The first is that a vaccinated person could theoretically still transmit the virus. This isn’t typically an issue after vaccination against respiratory viruses, once your body develops antibodies and other means of immune memory. If you inhale the virus again, these defenses should identify and eradicate it before it multiplies in large numbers. But that doesn’t mean viral particles can’t briefly cling to your nasal cavity and replicate before your body’s alarms go off, creating a brief window in which you could transmit the virus to someone else. This coronavirus warrants special caution because we know that it can be transmitted by people who have no symptoms and low levels of virus in their bodies. That means it is especially adept at lingering in the noses of people without quickly triggering an immune response (which is the source of most symptoms, such as cough, muscle aches, fever).
The vaccines that have been rolled out in the U.S. do seem to be extremely, surprisingly effective at preventing people from falling sick with COVID-19, but the clinical trials did not monitor the mechanisms through which this protection is conferred. People were not tested to see when and how reliably they developed antibodies, nor screened to see whether they ever carried the virus. Additional research is under way to address these questions in coming months. Although I would be surprised to learn that vaccinated people are spreading the virus to any significant degree, it’s reasonable to have everyone continue wearing masks until we know more.
The second variable in the countdown to mask-free life is how quickly entire communities get vaccinated. When the virus is spreading widely and very few people are vaccinated, the chance that a vaccinated person will carry the virus (and possibly even get sick, since no vaccine is 100 percent effective) is simply too high to suggest that anyone forgo masking. But as more and more people get vaccinated, the potency of each vaccine grows. Even if vaccinated people do prove to have the potential to carry and spread the virus in small amounts, for brief periods, that risk can be rendered moot if almost everyone gets vaccinated.
All of this is contingent on the assumption that immunity generated by vaccines is reliable and long-lasting (which it seems to be, so far) and that the virus does not evolve to become resistant to this immune protection in the near term. Eventually, it likely will. But by that point, hopefully, the rates of transmission will be low enough that we can quickly identify new variants and modify vaccines accordingly, to stay ahead of any new surges.
The bottom line is that the less the virus is circulating in the U.S., the more confident we can be transitioning away from masks. Unfortunately, we haven’t collectively actually started wearing them. More than 3,000 people are dying every day in the U.S. alone, and hundreds of thousands more are being infected. This wouldn’t be happening if we were all wearing masks effectively. Before we truly begin to think about the end of masks, we need to think much more seriously about how to use them better.