Should You Combine Covid Vaccines?

Jano le Roux

Is it possible to acquire a COVID-19 vaccine from one company and then a booster from another? The matter has piqued the interest of medical professionals since the first shot was fired into a patient’s arm — and it’s far more than a purely academic issue. Allowing patients to mix and match COVID-19 vaccines could boost vaccine distribution and potentially provide medical advantages.
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The results from a recent National Institutes of Health research that aims to answer the issue will be reviewed by a Food and Drug Administration advisory committee. According to the first findings of this short study, the answer may be yes.

Doctors and pharmacists would also benefit, according to Robert M. Jacobson, medical director of the Mayo Clinic’s primary care immunization program. “Rather than having to turn some patients away, practitioners could just pick one brand to carry and know they could give that to anyone in the middle of their vaccine series,” he says. He points out that this would save waste by allowing more people to be inoculated from each open vial.

Scientific backing for mixing vaccines on a global scale would be especially beneficial to low-income countries, many of which lack national stockpiles. They’d be able to use any injections they got from relief organizations or contributions at the time. This is especially crucial given that only 2.5 percent of people in these nations have received even a single vaccination.

The focus rapidly moved to whether such mixing, referred to as a heterologous vaccination schedule in medicine, could provide immunological benefits. The researchers gave 830 patients either a double dose of the AstraZeneca or Pfizer-BioNTech vaccines four weeks apart, or a combination of the two, and all of them had an immune response over the threshold, indicating good protection.

People who had the AstraZeneca shot first, followed by the Pfizer shot, had the biggest reaction. Under this combination, the highest levels of antibodies (showing the body’s ability to combat the coronavirus) and T-cells (responsible for restricting the disease’s internal spread) were seen. Snape says he doesn’t sure which of these two immunological reactions is more essential. Researchers are still looking into whether the benefit lasts months after the shots; new blood samples collected six months after the initial doses are being evaluated right now, he says.

In this study, mixing vaccines caused somewhat more unpleasant reactions, but all of the observed side effects were minor headaches, fevers, and chills that went away within days. There were no combinations that prompted any safety concerns.

Although the AstraZeneca vaccine is not approved in the United States, many experts link it to the Johnson & Johnson vaccine since they both use a viral vector as a delivery strategy. An adenovirus, similar to those that cause the common cold, is used in both vaccines to transport a little bit of the SARS-CoV-2 virus’s genetic code into the body, causing an immune response.

The National Institutes of Health started its own mix-and-match study in June, and the preliminary results were released online on Wednesday. The FDA’s Vaccines and Related Biological Products Advisory Committee is currently reviewing them.

The researchers gathered 450 patients who had received the full series of any of the three vaccines approved in the United States. These participants had a booster shot at least three months later, either from the same brand or a new one. When the NIH researchers tested the patients’ blood for antibody levels 15 days after the booster, they discovered that mixing the shots improved their effectiveness, especially for those who had previously had the J&J jab.

Antibody levels rose 76-fold in the roughly 50 persons who used Moderna to augment their J&J vaccine, compared to just 4-fold in those who had another J&J vaccine. This group received a 35-fold increase in antibodies after receiving a Pfizer booster.

It was less dramatic to switch from one mRNA shot to another. Pfizer-Moderna beneficiaries received a 32-fold boost, while Pfizer-Pfizer recipients saw a 20-fold boost. The Moderna-Pfizer partnership turned out to be very similar to the Moderna-Moderna partnership. And no mRNA receiver had a greater boost from a J&J booster than they did from their original shot type.

If the results of this trial, as well as others already underway throughout the world, continue to show benefits, the CDC’s Advisory Committee on Immunization Practices (ACIP) may eventually approve a mix-and-match approach. However, at this time, it has not done so.

In the United States, the only combination procedure approved is for immunocompromised persons to receive a third mRNA shot to boost their normally inadequate response to the first two. The CDC encourages sticking with the same brand throughout, but if that isn’t possible, another mRNA vaccine can be used instead.

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