May 17, 2021 – Organ transplant recipients remain vulnerable to COVID-19, even after they’ve been fully vaccinated against the virus, new research shows.

"It is highly concerning that only a little over half the population developed antibodies to the vaccine because we know in healthy people, it's nearly 100%," lead author Brian Boyarsky, MD, a research follow at Johns Hopkins University School of Medicine in Baltimore said..

"The take-home message from this is that transplant recipients and certain other immunocompromised people should not assume immunity after vaccination."

The study was published online May 5 in JAMA.

Immunocompromised Absent From Vaccine Trials

Organ transplant recipients and others with immune system problems were largely excluded from COVID-19 vaccine trials, making the new study’s results especially important..

"In general, transplant recipients have a slightly blunted response to vaccination, but this was a novel mRNA platform, so we just didn't know how these vaccines would work in these patients," Boyarsky explained.

In a previous study, Boyarsky and his team found that most solid organ transplant recipients did not show significant antibody responses to the first dose of the vaccine.

Q&A With Dr. John Whyte (May 14, 2021)WebMD's Chief Medical Officer, John Whyte, MD, MPH, answers viewers' questions about COVID-19 vaccines and blood thinners, infectiousness, and gatherings.143

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To see how a second dose affected transplant patients, the researchers looked at data on 658 transplant recipients from across the United States who received two doses of the Pfizer or Moderna vaccine between December 2020 and March 2021.

At a median of 21 days following the first dose, antibodies were detectable in 15% of participants. After a median of 29 days following the second dose, only 54% of participants had detectable antibodies.

Despite the fact that people who are immunocompromised tend to have lower responses to vaccines in general, the response among patients overall was unexpected, Boyarsky said..

"What surprised us was the magnitude of the decreased immunogenicity in these patients," he said.

"To us, this means that clearly there's some interplay between the transplant immunosuppression and perhaps the underlying diseases or comorbidities that the patients have that renders these vaccines less immunogenic in our populations."

Potential options for improving antibody responses could be the addition of a booster shot or the changes in treatment for people immune system disorders.

"That's something that would have to be done in a very careful manner because these immunosuppressive drugs obviously are very important for the transplant recipients to...prevent their bodies from rejecting the organs," Boyarsky explained.

He underscored, however, that the findings do not necessarily suggest that transplant patients get no protection from the vaccines, and, considering their higher risk of serious effects from COVID-19, patients should nevertheless be vaccinated.

"Just because we're not detecting robust antibody responses to vaccination doesn't mean that there aren't other cells at play in the immune system, for example T cells or memory B cells, that may contribute to some level of immunity or protection from severe disease. We also recommend family members and social networks of transplant recipients also absolutely get vaccinated to help protect the most vulnerable members of society."