So, OK, let’s talk about those blood clots. Freeman’s group put together a bunch of infographics that weaved a few of these threads into a useful tapestry. Instead of comparing the risk of getting Covid to the risk of getting vaccinated—an apples-to-oranges problem—they instead published a document comparing the potential blood-clot risk of the AstraZeneca vaccine to its actual benefit, the number of Covid-related intensive care unit admissions prevented by its use. And then they diced that up by age group and exposure risk. (In real life, exposure risk would differ from country to country and even across professions … and the group assumed 80% efficacy for the vaccine across the board, a necessary simplification … and they used a fixed time span of 16 weeks, because all of these risks shift over time as infection rates wax and wane. Statistics!)

In 100,000 people with low exposure risk, they calculated, the AstraZeneca vaccine might be expected to cause 1.1 people to get blood clots and prevent just 0.8 ICU admissions. If you’re an only-looking-out-for-number-one sort of person, that looks like a reason to avoid the AstraZeneca vaccine—and indeed, European regulators have limited its use. Lucky there’s all those other vaccines.

At the other extreme, among people who for some reason have a high exposure risk—lots of infection running rampant in their county, say—in the 60-to-69 age bracket, the vaccine might cause just 0.2 cases of blood clots (which seem mostly to affect younger people) but keep 127.7 people out of the ICU. It makes a stark case. In most of the Winton Centre groupings, the risk of the AstraZeneca vaccine pays off.

Again, though, the US and Europe ceded the power to evaluate these vaccines to the companies that made them. Each one used slightly different protocols and different populations. A multi-arm study of all of them might have ironed out these statistical kinks. The WHO actually announced such a trial in 2020; nothing seems to have come of it.

For one thing, a multi-arm trial would have made it easier to figure which vaccines’ risks and benefits best match to specific subgroups. That would’ve taken the my-risk/my-benefit hesitancy argument at least partially off the table. “It is wrong to compare vaccines based on relative risk reduction when the studies were done differently,” Olliaro says. “They were done with different protocols, different definitions of what a case is, and completely different populations with different risks.” Put all those vaccines together with the same endpoints and well-understood populations, though, and you get answers to which one is better for whom.

The researchers running my made-up trial might’ve also built in an early, robust look at how each vaccine mitigated milder cases of Covid-19 and its transmission. That would’ve cut deep into the hesitancy arguments.

People might think that their risk of getting Covid-19 isn’t high enough to bother with vaccination—and that in fact the risk of vaccine side effects outweighs it. That argument presupposes a lot. It assumes that an asymptomatic or mild case of Covid-19 is no big deal, and it ignores the way the virus that causes Covid-19 moves from person to person.