Following the White House administration’s announcement to start booster COVID-19 vaccinations for American adults in September, experts weighed in on the evidence for choosing an 8-month cutoff, how breakthrough infections figure in, and why calling one mRNA vaccine better than the other could be misleading.
Timing came up more than once at the Aug. 18 White House briefing announcing the booster plans. Reporters asked about the start time of Sept. 20 and people waiting at least 8 months after their second mRNA vaccine dose to get a booster.
Anthony Fauci, MD, chief medical adviser to the president and director of the National Institute of Allergy and Infectious Diseases, explained that late September gives the United States time to set up the logistics.
Centers for Disease Control and Prevention Director Rochelle Walensky, MD, MPH, added that 8 months is in part based on data from Israel and other countries on the waning of vaccine effectiveness over time.
“It is possible that 8 [months] is associated with the amount of time that we’ve been able to follow large groups of people, especially those who are 65 and older,” Julie Swann, PhD, said during a subsequent media briefing sponsored by Newswise on Aug. 18. “I know that Pfizer has said that they think a booster sometime between 6 and 12 months would be reasonable.”
Dr. Swann supported the administration’s booster shots plan. She said it is important “that we continue to get people the full amount of protection if it’s recommended by CDC and ACIP [Advisory Committee on Immunization Practices] that would come from a booster shot.” Dr. Swann is department head and A. Doug Allison Distinguished Professor at North Carolina State University and an adjunct professor in the joint department of biomedical engineering at the University of North Carolina at Chapel Hill.
Rising importance of breakthrough cases
Also on Aug. 18, news emerged that breakthrough cases are on the rise in seven U.S. states, likely because of the Delta variant.
These SARS-CoV-2 infections among the fully vaccinated account for 20% of cases in six of the seven states cited in a New York Times report, for example. Researchers also suggested that hospitalization and deaths associated with breakthrough cases could be higher than previously appreciated.
“It is expected that over time we will see more cases of Delta variant infections among vaccinated people. This points toward the need for booster vaccines and/or eventual modifications to the vaccine to capture new variants in the future,” Juan Wisnivesky, MD, DrPH, chief of the division of general internal medicine at Mount Sinai Health System in New York City, said during the briefing.
Vaccine comparisons unfair?
Following the release of a Mayo Clinic study reporting lower effectiveness of the Pfizer mRNA vaccine at 42% versus 76% for the Moderna product, some people started asking if one vaccine was better than the other.
“To begin with, the vaccines are not being compared side-by-side,” Dr. Wisnivesky said. “So we only know the effectiveness of each vaccine versus placebo, but we don’t know one versus the other.”
He added that different study designs, different populations, and other factors make direct comparisons difficult.
More evidence will be needed, Dr. Wisnivesky said, before public health officials can recommend that someone who received one mRNA vaccine switch to another for their booster shot.