CDC advisory committee unanimously recommends booster shots of Pfizer and Moderna’s Covid vaccines

By Mary Kekatos, American Health Editor for

What are COVID-19 vaccine boosters?

A booster shot is given at least two months after people have been fully vaccinated against COVID-19.

It is intended to prolong immunity and ‘boost’ the immune system to make higher levels of antibodies against the virus.

Is vaccine protection waning?

Several studies have recently suggested that vaccine protection diminishes over time.

A recent study by the Public Health Institute in Oakland, California, found that the overall effectiveness of the three Covid vaccines available in the US fell from 87% in March to 48% in September.

Johnson & Johnson’s vaccine saw its protection decline the most, falling from 86% in March to below 50% in September and to just 13% in October.

The Pfizer-BioNTech shot saw its effectiveness drop from 87% in March to 43% in September.

Moderna’s shot held up the best, but still fell from 89% in March to 58% in September.

However, health officials insist that vaccines are still highly effective against the most serious effects of COVID-19, including hospitalization and death.

In addition, some people have weakened immune systems, either due to medical conditions or age, making them unable to mount a full immune response to the first doses.

Who is currently eligible?

All U.S. adults 18 years and older who are fully vaccinated can receive a booster shot.

The first group to be allowed to receive boosters were Americans with compromised immune systems, and that decision came in August.

Subsequently, the US Food and Drug Administration (FDA) extended that authorization to specific risk groups.

These include people aged 65 and over, residents of long-term care facilities, and people aged 18 to 64 who are at high risk for severe COVID-19 due to underlying medical conditions.

Also authorized are those who are at high risk because of their job or other factors, such as health professionals, teachers and grocery store workers – and those who live in institutional settings that increase their risk of exposure, such as prisons or shelters for the homeless.

In November, this authorization was extended to all adults regardless of risk factors for serious disease.

Which COVID-19 vaccine booster can I get?

Americans can get any of the three authorized boosters.

Pfizer-BioNTech and Moderna booster shots are administered at least six months after the last injection.

J&J’s booster injection is given at least two months after the last dose.

The Pfizer and J&J booster shots are exactly the same — both in ingredient and dosage (30 micrograms and 0.5 milliliters, respectively) — as the primary doses.

Moderna’s booster injection is 50 micrograms – half the dosage of the original vaccine.

Can I mix and match?

Yes, federal health officials say Americans can get booster shots made by a different vaccine manufacturer than their initial doses.

Researchers from the National Institutes of Health presented data at an October meeting of the FDA advisory committee demonstrating the effectiveness of mixing and matching.

The report found that when recipients of the single J&J vaccine received a second dose, their antibody levels increased fourfold in two weeks.

In comparison, when given a Moderna booster, their antibody levels rose 76-fold over the same period.

A booster shot of the Pfizer vaccine also increased antibody levels 45-fold over the course of two weeks — higher than the J&J shot, but not as high as the Moderna shot.

In addition, the Moderna booster was also found to increase antibody levels in higher Pfizer recipients.

Americans who received two doses of the Pfizer saw their antibody levels increase 21-fold after a third injection of Pfizer.

But those who received the Moderna booster had a 32-fold increase in antibody levels over a 14-day window.