A small Israeli study of vaccinated health care workers found that a handful who got infected developed headaches, muscle pain, fatigue and other symptoms of long COVID that lasted for weeks.

Transcript

ARI SHAPIRO, HOST:

There's more potentially worrisome news today for vaccinated people. In very rare cases, they may be at risk for long COVID symptoms. NPR health correspondent Rob Stein joins us with the details.

Hi, Rob.

ROB STEIN, BYLINE: Hey there, Ari.

SHAPIRO: So yesterday, the CDC revealed the troubling news that fully vaccinated people might still be able to spread the virus. What's new today?

STEIN: It's a new study from Israel, and it's really the first to suggest that vaccinated people may - and I really need to stress the word may - be at increased risk for long COVID symptoms. Researchers at the Sheba Medical Center in Israel have been following hundreds of doctors and nurses and other health care workers who got vaccinated. And the good news is the researchers confirmed that those so-called breakthrough infections are extremely rare. And when they do happen, most people get either no symptoms or just mild symptoms.

But now comes the disturbing part. In this study, about one in five people who got infected even though they were vaccinated - 19% - experienced symptoms found in long COVID patients that lasted at least six weeks.

Here's Gili Regev-Yochay. She led the study.

GILI REGEV-YOCHAY: They had severe fatigue. They continued to have loss of taste and smell. Some of them did not return to work because they were so tired, you know, muscle pain, headaches that were continued. You know, you can say these are potentially mild symptoms, but disturbing enough that some of the people didn't even return to work. It's very concerning.

STEIN: Now, it's really important to stress that these are very small numbers. Out of about 1,500 vaccinated health care workers in the study, only 39 got infected, and only seven had these symptoms that lasted more than six weeks.

SHAPIRO: So with all those caveats and the small sample size, how worried should vaccinated people be?

STEIN: Yeah. So for now, it's definitely not time to sound any major alarm bells. Clearly, you know, more research is needed to see if this holds up when more people are studied over a longer period of time. It could turn out that this is just a false alarm, or it's even rarer than this, or that these symptoms, you know, do end up going away relatively quickly and don't plague people for months, like long COVID. Nevertheless, it is worrying. I talked about this with Dr. Eric Topol at the Scripps Research in California.

ERIC TOPOL: We had hoped that when you get vaccinated, and even if you did have a breakthrough infection, that you had enough of an immune response that would block this protracted symptom complex now known as long COVID. This study is really the first to give us an indicator that there's some long-haulers among that small group of people who had breakthrough infections.

STEIN: Now, it's also important to note that this study was done when the alpha variant was dominating Israel. And since delta's so much more contagious and tends to produce even more virus inside people's bodies, if anything, the problem could be even worse now.

SHAPIRO: That does sound like an important detail. So what should vaccinated people do about this?

STEIN: You know, the first thing everyone stresses that I talked to about this is that the vaccines are still really powerful at doing the most important thing, which is, you know, keeping people from getting really sick or dying. So the most important thing anyone can still do now is get vaccinated. But it is a reminder that vaccines, you know - they're not perfect. And this virus keeps turning out to be nastier than we've thought. Here's Saad Omer. He's a vaccine expert at Yale.

SAAD OMER: You can imagine your vaccine providing a bit of a force field, but that's not the case anymore. It's still pretty strong armor, but it's penetrable armor.

STEIN: And it could turn out that some vaccinated people do end up with health problems that linger. So this is just one more reason why it's more important than ever that vaccinated people not let down their guard and, you know, follow those new recommendations from the CDC that they put back on their masks when they're in risky situations.

SHAPIRO: That is NPR's Rob Stein.

Thanks a lot, Rob.

STEIN: You bet, Ari. Transcript provided by NPR, Copyright NPR.