We are in a race against time, and the virus appears to be gaining an unfortunate ability to sprint just as we get closer to the finish line. Although the initial rollout of the vaccines has been slow, it is expected to increase rapidly. The U.S. may have 50 million to 100 million people vaccinated as early as March. That is a huge difference, one that could save many lives, especially since we also have perhaps that many people with some degree of postinfection immunity.
Here's how to think about it: Vaccinated people are a lot less likely to get sick in the first place. One hundred million vaccinated people will mean 100 million people with much less (or hardly any) risk for any symptomatic COVID-19, especially severe disease. That's an enormous gain.
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But that's not all. Vaccines benefit not just the vaccinated, but potentially everyone else, too. Fewer people symptomatically sick with a contagious virus means fewer sick people infecting even more people. Every indication we have suggests that vaccinated people will also transmit less—how much less is still being studied, but the difference may well be substantive. The mRNA vaccines (both already approved in the United States) cut down symptomatic disease by about 95 percent. We already know that people who never develop symptomatic disease are
a lot less likely to transmit COVID-19. (Note the difference between people who are truly asymptomatic and people who are just about to get sick—
presymptomatic—but are highly infectious.) In a preliminary study, the Moderna vaccine was found to even prevent
two-thirds of asymptomatic infections. Vaccinated people are thus not only much, much less likely to get any disease; they appear much less likely to get even a silent, asymptomatic infection. Although we need more data to be sure, all of this strongly suggests that vaccinated people will also transmit less. The fewer people there are to efficiently transmit a pathogen, the harder it is for that pathogen to spread.