COVID-19 Vaccine Booster Shots May Increase Antibodies in Transplant Recipients

A new study shows that administering a third COVID-19 vaccine dose to solid organ transplant recipients may sufficiently increase their antibodies.

The study, published in Annals of Internal Medicine earlier this month, observed 30 fully vaccinated transplant recipients with no or low levels of antibodies. Researchers found markedly increased antibodies in these patients, especially those who had low positive antibody levels, after they received a third COVID-19 vaccine shot. 

Although the study shows promise in providing better COVID-19 protection, further research is needed to be certain whether higher antibody levels are associated with increased immunity against the virus.

Reduced Antibody Responses in Transplant Recipients

Transplant recipients often take immunosuppressive medications to prevent their immune system from rejecting the transplanted organ. However, suppressing the immune system also inhibits its response to infections and vaccines, which causes a suboptimal antibody response after two doses of COVID-19 vaccines, experts say.

“Many studies now show that solid organ transplant recipients are producing lower levels of anti-spike antibodies after completion of the COVID-19 vaccines,” Inci Yildirim, MD, pediatric infectious diseases specialist at Yale Medicine, tells Verywell. “This is not unexpected given the reduced antibody responses to other vaccines such as seasonal influenza vaccines in this patient population.”

Although the recent study shows that antibody levels can be increased with an additional vaccine dose, higher antibodies don’t automatically indicate an increased immunity. It’s crucial to examine how transplant recipients respond to COVID-19 vaccines because they are more likely to get severely ill from the disease due to their immunocompromised state.

“The concentration or the level of the antibody is only one of the many surrogates we can check to see if the vaccine induced a response,” Yildirim says. “However, whether this level translates into the functionality of the antibody is not known. In addition, we don’t know how long the protection will last and how this correlates with the antibody levels.”

Antibody Tests Cannot Evaluate COVID-19 Immunity

Antibody tests are typically used to detect previous SARS-CoV-2 infection, but experts do not recommend them for evaluating post-vaccination immunity. There is currently no means to check an individual's degree of protection from COVID-19 at any time, including after vaccination.

Most antibody tests do not measure neutralizing antibodies that would thwart the virus, William Moss, MD, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, tells Verywell.

Cell-mediated immunity, an immune response that doesn’t involve antibodies, is also unmeasurable via antibody tests. This highlights the study’s limitations in accounting for the amount or functional activity of neutralizing antibodies as well as the B-cell and T-cell responses of the participants.

“Although it is likely that these higher antibody levels mean increased COVID-19 immunity, we are not absolutely sure,” Moss says. “This [study] provides hope that some of these patients can be protected by additional vaccine doses, although more research is needed.”

Studies are underway to see whether a booster dose can provide average individuals with better immunity against COVID-19, which is critical especially if a strain becomes resistant to the protection afforded by the current COVID-19 vaccines. Booster doses may also counter waning immunity over a certain period.

In February, Pfizer began their study to look into the effects of a Pfizer-BioNTech booster dose on those who are fully vaccinated with the same vaccine. Meanwhile, the National Institutes of Health (NIH) started evaluating the use of booster doses from a different COVID-19 vaccine to examine the safety and immunity provided by mixed boosted regimens.

“We still do not know what level of antibody is protective against SARS-CoV-2 infection in the general population and also in solid organ recipients,” Yildirim says. “We do not know what the additional dose of COVID-19 vaccine will provide with regards to the functionality—the protection against infection—of the antibodies induced by the vaccine.”

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