That suggests vaccine-induced immunity is likely highest shortly after people get their recommended two doses of the vaccine and starts to drop afterward. The Moderna vaccine received emergency use authorization (EUA) from the U.S. Food and Drug Administration in Dec. 2020; the FDA is currently reviewing the company’s request for full approval of the shot. The latest data are part of an ongoing Phase 3 study that includes more than 14,000 people who were randomly assigned to receive either two doses of the Moderna vaccine or two doses of placebo from July to October 2020, and more than 11,000 people who were initially given to receive placebo doses from December 2020 to March 2021 and, after the EUA was granted.
Chose to receive two doses of the vaccine. In that latter group, which completed its two-dose regimen about eight months ago, 88 people tested positive for COVID-19, compared to 162 who had breakthrough cases in the earlier vaccinated group. That means the more recently vaccinated people had a 36% lower incidence of breakthrough infections than those immunized a year ago. (Overall, only 19 of the 250 breakthrough cases were severe.)The results, Moderna says, suggest protection wanes over time, which is why the company submitted data to the FDA to authorize a booster dose to provide better protection against COVID-19.
To make its case for an additional dose, Moderna’s scientists published results from another study on Sept. 15 in the journal Nature Medicine, comparing the efficacy of four different types of booster approaches. In the small study of 79 people, some received a third dose of the same two-dose vaccine they already received, some got a dose of a vaccine developed specifically against the Beta variant, some received a lower dose of this Beta variant vaccine, and a final group received a combination of the original and Beta variant shots.
The data confirmed that about six months after people are fully vaccinated with two doses, levels of antibodies that can neutralize the original version of SARS-CoV-2 dropped by about six- to seven-fold. But boosting with an additional amount of any of the four vaccines, the researchers tested increased levels of antibodies about a month later. The combination dose was the most effective, increasing antibody levels by 46-fold, compared to a 16.7-fold increase with the third dose of the existing vaccine, an 11.3-fold increase with the Beta-specific booster, and a 9.2-fold increase with the lower dose Beta-specific booster.