Why people who get the COVID-19 vaccine still need to wear masks

Questions surrounding immunization & transmission
Why people who get the COVID-19 vaccine still need to wear masks
Posted at 3:30 PM, Dec 10, 2020
and last updated 2020-12-10 20:46:15-05

SAN DIEGO (KGTV) — Even though Americans could start getting vaccinated in days, experts say people who get the shot will still need to wear masks and practice social distancing until scientists can answer a key question: whether immunized people can continue to spread COVID-19.

The clinical trials by Pfizer and Moderna showed the two vaccines were about 95 percent effective, but what that really means is they were 95 percent effective at preventing COVID-19 symptoms.

The trials did not measure whether vaccinated volunteers got infected without showing symptoms.

That means “it is possible and conceivable” that immunized individuals could still be silent spreaders, said Dr. Christian Ramers of Family Health Centers of San Diego. “You’re not going to get sick, but you still get an asymptomatic case, pass it on to your grandmother and kill her.”

Both the Pfizer and Moderna vaccines are injected into the arm muscle to stimulate production of antibodies. From there, the antibodies can quickly get to the lungs to fend off severe infection. But experts say the antibodies may have less access to the nose and throat, the primary entry points for the virus.

Some studies have suggested that people without symptoms can still have high enough levels of coronavirus in their nose to infect other people.

“The vaccine is doing something to prevent disease. We don't really know yet if it prevents transmission,” said Dr. Ramers. “So we have to fall back on all those fundamental things like distancing, masking and washing hands.”

Still, experts say there are encouraging clues that vaccinated people may be less contagious. A study in October found antibody levels in the blood were similar to levels in saliva.

AstraZeneca had volunteers in its trial test themselves for signs of infection and reported there were fewer asymptomatic cases. However, the company has not yet provided details and its vaccine relies on different technology than Pfizer and Moderna’s mRNA candidates.

Until we know more, doctors say vaccinated people will have to keep wearing masks -- potentially until there we achieve herd immunity.

“There is modeling to suggest that it will be summer until we reach the point where there are enough people vaccinated that this curve of new cases really starts to go down,” Ramers said.

There’s a chance we could get good news before then. Both Pfizer and Moderna say they’ll start testing their volunteers’ blood to reveal if they got infected after vaccination.

Pfizer plans to examine a subset of its volunteers. Moderna said it will analyze blood from everyone in the trial.

Moderna said it will take several weeks to produce results.