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December 2, 2021

Health Officials Say People Can “Mix & Match” COVID Vaccines

Health Officials Say People Can “Mix & Match” COVID Vaccines

The U.S. Food and Drug Administration (FDA) has authorized boosters of all three COVID-19 vaccines: Pfizer-BioNTech, Moderna, and Johnson & Johnson (J&J). And health officials are urging all fully vaccinated adults to get one once they’re eligible amid an uptick in new cases nationwide and the emergence of the worrisome Omicron variant.

The FDA also used its authority to allow people to mix-and-match, giving adults who are fully vaccinated against COVID-19 the freedom to choose which vaccine they’d like to receive as their additional dose.

So, if you got the Johnson & Johnson shot at least two months ago, you could get a booster dose of either the Pfizer or the Moderna mRNA vaccine, or if you got fully vaccinated with the Pfizer shot at least 6 months ago, you can choose to get a Moderna shot as your booster dose. And so on.

The ability to mix and match COVID-19 vaccines offers people more flexibility in getting additional vaccine doses based on what’s available in their local area.

So, which one is best?
One vaccine isn’t recommended over another. Research on that is ongoing. But so far, there is a growing body of evidence, which suggests that mixing and matching is safe and produces as many or more antibodies as getting the same vaccine as a booster.

In a preliminary mix-and-match study conducted by the U.S. National Institutes of Health (NIH) that has not yet been published or peer-reviewed, fully vaccinated people who got any of the three available COVID vaccines were given a booster dose of either the Moderna, Pfizer-BioNTech, or J&J vaccine. Overall, there were total of nine different combinations.

The NIH study found that found that people who originally got the Moderna two-dose series and then received any company’s booster saw the biggest increases in neutralizing antibodies against the coronavirus.

But those who got the Moderna booster were given a full dose booster—not a half-dose, which is what has been authorized by the FDA.

The lowest rise was seen in people who got J&J’s vaccine for their initial dose as well as their booster. Those who got the J&J vaccine had a more robust immune system response if they got a booster dose of one of the mRNA vaccines—either Pfizer or Moderna.

But these results must be taken with a grain of salt, because the study was designed to show whether mixing and matching vaccines is safe and effective—not identify which combination is “best.” Overall, no matter which type of vaccine people got initially and as a booster, antibody levels increased, the study showed.

Looking ahead, large, randomized controlled trials are needed to determine which of the nine mix-and-match combinations provided the greatest protection for various age and risk groups. More research is also needed to examine how long immunity following boosters lasts over time.

Remember, antibodies aren’t everything
Antibodies levels, which were investigated in the NIH study, are only one measure of immunity against the coronavirus. The body has other ways of defending itself.

Unlike the innate immune system, which launches a general attack to invading pathogens, the body also has an adaptive, or acquired immune system, which includes two types of cells that learn from experience: T-cells and B-cells. B-cells are antibody factories, while T-cells support B-cells and kill virus-infected cells outright.

Antibody levels may fall after infection. But T-cells and B-cells that the immune system deployed to fight off the infection (or that a vaccine has taught the body to make) can be stored by the immune system for years, where they remain ready to do battle if the virus ever returns.

Sources:
Centers for Disease Control and Prevention. “CDC Expands COVID-19 Booster Recommendations.” Nov 29, 2021.
U.S. Food and Drug Administration. Coronavirus (COVID-19) Update: FDA Takes Additional Actions on the Use of a Booster Dose for COVID-19 Vaccines. Oct 20, 2021.
Centers for Disease Control and Prevention. "CDC Statement on ACIP Booster Recommendations." Sep 24, 2021.
U.S. Food and Drug Administration. “FDA Authorizes Booster Dose of Pfizer-BioNTech COVID-19 Vaccine for Certain Populations.” Sep 22, 2021.
Centers for Disease Control and Prevention. "Media Statement from CDC Director Rochelle P. Walensky, MD, MPH, on Signing the Advisory Committee on Immunization Practices’ Recommendation for an Additional Dose of an mRNA
COVID-19 Vaccine in Moderately to Severely Immunocompromised People." Aug 13, 2021.
Centers for Disease Control and Prevention. “ACIP Data and Clinical Considerations for Additional Doses in Immunocompromised People.” Jul 22, 2021.
U.S. Food and Drug Administration. “Coronavirus (COVID-19) Update: FDA Authorizes Additional Vaccine Dose for Certain Immunocompromised Individuals.” Aug 12, 2021.
Atmar RL, Lyke KE, Deming ME, et al. Heterologous SARS-CoV-2 Booster Vaccinations – Preliminary Report (preprint). medrXiv. Posted Oct. 13, 2021.
Bar-On YM, Goldberg Y, Mandel M, et al. Protection Across Age Groups of BNT162b2 Vaccine Booster against Covid-19 (preprint). medrXiv. Posted Oct. 7, 2021.
Chiu NC, Chi H, Tu YK, et al. “To mix or not to mix? A rapid systematic review of heterologous prime-boost covid-19 vaccination.” Expert Rev Vaccines. Sep 2021.
Schmidt T, Klemis V, Schub D,et al. “Immunogenicity and reactogenicity of heterologous ChAdOx1 nCoV-19/mRNA vaccination.” Nat Med. 2021 Sep;27(9):1530-1535.
Merck Manual. “Overview of B- and T-Cell Function.” Accessed Oct 19, 2021.

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