Public health officials hope to vaccinate as many people as possible to turn the tide of the coronavirus pandemic once a vaccine becomes available — even those who have already recovered from Covid-19.
And while it isn't yet known how the immune systems of Covid-19 survivors respond to a vaccine — particularly among coronavirus "long-haulers," whose symptoms linger weeks and months after their diagnoses — there is likely to be little risk in getting the shot.
"The general recommendation is to get the vaccine, even if you were previously infected," said Dr. David Thomas, a professor of medicine and director of the infectious diseases division at the Johns Hopkins University School of Medicine. "There are some nuanced questions that we don't have the answer to yet, but from what we know now, it's the right call to get the vaccine."
Covid-19 reinfections are thought to be rare, but if natural antibody levels wane over time, it may be possible for a person to become infected more than once. Doctors and infectious disease experts agree that most people should get vaccinated, even if they may have natural protective immunity. In most survivors, a vaccine might even enhance immunity from the initial infections.
It's a precaution with some precedent. Healthy adults over age 50 are still advised to get the shingles vaccine even if they have had chickenpox or shingles before.
"I did it because I wanted the extra immunity to protect me against a shingles relapse later in life," Thomas said of his recent decision to get the shingles vaccine. "Even though I had previously been infected and had a certain amount of immunity, I chose to get a vaccine nonetheless to double down on that and make me even safer."
The Food and Drug Administration is reviewing data on two vaccine candidates, made by Pfizer and Moderna, and an independent advisory committee for the Centers for Disease Control and Prevention voted Tuesday to approve recommendations for who should be first in line to get the shots. The recommendations will go to the CDC's director for official signoff. The planned rollout has enormous implications for how the country rebounds from the pandemic, but it also raises questions about how the nearly 14 million in the U.S. who have already had confirmed cases of Covid-19 will be affected.
The vaccine trials set up by Pfizer and Moderna included participants from racially and ethnically diverse backgrounds, but they didn't focus on people who were previously sick with Covid-19.
Those types of detailed considerations are part of the vaccine approval process, and Thomas said Pfizer and Moderna would be expected to provide data about a number of outstanding questions even after the FDA initially grants emergency use authorization.
"Typically after something is approved, the FDA will say we're giving you approval, but you have to do all these things in a certain time frame and answer all these questions by a certain date or you lose approval," Thomas said. "Companies are then required to do all these things, but in the meantime, you don't hold everything up."
Some of the stipulations are likely to include specific questions about administering vaccines to people who have had Covid-19, as well as all the accompanying safety data.
So far, there is no evidence that a vaccine would be unsafe for Covid-19 survivors, but more research is needed, said Dr. Sarah Fortune, chair of immunology and infectious diseases at the Harvard T.H. Chan School of Public Health.
"There haven't been any serious adverse events that make me think this would be a major issue, but I think that analysis has to be done," she said. "The first question is about safety, but then the second question is: Is there any added benefit?"
Although the Pfizer and Moderna vaccine trials didn't recruit volunteers who were symptomatic or were known to have been previously infected, it's believed that up to 10 percent of participants in the trials had had the virus, said Dr. Moncef Slaoui, the chief science adviser for Operation Warp Speed, the Trump administration's $18 billion initiative to support the development of coronavirus vaccines. Those people either were asymptomatic or had such mild symptoms that they went undetected, he said.
"What we know is the vaccines are safe in these populations," Slaoui said Wednesday at a news briefing about Operation Warp Speed. He added that more data are needed about how the vaccine works in people who had symptoms and were sick with Covid-19.
Another big unknown is how Covid-19 "long-haulers" may respond, said Michael Betts, an immunologist and professor of microbiology at the University of Pennsylvania's Perelman School of Medicine.
It's not known how many people suffer from long-term symptoms from Covid-19, but a CDC study published in July found that 35 percent of adults who were symptomatic but were never sick enough to require hospitalization hadn't returned to their usual health up to three weeks after their diagnoses.
Part of the challenge of assessing how those patients could be affected by a vaccine is that much is still unknown about why their symptoms persist.
"We really do not understand why these individuals are suffering like this, so my concern comes from the fact that we don't know the reason for these long-haul situations," Betts said.
Thomas said that without a clear grasp of why symptoms linger in certain patients, it's difficult to know whether the immune response from a vaccine would be beneficial or detrimental.
"People who have chronic inflammatory conditions from Covid may fall into a category where you might not want all of a sudden to boost up the immune system," Thomas said. "But it's possible that it might also make them better, too. That's how little we understand this."
Betts said long-haulers may need to be evaluated individually so doctors can evaluate the potential risks and benefits. Those patients will also need to be closely monitored and evaluated over time, he said.
"This might be a special group with case-by-case judgments," Betts said. "We don't really understand the long-haul situation, so trying to predict how a vaccine will perform here is difficult."