Lifestyle Health Johnson & Johnson Vaccine Recipients May Be Better Off with a Booster of Pfizer or Moderna: FDA An FDA advisory panel will meet Friday to determine what type of booster shot is best for people who received the Johnson & Johnson vaccine By Julie Mazziotta Julie Mazziotta Twitter Associate Editor, PEOPLE Health People Editorial Guidelines Published on October 14, 2021 12:20 PM Share Tweet Pin Email A medical professional giving a vaccine shot. Photo: Getty People who received Johnson & Johnson's single-dose COVID-19 vaccine may be better off getting a booster shot of Pfizer or Moderna's vaccine rather than a second dose, according to data reviewed by the Food and Drug Administration. The FDA went through two studies — one from Johnson & Johnson, which has been testing the effectiveness of a second dose of their vaccine and another that looked at following the Johnson & Johnson vaccine with a booster shot of Pfizer or Moderna, which are mRNA vaccines that use a different delivery system to create antibodies that protect against COVID-19. While a second dose of Johnson & Johnson did improve the immune response among people who received the vaccine, the other study, which has not yet been published, found that a booster shot of Moderna led to the biggest increase in antibodies, a 76-fold improvement. The Pfizer vaccine added a 35-fold boost in antibodies, and a second Johnson & Johnson dose just 4-fold. The researchers, from the National Institutes of Health, said though that there are limitations to their study — it was small and the follow-up period was short, plus they did not look at whether any of the participants got infected during the study. An expert advisory panel will meet on Friday to discuss the data and determine if they will recommend a booster shot of any kind for Johnson & Johnson recipients, and will also go over a request from Moderna to approve third doses of their vaccine. The FDA and Centers for Disease Control have already approved a booster shot for Pfizer recipients over 65 years old, those who are immunocompromised and people with high-risk jobs. RELATED VIDEO: FDA Grants Full Approval to Pfizer's COVID Vaccine Current data shows that the single-dose Johnson & Johnson vaccine is 56% effective in preventing moderate or severe COVID-19 illness, compared to Pfizer or Moderna's vaccines, which are more than 90% effective. A second dose of Johnson & Johnson brings the vaccine up to 75% effectiveness against any illness and 100% effective against severe disease. The majority of Americans, around 103,600,000, have received Pfizer's vaccine, while more than 69,250,000 got Moderna. Just under 15,000,000 Americans received Johnson & Johnson, though the vaccine's rollout was hampered by temporary pauses in inoculations as the CDC verified that it was safe for use, and a manufacturing mix-up that led the company to throw out 15 million doses. As of Oct. 14, just over half of Americans, 56.6%, are fully vaccinated against COVID-19 and 65.6% have received at least one dose. Of the Americans eligible to get vaccinated, those aged 12 and up, 66.2% are fully vaccinated and 76.7% have received at least one dose. As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from the CDC, WHO and local public health departments. PEOPLE has partnered with GoFundMe to raise money for the COVID-19 Relief Fund, a GoFundMe.org fundraiser to support everything from frontline responders to families in need, as well as organizations helping communities. For more information or to donate, click here.