by Vinay Prasad, MD, MPH  

Over the last week, the topic of COVID-19 booster shots -- a third dose of mRNA vaccine for healthy Americans -- has been thrust into the spotlight. The surgeon general, CDC director, Anthony Fauci, MD, and President Biden have announced that they wish for boosters to be available by late September for healthy adults who are 8 months out from their original two-dose series. While this will be contingent on an FDA evaluation to determine the "safety and effectiveness of the third dose," a clear path forward has already been set. And just like everything else throughout the course of the pandemic, the choice has been made with a dearth of data and an abundance of political pressure. (MedPage Today)

Diminishing vaccine effectiveness supposedly makes the case for boosters. But there are two big questions here: First, what is current vaccine effectiveness? And second, what justifies boosters? Let's consider these in turn.

What Is Vaccine Effectiveness Now?

We have to be honest, many vaccine effectiveness studies are poorly done. All studies compare the rate of getting a breakthrough infection among vaccinated people against the rate of infection in unvaccinated people. But there are some issues with this approach. First, as time goes on, more unvaccinated people have had and recovered from COVID-19 (and these individuals may be less likely to go on to get a shot). This means that their risk of getting COVID-19 a second time is far less than the typical unvaccinated person who has never been sick. Even if vaccines "work" as well as before, this factor alone will result in the appearance of diminishing vaccine effectiveness. 

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