Preparing for an imminent vaccine

News from Pfizer gives hope. What should we do with it?

Welcome to Plugging the Gap (my email newsletter about Covid-19 and its economics). In case you don’t know me, I’m an economist and professor at the University of Toronto. I have written lots of books including, most recently, on Covid-19. You can follow me on Twitter (@joshgans) or subscribe to this email newsletter here.

Contrary to expectations that we have worked hard mentally adjusting to, 2020 looks like it might end on an optimistic note. Yesterday’s news that Pfizer working with the startup BioNTech have Stage 3 trial results on their mRNA vaccine with 90% efficacy is well above expectations. Regulators had been willing to consider vaccines with just 50% efficacy for emergency use authorisation. 90% puts this at the very top of vaccine performance. Only 1 in 10 of those who have received the vaccine were not protected. The flu vaccine many of us dutifully take is often half as effective.

Previously, I have raised concerned about efficacy, distribution and long term impacts of vaccines. The 90% figure goes a long way towards mitigating efficacy concerns. Moreover, mRNA vaccines that both Pfizer and the startup, Moderna, have been developing have a significant distribution advantage. Rather than having to be grown inside, say, chicken eggs, these vaccines can be manufactured. The following video helps explain why.

For this reason, these companies have already been manufacturing vaccine doses ahead of any regulatory approval. This is very valuable from a social perspective. In the US, for instance, each day without a vaccine costs $10 billion and 1,000 lives. We want to push to bring the end of the pandemic earlier day by day.

I am not in a position to evaluate whether these numbers will stick. Will the vaccine ultimately be 90% effective, with whom and will there still be no significant side-effects, also with whom? But in the spirit of optimism, let’s take the news at face value and ask: now what?

The big question is who to prioritise giving the vaccine? Doses will be limited even if the timeline for distribution is the next 6-12 months worldwide. It is fairly obvious that essential workers should be first in line. Not only do they need to be protected but they are also interacting with others so if the vaccine can assist in mitigating viral spread, you get two for one with them.

The tougher questions arise with respect to non-essential workers and others. Broadly speaking we have two groups. We have the vulnerable (older) members of the population who are (a) more susceptible to Covid complications and (b) less likely to be socially active and the less vulnerable (younger) members of the population for which the reverse is true. The usual principles of vaccine allocation start with the vulnerable and then move on to the others. However, those are rules drawn up for the flu vaccine. For a pandemic which is wrecking considerable damage, we are interested in not only protection but also a speedy end to the pandemic. The latter goal drives you to vaccinate those more active so as to slow down viral spread quickly — so long as the vaccine can do that which is the usual presumption. Even for the flu, previous studies had demonstrated that this could actually be more protective of the vulnerable than directly vaccinating the vulnerable.

According to this paper from University of Washington researchers, which group should be prioritised depends on how efficacious a vaccine is. When a vaccine is not very efficacious, then it will do little to mitigate spread amongst active people but can significantly reduce the health risks to the vulnerable, so you should prioritise them. But there comes a point in efficacy where the reverse is true. A very efficacious vaccine can reduce viral spread quickly if it is given to those responsible for spreading first. The results are here:

The case of interest is where the vaccine has 90% efficacy in the lower right corner. Notice that it all depends on what share of the population you can vaccinate. Let’s suppose that in 6 months, you can vaccinate half of the population. In that case, it makes sense to vaccinate those under 50 before those over 50. This is because if you can vaccinate widely enough with an efficacious vaccine, you can suppress the virus and protect others. This is even more desirable if you predict that there will be fewer side effects amongst the young.

Note that this also suggests that you commit to that strategy. You may be tempted to distribute your vaccines amongst both groups. But here vaccinating an older person rather than a younger person reduces the overall health benefits.

There is more to this than I can possibly convey in a single newsletter. But the take-a-way is that we need to consider this carefully. The study suggests that we could have 30% fewer deaths from an optimised vaccine distribution plan than something that is ad hoc. Those are big numbers. We need a plan.

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