FDA approves COVID boosters, mixing vaccines; Swedish study says mixing vaccines is effective
Mix and Match
On Wednesday, October 20, U.S. regulators signed off on extending COVID-19 boosters to Americans who got the Moderna or Johnson & Johnson vaccine and said anyone eligible who is for an extra dose can get a brand different from the one they received initially.
These decisions from the U.S. Food and Drug Administration (FDA) signal a big step toward enlarging the U.S. booster campaign, which began with extra doses of the Pfizer vaccine last month. Before that happens, the Centers for Disease Control and Prevention will consult an expert panel before finalizing official recommendations for who should get boosters and when.
These actions would increase by tens of millions the number of Americans eligible for boosters and formally allow “mixing and matching” of shots — making it simpler to get another dose, especially for people who had a side effect from one brand but still want the proven protection of vaccination. The FDA authorized a third Moderna shot for seniors and others at high risk from COVID-19 because of their health problems, jobs or living conditions, six months after their last shot. Now the Moderna booster will be half the dose used for the first two shots, based on company data showing that was plenty to recharge the immunity again. For J&J’s single-shot vaccine, the FDA said all U.S. recipients, regardless of age, could get a second dose at least two months following their initial vaccination.
The FDA rulings differ, because the vaccines are made differently, with different dosing schedules. The J&J vaccine has consistently shown a lower level of effectiveness than the two-shot Moderna and Pfizer vaccines.The FDA said any brand can be used for the booster, regardless of which vaccination people got first. The interchangeability of the shots is expected to speed the booster campaign, especially in nursing homes and other institutional settings where residents have received different shots over time.
The FDA’s decision was based on preliminary results from a government study of different booster combinations that showed an extra dose of any type increases levels of virus-fighting antibodies. That study also revealed that recipients of the single-dose J&J vaccination had a far bigger response if they got a full-strength Moderna booster or a Pfizer booster rather than a second J&J shot. That study did not test the half-dose Moderna booster.
Health authorities emphasize that the priority still is getting first shots to about 65 million eligible Americans who remain unvaccinated. Nonetheless, the booster campaign is intended to increase protection against the virus because of signs that vaccine effectiveness is waning against mild infections, even though all three brands continue to protect against hospitalization and death.
FDA acting commissioner Dr. Janet Woodcock said, “The available data suggest waning immunity in some populations who are fully vaccinated. The availability of these authorized boosters is important for continued protection against COVID-19 disease.”
The Moderna booster decision effectively matches the FDA ruling that high-risk groups are eligible for the Pfizer vaccine, which is made with the same technology. FDA recommended that everyone who had gotten the single-shot J&J vaccine should get a booster, because it has consistently shown lower protection than its two-shot rivals. Several independent FDA advisers who backed the booster decision suggested that J&J’s vaccine should have originally been designed to require two doses.
Many experts continue to debate the rationale of the booster campaign. Some warn that the U.S. government has not clearly articulated the goals of boosters given that the shots continue to head off the worst effects of COVID-19. They question whether the objective is to tamp down on virus spread by curbing, at least temporarily, milder infections. Those questions are likely to be addressed when an influential panel convened by the CDC offers more specifics on who should get boosters and when. Their recommendations are subject to approval by the CDC director. The vast majority of the nearly 190 million Americans who are fully vaccinated against COVID-19 have received the Pfizer or Moderna options, while about 15 million have received the J&J vaccine.
Meanwhile, a Swedish study showed that mixing and matching different types of COVID-19 vaccines is highly effective, according to HealthDay News. The study showed that protection against infection was stronger in people who received a first dose of the AstraZeneca vaccine and a second dose of an mRNA vaccine than in those who received two doses of the AstraZeneca vaccine. The AstraZeneca vaccine is a vector-based vaccine, while the Moderna and Pfizer vaccines are mRNA vaccines.
Researcher Peter Nordström, professor of geriatric medicine at Umeå University in Sweden, explained, “Having received any of the approved vaccines is better compared to no vaccine, and two doses are better than one. However, our study shows a greater risk reduction for people who received an mRNA vaccine after having received a first dose of a vector-based, as compared to people having received the vector-based vaccine for both doses."
While previous research showed that mix-and-match vaccine schedules trigger a strong immune response, it was not clear whether that translated into a reduced risk of infection. Nordström and colleagues analyzed data from about 700,000 people in Sweden, where use of the AstraZeneca vaccine was halted for people younger than 65. People who had already received that vaccine as their first dose were advised to get an mRNA vaccine as their second dose. During an average follow-up of 2.5 months after a second dose, the risk of infection was 50 percent lower in those who received two doses of the AstraZeneca vaccine, 67 percent lower in those with a combination of the AstraZeneca and Pfizer vaccines, and 79 percent lower in those with a combination of AstraZeneca and Moderna, compared to unvaccinated people.
The researchers related that the Delta variant was dominant in Sweden during the study period. They also said that there were low rates of blood clots among all the vaccinated people in the study and that the number of COVID-19 cases severe enough to require hospitalization was too low to be able to calculate the effectiveness of the different vaccine combinations against this outcome.
According to study co-author Marcel Ballin, a doctoral student in geriatric medicine at Umeå University, "The results of the study may have implications for vaccination strategies in different countries. The World Health Organization has stated that despite the promising results from previous studies regarding immune response from mix-and-match vaccination, there is a need for larger studies to investigate their safety and effectiveness against clinical outcomes. Here we now have one such study."