While early data regarding a fourth dose of Pfizer BioNTech and Moderna COVID-19 vaccines indicate they increase antibodies, the boost is likely not enough to protect from omicron infection.
Dr. Gili Regev-Yochay, director of the Infection Prevention and Control Unit at Sheba Medical Center in Ramat Gan, Israel, said the level of antibodies needed to prevent omicron infection “is probably too high for the vaccine, even if it's a good vaccine,” according to CNN.
As of this week, more than 99 percent of COVID-19 cases in the U.S. are caused by the omicron variant of the virus, per Centers for Disease Control and Prevention data. This variant was first identified in November and caused case spikes around the world.
The following month, Sheba Medical Center started trialing a fourth dose of the vaccines for healthy people ahead of a rollout of the shots for at-risk individuals – the first study of its kind. This study included 154 health care workers who were given a fourth dose of the Pfizer vaccine, 120 who were given a fourth dose of the Moderna vaccine and a control group who did not receive fourth doses.
Early data indicates individuals produced more antibodies after the fourth shot than after the third, with fewer infections observed among those who got the vaccine. Pfizer and Moderna shots seemed to be equally effective.
“These are very preliminary results,” Regev-Yochay said Monday. “This is before any publication, but we’re giving it out since we understand the urgency of the public to get any information possible about the fourth dose.”
In the U.S. third booster doses are currently available to those who received Pfizer and Moderna two-dose vaccines, as well as boosters for those who received the single-shot Johnson & Johnson vaccine. As of January, the CDC recommends that only immunocompromised people receive fourth doses, since they recommend a three-dose initial vaccine series to those individuals.
Booster doses are recommended two to five months after the initial series, depending on the first shots received.
“I think that the decision to allow the fourth vaccine to vulnerable populations is probably correct,” Regev-Yuchay said. “It may give a little bit of benefit, but probably not enough to support the decision to give it to all of the population, I would say.”
Both Pfizer and Moderna are working on vaccines that would specifically target the omicron variant, which appears to be more contagious but less deadly than other COVID-19 variants. Moderna expects to release data in March and Pfizer expects its vaccine to be available that same month.