As members of the CDC’s Advisory Committee on Immunization Practices (ACIP) worked during the afternoon to organize its thoughts on deciding which groups could potentially receive a third dose of the Pfizer Inc.-Biontech SE COVID-19 vaccine, it heard more data about groups that had received the booster doses.

ACIP is in the first of its two-day deliberations for whether or not to recommend a booster dose of the vaccine for those ages 65 and older along with those at high risk for developing severe COVID-19. One of ACIP’s goals is identifying who belongs in the high-risk category.

Data from the CDC’s Vaccine Adverse Event Reporting System (VAERS) showed that 95% of participants had non-serious reactions and 5% had serious reactions not only to the Pfizer-Biontech vaccine but also to Moderna Inc.’s vaccine. Both are mRNA-based vaccines.

One case of myocarditis, an often-cited concern by ACIP members for those who may receive a booster,  was reported in VAERS, but it has yet to be adjudicated.

The most common solicited reactions report at least once in up to seven days after receiving a third dose of either vaccine were, in order, pain at the injection site, fatigue, myalgia, headache, fever, swelling at the injection site, join pain, chills, redness and nausea.

There were no unexpected patterns of adverse events identified in the data.

Beth Bell, clinical professor in the School of Public Health at the University of Washington, said ACIP should realize it can only make its deliberations and recommendations based on limited data. The group is not hearing about major gaps in the data at the moment, she said, but that could change substantively in a relatively short period of time.

Vaccination with a third dose would likely not eliminate transmission of the virus, said Matthew Daley, ACIP’s working group chair and a senior Investigator at Kaiser Permanente’s Institute for Health Research, but it is possible that the booster could at least decrease transmissibility.

Grace Lee, who chaired the ACIP group, said it made sense to possibly shift to a model like that used for the flu to provide recommendations that make sense for the larger population.

“The struggle is the balance to ensure safety of vaccines and access to vaccines as well as addressing and maintaining a focus on equity,” Lee added.

Keeping health care workers safe with a third dose, according to Helen Keep Talbot, an ACIP member who is an associate professor of medicine and an associate professor of health policy at Vanderbilt University, would help maintain necessary staffing levels.

Pablo Sanchez, a professor of pediatrics in the pediatric infectious diseases division of The Ohio State University-Nationwide Children’s Hospital in Columbus, Ohio, said he would argue that age is more important in receiving a booster instead of just who is at most risk of exposure. He added that he was not sure if anyone who has already had symptomatic COVID-19 should receive a booster.