People who undergo solid organ transplants are at high risk of developing severe COVID-19 infections due to their need to take immunosuppressive medications. These medications, aimed at preventing the body from rejecting a transplanted organ, have the unintended consequence of making immune systems more open to the virus that causes COVID-19.

A new multicenter study—published online in The Journal of Infectious Diseases—has identified a strategy to lessen that risk. It shows that transplant recipients who receive three doses of a COVID-19 mRNA vaccine have greater protection than that provided with two doses. (The Pfizer-BioNTech and Moderna vaccines are mRNA.) The study, by researchers at Washington University School of Medicine, the Centers for Disease Control and Prevention (CDC), and Vanderbilt University Medical Center, examined 10,425 patients hospitalized across 21 hospitals in the U.S. Of those, 440 had solid organ transplants, 1,684 had immunocompromising conditions, and 8,301 had healthy immune systems.

The findings showed that a regimen of two doses of the mRNA vaccine was 29% effective at preventing COVID-19 hospitalizations among transplant patients, while a three-dose regimen was 77% effective. (Solid organ transplants are defined as transplants of the kidney, liver, intestines, heart, lung or pancreas.)

Currently, three doses are widely adopted for people who have had a solid organ transplant. With increasing evidence of the benefits of additional vaccine doses, the CDC now recommends a fourth dose of the mRNA vaccine for people with moderate to severe immunocompromising conditions, including patients who have undergone solid organ transplants.

“Our research confirms that two doses of a SARS-CoV-2 mRNA vaccine do not provide as much protection against hospitalization in solid organ transplant recipients as compared to those with healthy immune systems,” says Jennie Kwon, DO, MSCI, one of the study’s first co-authors and a Washington University infectious diseases specialist. “But the good news is that additional vaccine doses appear to significantly increase effectiveness for solid organ transplant recipients.” Kwon also is a health-care epidemiologist at Barnes-Jewish Hospital, where she treats patients. “The study’s results indicate that solid organ transplant recipients benefit from three doses of mRNA COVID-19 vaccines and support the CDC’s recommendations for this vulnerable population,” she says.

Wesley Self, MD, one of the study’s senior co-authors and an emergency medicine specialist at Vanderbilt, notes: “We believe these results demonstrate that solid organ transplant recipients remain at risk for COVID-19 despite vaccination and support the need for continued efforts to mitigate the risk of COVID in this population.” “Throughout the COVID-19 pandemic, there has been a concern that immunocompromised people, such as those with a solid organ transplant, may not benefit from vaccination as much as immunocompetent people,” Self says. “However, our research illustrates that booster vaccine doses are particularly important for immunosuppressed people.”

The study also points to other measures to reduce the risk of COVID-19 among solid organ transplant recipients, including vaccination of close contacts, individual immune system monitoring and infection prevention strategies, including wearing a mask in public spaces and social distancing.

Originally published by Washington University School of Medicine atmedicine.wustl.edu/news.