As the nation grapples with a wave of Covid-19 infections driven by the highly infectious delta variant, the FDA is now permitting vaccination booster shots—but only for organ transplant patients and others whose medical condition leaves them with weakened immune systems. The FDA has expanded emergency authorization of the messenger RNA vaccines to include this narrow group of patients.
The regulatory action, announced late Thursday, only covers booster shots for the mRNA vaccines from Moderna and partners Pfizer and BioNTech. The status of the third FDA authorized Covid vaccine, from Johnson & Johnson, remains unchanged. The update comes ahead of a scheduled Friday meeting of the Centers for Disease Control and Prevention’s Advisory Committee on Immunization Practices, which will discuss clinical recommendations about vaccination of immunocompromised people.
Janet Woodcock, the FDA’s acting commissioner, said in the announcement that the agency updated the emergency authorizations because immunocompromised people have a harder time fighting off infection, putting them at particularly high risk of developing severe disease. These patients could benefit from the extra protection given by a third shot. She added that those who are fully vaccinated by the authorized Covid vaccines are adequately protected and do not need a booster. That might change.
“The FDA is actively engaged in a science-based, rigorous process with our federal partners to consider whether an additional dose may be needed in the future,” Woodcock said.
The two authorized mRNA vaccines are given in two-shot regimens. The Pfizer shots are given three weeks apart; Moderna’s shots are given four weeks apart. According to the updated authorizations, boosters for both vaccines should be given at least 28 days after patients have received second shot of the regular two-shot vaccination regimen.
In the updated authorization information, the FDA said it reviewed safety and efficacy data from two manuscripts on solid organ transplant recipients. The first was a study conducted in 101 patients who had previously undergone transplants of organs such as the heart, kidney, liver, lung, and pancreas. A third dose of the Pfizer/BioNTech vaccine was given to 99 of these patients about two months after they had received the second shot of the two-dose regiment.
In the 26 of 59 (44%) patients who had tested negative for the virus, study results showed that levels of total SARS-CoV-2 binding antibodies developed four weeks after a third dose of the vaccine. In the entire group, 67 of the 99 patients (68%) who received a third shot were later considered to have antibody levels “indicative of a significant response.”
The results showed the side effect profile of the third shot was similar to what has been observed after the second dose. No serious adverse events were reported.
For the Moderna vaccine, the FDA reviewed results of a study in which 60 patients were given a third shot about two months following the second dose. That study compared these patients to 60 people given a saline placebo. The main goal was to measure levels of an antibody for the receptor binding domain of the novel coronavirus.
The results showed that in 33 of the 60 patients (55%) given a third Moderna dose, the level of total SARS-CoV-2 binding antibodies indicative of a significant response” occurred four weeks later. In those who were given a placebo as a third shot, 10 of the 57 study participants (17.5%) showed such a response. Like the Pfizer/BioNTech third shot, the Moderna booster’s side effect profile was similar to that of the second dose of the vaccine and no serious adverse events were reported.
Authorization of the Pfizer-BioNTech Covid vaccine covers those age 12 and older. The Moderna vaccine is authorized for people 18 and older; in June the Cambridge, Massachusetts-based biotech filed a request to expand the authorization to include adolescents.
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