- Health experts say more research is needed to determine if and how a mix-and-match vaccination strategy could be implemented going forward.
- Researchers recruited 830 volunteers who received one of the four combinations of vaccination.
- Antibody blood tests were done to determine how the mix-and-match vaccination strategy affected the participants’ immune responses.
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A new study from the United Kingdom found that mixing and matching doses of different coronavirus vaccines could potentially lead to a more robust immune response.
The research looked at antibody levels in people who received two doses of the Pfizer shot, two doses of the AstraZeneca shot, and one dose of Pfizer’s shot combined with one dose of the AstraZeneca-Oxford shot.
Two doses of the Pfizer vaccine produced the strongest antibody response.
One dose of AstraZeneca followed by one dose of Pfizer, and vice versa, generated a stronger antibody response than those who got two doses of AstraZeneca.
Meanwhile, some people vaccinated with the one-dose Johnson & Johnson shot are contemplating getting a second messenger RNA (mRNA) dose to better protect themselves against the delta variant.
But evidence shows that the J&J shot works well against all the variants, delta included, and health experts agree we need more research to determine if and how a mix-and-match vaccination strategy could be implemented going forward.
While the best course of action is to stick with the J&J shot or get two doses of the same vaccine, mixing doses may prove helpful for people who are immunocompromised.
“I think it is a promising line of research to do mix-and-match studies with vaccines that use different technologies. This can be something that can improve future vaccines and improve vaccine response in individuals who may not have an optimal response to traditional vaccine regimens,” Dr. Amesh Adalja, an infectious disease specialist and senior scholar at the Johns Hopkins University Center for Health Security, told Healthline.
Researchers recruited 830 volunteers who received one of the four combinations of vaccination — two Pfizer doses, two AstraZeneca doses, an AstraZeneca dose followed by a Pfizer dose, and a Pfizer dose followed by an AstraZeneca dose.
Researchers conducted antibody blood tests to determine how the mix-and-match vaccination strategy affected the participants’ immune responses.
They found that those who received both shots of the Pfizer vaccine had the strongest antibody levels, about 10 times higher than those who received two AstraZeneca doses.
Antibody levels were five times higher in people who got a Pfizer dose followed by an AstraZeneca dose than people who got both doses of AstraZeneca.
The volunteers who received an AstraZeneca dose followed by a Pfizer dose had antibody levels on par with the volunteers who received two Pfizer doses.
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Researchers are continuing to study how the mix-and-match strategy holds up over time.
For now, researchers recommend people stick with two doses of the same shot because clinical trials have shown that two doses provide strong protection against COVID-19 and the variants.
The “mRNA vaccines against SARS-CoV-2 have been shown to be very immunogenic in many studies. It is important to note that two-dose regimen with BNT, Pfizer vaccine is still the highest antibody group in this study,” Yildirim said.
There is growing concern that people vaccinated with the one-dose Johnson & Johnson shot may soon need a second dose of one of the mRNA shots, like Pfizer or Moderna, to enhance their protection against the delta variant.
But infectious diseases specialists say this isn’t necessary, at least not yet, as there is no data suggesting more breakthrough infections in people who got J&J shot than those who were vaccinated with an mRNA shot.
“There is no evidence that more breakthrough infections are occurring among J&J recipients,” Dr. Monica Gandhi, an infectious diseases specialist with University of California San Francisco, adding that data alone shows there doesn’t seem to be a need to boost the J&J shot.
New data published July 1 shows that the J&J shot works well against the variants, including delta.
The data also shows the immune response generated by the J&J shot appears durable, too, lasting at least 8 months.
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“There is no data that we need to boost the J&J with a Pfizer,” said Gandhi.
Scientists are still learning about how antibody levels correlate to protection against COVID-19.
“We don’t know at what level your antibodies are protective and under what level we should consider there is no protection either by the vaccination or after natural infection,” Yildirim said.
One thing is clear: The mixing-and-matching strategy needs to be further evaluated to determine the safety and potential benefits.
If mixing doses turns out to be both safe and more effective, it may provide more options for people who wish to get vaccinated.
“It appears that this is something that can increase immunity, and it’s something that may be useful in immunosuppressed populations or to design second-generation vaccines,” Adalja said.
“However, this is a research agenda not necessarily something that is to be implemented right now for everyone,” Adalja added.
In addition, mixing and matching doses may help combat supply-chain issues such as the ones we experienced earlier in the pandemic.
“Having different vaccines from different resources and producers and the option of using these vaccines in combination with other vaccines might reduce the impact of these shortages on the speed of vaccine roll-out in the future,” Yildirim said.
New research from the United Kingdom found that mixing and matching doses of different coronavirus vaccines could potentially lead to a more robust immune response. Health experts agree we need more research to determine if and how a mix-and-match vaccination strategy could be implemented going forward. If proven safe and effective, mixing doses could provide more vaccination options to immunocompromised people and help combat supply shortages.