April 21, 2022 -- The CDC is considering what to tell the public about second booster shots with mRNA vaccinations for COVID-19.

The US Food and Drug Administration (FDA) in March authorized a second booster dose of either the Pfizer-BioNTech or the Moderna COVID-19 vaccines for people aged 50 and older and certain immunocompromised adults, even though many top infectious disease experts questioned the need before the agency's decision.

In a Wednesday meeting, the CDC asked its Advisory Committee on Immunization Practices (ACIP) to discuss second booster shots, but did not ask the group of experts to vote on formal recommendations.

Instead, the experts talked about the potential timing of additional COVID-19 vaccines for those who already have had three shots, and challenges for vaccination efforts that likely will arise as the pandemic persists.

ACIP member Beth Bell, MD, MPH, of the University of Washington, said she's concerned about the potential for "booster fatigue."

"A vaccination program that's going to require boosting large proportions of the population every 4 to 6 months is really not sustainable and probably not something that most people want to participate in," she said.

The benefit of additional COVID-19 shots for now appears to be smaller than what people get from the initial doses, Bell said.

Earlier in the meeting, CDC staff presented estimates about how well the COVID-19 vaccines work to prevent one case of hospitalization from the disease over 4 months among people aged 50 and older.

The major gain in preventing hospitalizations occurs with the first vaccination series and then wanes, the CDC said.

It appears that one hospitalization is prevented for every 135 people who get the first round of COVID-19 vaccinations. But it takes 674 people getting a first booster dose to prevent one hospitalization. A second booster prevents one hospitalization for every 1205 people vaccinated.

Bell said she's concerned about considering additional doses for "smaller and smaller return and creating an impression that we don't have a very effective vaccination program," even though the CDC's data show a clear benefit.

Reasons to Get a Second Booster

Elisha Hall, PhD, RD, of the CDC presented slides with some factors to help determine the urgency for a person to get a second booster:

  • Having certain underlying medical conditions that increase the risk of severe COVID-19 illness
  • Being moderately or severely immunocompromised
  • Living with someone who is immunocompromised, at increased risk for severe disease, or who cannot be vaccinated because of age or contraindication
  • Being at increased risk of exposure to SARS-CoV-2, the virus that causes COVID-19, such as through occupational, institutional, or other activities (eg, travel or large gatherings)
  • Living or working in an area where there is a medium or high level of COVID-19 in the community

In contrast, people might want to wait if they had been infected with SARS-CoV-2 within the past 3 months, Hall said in her presentation. Another reason for delay might be a concern that a booster dose may be more important later in the year.

The experts also addressed public confusion over boosters. For the Pfizer and Moderna mRNA vaccines, a second booster is a fourth dose, but for those who received the one-shot J&J vaccine, the second booster is a third dose.

Going forward, it may be easier to refer to subsequent doses as "annual boosters," the CDC's Sara Oliver, MD, MSPH, told the panel. It will be important to keep language about subsequent vaccinations clear and easy for the public to follow, she said.

Oliver also said there's already been a drop-off in the acceptance of second rounds of COVID-19 vaccinations. CDC data show that 77% of people in the US have had at least one dose of a COVID-19 vaccine, but only 66% of the population is fully vaccinated, and only 45% have had a first booster dose.

In her presentation, Oliver said the top priority in COVID-19 vaccination efforts remains initial vaccinations for people who haven’t gotten them.

Kids Younger Than 5

During the public comment session of the CDC meeting, several people called on the FDA to move quickly to expand authorization of COVID-19 vaccines to children aged 5 years and younger.

"We know that many parents and caregivers and healthcare providers are anxious to have COVID vaccines available" for young children, said Doran Fink, MD, PhD, a deputy director of the FDA's vaccines division.

He said the agency is working to be ready to authorize the shots for young children while it awaits research results from the manufacturers.