A third dose of a Covid-19 vaccine may boost protection for some people with weakened immune systems, according to a study published Monday in the Annals of Internal Medicine.
The study, from researchers at Johns Hopkins University, included 30 organ transplant recipients, all of whom had been fully vaccinated with two doses of an mRNA vaccine, either Pfizer-BioNTech or Moderna. Because organ transplant recipients must take immune-suppressing medications to ensure that their body does not reject the transplant, there’s concern that they may not develop robust responses to the vaccines, leaving them vulnerable to Covid-19.
Indeed, despite being fully vaccinated, the vast majority of patients in the study — 24 patients — had no antibodies against the coronavirus, and six patients had only low levels.
So, the researchers gave them a third dose of the vaccine, either Pfizer, Moderna or Johnson & Johnson. About two weeks later, their antibody levels were measured again. In patients who had no antibodies to begin with, eight had an increase following their third dose of the vaccine. And in the six patients who started off with low levels, all had an increase in antibodies against the coronavirus.
Though the study was small, the findings could be important for millions of Americans who are immune-compromised and still vulnerable to Covid-19, even after being vaccinated. According to the United Network for Organ Sharing, more than 17,000 transplants were performed in the first five months of 2021 alone.
“To me the main message here for transplant patients and immunosuppressed patients is a message of hope,” said Dr. Dorry Segev, an author of the study and associate vice chair for research and professor of surgery at Johns Hopkins University.
That message has been received by organ transplant recipients such as Tamsin Skeels, 50, of Charlotte, North Carolina.
Skeels, who was not a part of the new study, underwent a liver transplant in September 2019, just a few months before the pandemic hit.
A few months ago, she got the Covid-19 vaccine under the guidance of her physicians.
But they cautioned her to remain vigilant about avoiding infection. "Don't change your behavior from quarantine," her transplant team advised, Skeels recalled. "Stay at home as much as possible. When you do go out, stay protected. Stay masked and stay distant, even after vaccination."
Even if the vaccines do not offer maximum protection for those with compromised immune systems, they can help indirectly when others get the shots.
"The more people that get vaccinated, the safer people on immunosuppressants will be," Skeels said.
Segev and his team had found in earlier research that only 17 percent of transplant patients mounted an immune response after one dose of a Covid-19 vaccine. After a second dose, that number rose to 54 percent, but that left 46 percent potentially unprotected.
“I’m pleasantly surprised” that some patients in the new study who hadn’t responded to two doses were able to mount a response after a third dose, Segev said.

In recent weeks, a series of covid-19 epidemics related to summer camps have broken out in Texas, Illinois, Florida, Missouri and Kansas. Some people worry that this may be a preview of the coming school year.

In some cases, outbreaks have spread from camps to wider communities.