not have enough vaccine doses for every British Columbian who wants to be vaccinated before the end of summer. We have to decide in what order British Columbians get the doses we do have. We hope that soon, people 80 years and older, COVID-facing healthcare workers, and remote indigenous communities will have all received both doses. We need to figure out who comes next.

One well-known fact about COVID is that older age groups have the highest risk of experiencing severe complications or dying from being infected. So you might think that the best thing to do is vaccinate people in descending order of age, in order to minimize the harm. This works if everyone is equally likely to be exposed to the virus – but they aren’t.

Another approach is to target essential workers: the people we depend on to keep things running, and who have contacts with lots of other people as an essential part of their job. They include teachers, taxi drivers, retail workers, food production workers, law enforcement, public safety, first responders, social workers, workers in agriculture and transportation, and many more. Essential workers are on the front line: we are asking them to take a much higher risk that they will be exposed. And if they are infected, they risk infecting many others.

But if they are vaccinated, there will be less COVID around and therefore less exposure to the virus for everybody else, including older people.

In our most recent preprint we present the results of our mathematical modeling of the COVID vaccine rollout in BC, using data on how the vaccine impacts infection, transmission and symptomatic disease. Our simulations strongly suggest that it is better for everyone if we vaccinate essential workers once those who are 80 and older are vaccinated. This may seem counterintuitive, so we’ll explain why we think it is the best strategy for BC, and may not be the best strategy in other places.

One important consideration is that although the vaccines are very effective, they are not perfect, and perhaps as many as 5-10% of people who get both doses of the vaccine will not be protected. In addition, perhaps 15% of people will decline the vaccine. This leaves around 20-25% of the elderly not protected. So even if we devoted all our vaccine resources to the elderly they will not be completely protected. We will need to use other measures to prevent many hospitalizations and deaths.

On the other hand, by vaccinating younger people with many contacts we can greatly reduce the amount of virus in the population. This will mean that very few elderly people are ever exposed to the virus. Fewer exposures means many fewer infections among the elderly, whether they have been vaccinated or not.

Whether protection through vaccinating older people first is more effective than preventing exposure by vaccinating younger essential workers depends on many factors which are best captured in simulations. Our simulations of BC found that vaccinating essential workers early, rather than vaccinating the population in decreasing order of age would lead to up to

• 200,000 fewer infections
• 600 fewer deaths
• $230 million decrease in healthcare costs

The reason for this is that in BC we have been partially successful in controlling the spread of the virus with social distancing and other measures. It is not inevitable that the majority of British Columbians, and in particular the elderly, will be exposed to the virus. The reduction in transmission brought about by vaccinating essential workers, those who cannot distance as part of their job, is highly effective for reducing COVID rates province-wide, and it is well worth it to reduce risk to the elderly, along with leading to many fewer infections, and reduced health care costs. (Note: the above numbers come from comparing to a situation where the reproduction number R - accounting for distancing measures - is 1.3 after we finish vaccinating those over 80. If it is held lower than that by long-term distancing measures and/or getting control over higher-transmission variants, these numbers would be lower. But keeping distancing measures in place long term has costs too. We model an overall 97.5% efficacy against disease, including prevention of infection and prevention of disease given infection).

Throughout the pandemic we have mostly seen data on cases (infections), hospitalizations and deaths. But there are other consequences to having COVID-19. In our study we also considered chronic disease resulting from COVID infection. One form of this is so-called “Long COVID”, where the symptoms of COVID last for weeks, months, or potentially longer. There are also possible COVID complications: other chronic health conditions caused by COVID, including diabetes, organ damage, and neurological and psychiatric disorders. It’s unclear how common these serious health outcomes are for people who have had COVID, but we used the best available data to estimate how often they might occur, in different vaccination strategies. We found again that vaccinating essential workers earlier can lead to a profound reduction in the number of cases of these long-lasting and damaging conditions.

In contrast, in a region where case numbers are growing fast – fast enough to have 40,000 incident cases per day in BC compared to our maximum ever of about 1000 – the difference obtained by vaccinating essential workers is not enough. Whatever is done, most older people will be exposed, and therefore the best outcomes are obtained by vaccinating in decreasing order of age. But fortunately we have not reached that stage yet in BC, and vaccinating essential workers early will keep more British Columbians safe.

The preprint is posted here and the code is available at the github repository here.