A third dose of the coronavirus vaccine could help increase antibody levels in some organ transplant recipients who haven’t had strong responses to standard immunization schedules, a new study suggests.

Among the patients in the study who did not have measurable antibodies after receiving two doses of the vaccine, a third saw an increase in antibodies after a third dose – and among those with low levels of the vaccine. antibodies after two doses, all saw an increase after a third dose. The results were published Monday in the journal Annals of Internal Medicine.

Organ transplant recipients might not have an adequate response to coronavirus vaccines because they are taking drugs to suppress their immune system. This helps reduce the risk of the body rejecting new organs, but can also limit responses to vaccines.

When it comes to coronavirus vaccines, “we don’t really have a good idea of ​​what level you need for protective immunity,” Dr. Dorry Segev, study author and founder of the Epidemiology Research Group in Organ Transplant to Johns Hopkins University, told CNN. “We don’t know if you need the same outsized level of antibodies as people with normal immune systems.”

When pharmaceutical companies tested vaccines against the coronavirus in clinical trials last year, they specifically excluded people who were taking immunosuppressive drugs because of the potential risks.

But for transplant patients, after a full series of two-dose vaccines, “the overwhelming majority have no antibodies or weak antibodies,” Segev said.

Increase antibody levels

The researchers, at Johns Hopkins University School of Medicine in Baltimore, looked at antibody responses and vaccine reactions in 30 organ transplant patients who received a third dose of the coronavirus vaccine between March and May of this year. Fifteen patients received a dose of the Johnson & Johnson vaccine, nine received the Moderna vaccine and six received the Pfizer vaccine approximately 67 days after completing the second dose of their original vaccination.

The researchers tested the patients for antibodies before they received their third dose of the vaccine. They found that 24 patients had no detectable antibody levels and six had low levels.

The patients were retested for antibodies about two weeks after receiving a third dose of the vaccine. The researchers found that the six patients who previously had low antibody levels all had high antibody levels after their third dose. Of the patients with no detectable level of antibodies, six had high levels, two had low levels, and 16 remained undetectable after a third dose.

About a week later, 23 of the patients who completed a questionnaire about their reactions to the vaccine after receiving a third dose reported typical reactions such as pain at the injection site, fatigue, headache, or muscle aches.

In a heart transplant recipient, there was evidence of mild organ rejection a week after her third dose, the researchers found. But her heart function remained normal and the rejection resolved without the need to step up her immunosuppressive regimen.

The researchers also noted that she had not experienced an increase in antibodies and that “it is not certain” that the only case of mild rejection was related to the vaccination.

The new study comes about a month after Segev and his colleague published research in the medical journal JAMA that found that among 658 transplant recipients who received two doses of the Pfizer or Moderna vaccines, nearly half had no response. into antibody after two doses. They found that 15% had measurable antibody responses after the first and second dose and 39% had no antibody response after the first dose but a subsequent antibody response after the second.

Antibodies are not everything

Antibodies are only part of the body’s immune response, so experts say future studies on boosters should also measure the activities of other parts of the immune system besides antibodies, such as T cells and T cells. B cells.

In April, French health authorities recommended a third dose of the vaccine for immunocompromised people. In the United States, emergency use authorizations “limit people to one standard set of vaccines,” Segev said. “And what happens is the transplant patients are given the series of vaccines, they get their antibodies checked, they realize they’re low, they talk to their doctors, and then they’re going to get a third dose for it. try to reinforce that.

Various medical societies, such as the American College of Rheumatology, the American Society of Transplantation, and the International Organization for the Study of Inflammatory Bowel Disease, essentially say that antibody tests will not fully answer questions. of patients on the effectiveness of their vaccinations.

The United States Food and Drug Administration and the United States Centers for Disease Control and Prevention also do not recommend testing for antibodies.

The National Institutes of Health is working to determine which approaches might work best if the vaccine fails in people who are immunocompromised. This summer, researchers hope to start recruiting around 200 vaccinated kidney transplant patients to participate in a booster study, Dr Daniel Rotrosen, director of the Division of Allergies, Immunology, told CNN earlier this month. and transplantation to NIAID.

If tests show the Covid-19 vaccine has not worked well, that study participant will be offered an extra dose of the vaccine to see if that helps, Rotrosen added. Segev and his colleagues will be involved in this work.

“We hope to launch a clinical trial in one to two months, an interventional trial, where we can administer a third dose of vaccine to people, and study in a very systematic way the impact of this third dose on the response of the immune system”, Segev said. He added that the new study provides strong evidence that boosters would be helpful in this patient population.