The coronavirus vaccines most widely used in the United States remained highly effective at preventing the worst outcomes from infections even in the face of the highly transmissible omicron variant in January, a report released Friday by federal disease trackers shows.
While protection against mild illness waned over time, the mRNA vaccines from Moderna and Pfizer-BioNTech provided a robust shield against death and needing mechanical ventilation, the study from the Centers for Disease Control and Prevention found.
The study bolsters confidence in the vaccines to prevent the most serious outcomes for covid-19 patients, even after the omicron variant fueled an increase in cases, hospitalizations and deaths this winter, said William Moss, executive director of the International Vaccine Access Center at the Johns Hopkins Bloomberg School of Public Health, who did not participate in the study.
Although some fully vaccinated and boosted people came down with mild infections during the omicron surge, the study showed that the vaccines—and especially the booster shot—protected most people from the virus’s worst effects.
“Three doses was better than two—this report highlights the value of the third booster dose,” Moss said.
As omicron became the dominant variant, the vaccine was 79% effective in preventing ventilation or death for people who received the initial series of two doses. The benefit was even greater for people who received a booster shot: During that same time period, the vaccine was 94 percent effective for those people.
“Anybody who is skeptical really needs to look at that number and think, ‘OK, maybe I’m going to get a cold and feel sick, but 94% of the time, I’m not going to get put on a ventilator or die,'” said Jeanne Marrazzo, director of the Division of Infectious Diseases at the University of Alabama at Birmingham.
The study comes as Pfizer and Moderna this week asked the Food and Drug Administration to consider authorizing a second booster shot following data published in Israel that showed vaccine effectiveness decreased as omicron surged. Pfizer requested the FDA allow adults 65 and older to get a second booster; Moderna asked regulators to authorize an additional booster for all eligible adults to allow flexibility for the CDC and health care providers to determine which patients make good candidates for another dose.
If the FDA authorizes an additional booster shot, CDC advisers would weigh in on who should get the extra dose, and the CDC director would have the final say over those recommendations.
The CDC study published Friday looked at cases reported at 21 hospitals across 18 states between March 11, 2021, and Jan. 24, which gives insight into vaccine effectiveness against the alpha, delta and omicron variants. The study also focused specifically on how the vaccines fared when omicron was ascendant.
Infectious-disease experts say the study offers a thorough and up-to-date analysis of vaccine effectiveness, and can help researchers, doctors and policymakers better understand how the vaccines fared against omicron.
“This is such solid information that reinforces the current recommendation to get vaccinated and boosted—and [the vaccine] worked for omicron,” said William Schaffner, an infectious-disease specialist at Vanderbilt University Medical Center in Nashville, Tenn. who was not involved in the CDC report. “This is solid gold.”
Still, vaccine and booster effectiveness are known to wane after several months, as levels of neutralizing antibodies steadily decline. The latest data published by the CDC on death rates showed that unvaccinated people who became infected were nine times more likely to die than fully vaccinated people who had not received a booster, a drop from about 19 times more likely in early December. Unvaccinated people in January were 21 times more likely to die than people who got a booster shot, a drop from more than 60 times more likely to die in early December.
The study also found that protection against ventilation and death remained high regardless of which variant was dominant. Even when omicron caused a larger number of infections among those who had received shots, vaccinated and boosted individuals were far less likely to end up on ventilators or die.
“These vaccines will continue to prevent serious disease caused by the most dominant variant that’s out there today, which is omicron,” Schaffner said. “It is reassuring that all of these variants were well-protected by the vaccines.”
Experts say an additional booster shot could help curb the worst effects of the virus as immunity decreases over time, especially for older people and those with underlying health conditions or compromised immune systems. As concerns mount that a new variant called BA.2, a close cousin of omicron, could be gaining traction in the United States, some infectious-disease specialists say a second booster might keep hospitalizations and deaths lower.
“It wasn’t included in these studies, but nonetheless, every indication that we have is that the vaccines will continue to provide very, very good protection against serious disease, even against BA.2,” Schaffner said.