Can You Spread the Coronavirus After Vaccination?

“No definitive clinical trial can give you this evidence,” Rasmussen stated. The trials were actually created for speed and security, so the scientists were most worried with trying to find symptomatic COVID-19 or negative responses, not asymptomatic infections. To understand how frequently immunized individuals were asymptomatically bring the infection, scientists would have needed to evaluate each of the 10s of countless individuals in their medical trials as regularly as possible.

Some continuous trials have actually required to swabbing the noses of immunized individuals periodically, and this might include insight into how typical it is for individuals to bring the infection after vaccination. Early proof from Johnson & Johnson’s medical trial, for instance, recommends a considerable decrease in transmission after vaccination, though this stays to be validated. Still, periodic screening is bound to miss out on cases of infection, and discovering some infection in some noses doesn’t inform us how transmittable the owners of those noses may be—or whether they’re transmittable at all.

The only method to address this concern for specific would be to run a “challenge” trial in which immunized and unvaccinated individuals were intentionally exposed to the infection under comparable conditions, and after that evaluated to see what portion of them got contaminated. That’s simply step one. Then the vaccinated-but-infected individuals would require to hang out with a lot of unvaccinated individuals to see if they got contaminated, and at what rate. This is not going to happen. Challenge trials are ethical minefields in normal times; at this point, any study that involves withholding a vaccine from a control group would be difficult to justify.

More trial data are expected over the next few months, and these may help narrow our uncertainty. It would certainly be useful to get a better sense of whether the risk of catching COVID-19 from your grandmother, for example, drops by something like 90 percent once she’s vaccinated, or whether it’s closer to 10 percent—but that number isn’t going to be exact, and it won’t be static, either. Even if we could somehow run the sort of challenge trial described above, whatever value it produced could change as new variants of the virus take hold, and it might well vary across regions with different patterns of prior infection, behavioral norms, local weather, and other variables we don’t even know to look for.


All of this is academic. Whatever trial data might arrive in the coming months won’t change the practical advice: As long as a lot of virus is still circulating in a community and many individuals remain unvaccinated, the mere fact that some have protection will not mean that it’s  responsible for them to forgo precautions and do whatever they like.

A different kind of data, though, will offer that reassurance and certainty. This is what we’re really waiting on. “We will absolutely get to a point when we can say that vaccinated people don’t need to wear masks,” Madad said, but that will be driven largely by changes in the number of cases, and in the vaccination rate. The sooner we can drive the former down and the latter up, the sooner normalcy returns. As populations draw closer to herd immunity, the chance of a vaccinated person both carrying the virus and coming into close contact with a nonimmune person will become so low that the guidelines will change. But as long as the virus remains omnipresent, the risk of getting contaminated (and transmitting) the virus after being immunized stays expensive to countenance.

Jobber Wiki author Frank Long contributed to this report.