Dhruv Khullar writes:

Beyond the dread that I feel for my patients, my work as a physician on the coronavirus wards has instilled in me two related fears. The first fear, which surges each time I learn about another of the nearly two thousand health-care workers who have died of Covid-19, is that I will get infected and fall seriously ill. A second, deeper and more persistent, fear is that I will pass the virus to my family. It’s because of this concern that I still isolate from them while caring for coronavirus patients.

Like other doctors in my hospital, I’ll be getting vaccinated sometime in the next week or two. I’ve spent some time thinking about how this will change my behavior and state of mind. Getting the shot will put the first fear to rest: we know for sure that the vaccines developed by Pfizer and Moderna prevent severe illness in almost all people who are inoculated. But it won’t eliminate the second fear, because we’re not yet certain that the vaccines can prevent people from becoming infected or infecting others. It’s a distinction with a difference.

Consider the H.P.V. vaccine. It’s extraordinarily effective at reducing genital warts and cervical cancer in women who get inoculated; it has also, happily, driven down the incidence of H.P.V. among unvaccinated men, because, in addition to preventing illness, it stops vaccinated people from contracting, then transmitting the virus to others. Many vaccines, including those for measles and chicken pox, work this way. But others, such as the new shot against meningitis, don’t. That shot reduces the chances that vaccinated people will get sick, but it doesn’t do much to stop the spread of Neisseria meningitidis, the bacteria that causes meningitis, from one person to the next.

At the moment, we don’t know how the new coronavirus vaccines will affect transmission. While conducting their clinical trials, Pfizer and Moderna tracked how many vaccinated people got sick with covid-19; they didn’t study whether the virus infected them. It’s possible that inoculated people in the trial caught the coronavirus, but that the vaccine prevented them from developing symptoms. If that happened, it would hardly lessen the astonishing nature of these vaccines, which have been developed in record time and prevent illness with an efficacy that was unthinkable just a few months ago. But it would mean that vaccinated individuals, without getting sick themselves, could give the virus to unvaccinated people—that is, to the majority of Americans, for months to come. [Continue reading…]