With Johnson & Johnson’s one-shot vaccine close to distribution in the US, the end of the pandemic seems a big step closer. But not everything will return to normal right awayPublic health authorities want people to keep wearing masks and social distancing, even after they receive a vaccine. This might seem counterintuitive – after all, if someone gets a vaccine, aren’t they protected from the coronavirus? The answer is complicated: the vast majority of people who are vaccinated will be protected from Covid-19, the disease caused by the SARS-CoV-2 virus. However, vaccinated people may still be able to transmit the virus, even though they do not display any symptoms. “We know now the vaccines can protect, but what we haven’t had enough time to really understand is – does it protect from spreading?” said Avery August, professor of immunology at Cornell University. That is because the the SARS-CoV-2 virus may still colonize the respiratory tract, even as systemic immune cells protect the overall body from the disease it causes – Covid-19. Here is how this works: default When can I stop wearing a mask? Hold on to your mask(s) for the foreseeable future. Right now, there are several unknowns, which make mask-wearing and social distancing important to protect the wider community. First, scientists do not know how Covid-19 vaccines may protect against asymptomatic transmission of SARS-CoV-2 (as explained above). There are promising signs – but research remains incomplete. Researchers also do not know how long Covid-19 vaccines may protect people from the virus. Scientists will also be closely watching how evolutionary changes in the virus, or variants, impact the effectiveness of vaccines. Researchers have already found efficacy of the Johnson & Johnson vaccine was reduced in South Africa, where the B1351 variant is present. However, the most important factor may be the extent to which eligible adults accept the vaccine. Children are able to spread the disease, but not eligible for the vaccine; some people may be too immune-compromised to take it; and others may face bureaucratic barriers to vaccination. What’s the point of getting the vaccine if I still have to wear a mask? Think of mask-wearing and social distancing as a continuum of risk-mitigation strategies, which are in place while scientists conduct research, more and more people get vaccinated, and the prevalence of Covid-19 goes down. For example, as vaccines continue to roll out, small gatherings of vaccinated people will become more common. Those same people then need to be conscientious about social distancing and mask-wearing in public, as they could potentially transmit the disease in the wider community. The hope is that as more and more of the public is vaccinated, fewer people will have severe cases of Covid-19, and the pressure on the health system will decline with the prevalence of the disease. “Hopefully we can get a majority of the population vaccinated,” said Dr Bruce Y Lee, a professor of health policy at the City University of New York’s School of Public Health. “That’s when we can start talking about moving toward normal.” When will we have these answers? Studies on the extent to which vaccines protect against transmission are continuing, and promising, but incomplete. It is unlikely the vaccines will provide complete, or “sterilizing”, protection. Only a handful of vaccines are able to make that claim, including for example the smallpox vaccine. However, if a vaccine significantly reduced transmission, it would be very good news for the world’s ability to contain the virus. Under normal circumstances, these kinds of questions might have been answered in years-long vaccine clinical trials. In this emergency situation, stopping the disease was a more important goal, and available vaccines do that very effectively. “We would probably know as more and more people get vaccinated, somewhere near the middle of September,” said August. Importantly though, vaccines do not necessarily need to provide complete protection to help fight the pandemic. “If everyone is vaccinated then there is less virus around,” said August.