Vaccine cocktails look viable—just in time for hot-vax summer

Some good global vaccine news this week: it looks like vaccine cocktails may be a promising option.

A clinical trial based in Spain of around 600 participants (aged 18-59) reported encouraging results regarding mix-and-match vaccines (or “heterologous prime-and-boost,” if you want the jargon) meaning one shot of one vaccine and the second shot of another. In this study, the first dose given was AstraZeneca, and the second was Pfizer. 

The study found that protective IgG antibodies were 30-40 times higher in the treatment group than the control group (those who had only received the first dose of the AstraZeneca vaccine). Neutralizing antibodies were also seven times higher after the Pfizer dose compared to the control, while usually they double in number after the second AstraZeneca shot. 

As some people familiar with Covid vaccines may note, these vaccines use two different mechanisms to stimulate the immune system: the AstraZeneca shot uses an adenovirus vector modified with the SARS-CoV-2 spike protein while the Pfizer vaccine uses messenger RNA to coax cells into making the spike protein themselves. This early success demonstrates that vaccines with different mechanisms can be combined to induce a strong immune response.

In the wake of the AstraZeneca blood clot news, it’s reasonable to expect that some may be hesitant to get the second shot if they have received the first AstraZeneca shot. Some authorities have advised people who have gotten the first dose of AstraZeneca to get an alternative for the second shot. Having an alternative that hasn’t been linked to blood clots might persuade those hesitant to get the second AstraZeneca shot to complete a vaccination regimen, especially if it might stimulate even more of an immune response than the regular AstraZeneca regimen.

There’s currently another heterologous prime-and-boost trial in place in the United Kingdom with a slightly more complicated experimental setup (the four groups were AstraZeneca for both shots, Pfizer for both shots, Pfizer for the first and AstraZeneca for the second, or vice versa), with all participants over 50. 

This study hasn’t reported results regarding immune responses yet, but they have reported some preliminary reactogenicity results. On May 12, researchers reported that mild side effects like fever or fatigue were more common in people who had received mixed vaccines. However, there were no severe side effects, and the mild ones subsided after a few days. The Spanish study did not find this, and instead found that mild side effects were about as common as they were with a regular vaccine regimen. 

The UK study is expected to report immune response data soon, so it’ll be interesting to see if it matches the results found by the Spanish study. We’ll keep you updated when those results come out.

More vaccine reporting

  • We failed to vaccinate the world in 2021; will 2022 be more successful?
    In January, COVAX set a goal that many global health advocates considered modest: delivering 2.3 billion vaccine doses to low- and middle-income countries by the end of 2021. is saying it’ll deliver just 800 million vaccine doses by the end of 2021, according to the Washington Post, and only about 600 million had been delivered by early December.
  • One month into vaccinations for kids 5-11, uptake varies wildly by state
    It’s been about a month since the FDA and CDC authorized a version of Pfizer’s vaccine for children ages five to 11. Those kids whose parents immediately took them to get vaccinated are now eligible for their second doses, and will be considered fully vaccinated by Christmas. Despite widespread availability of the shots, vaccine uptake has varied wildly.
  • Omicron updates: More transmissible, immune evading, but still not cause for panic
    We continue to learn more about this new variant as it spreads rapidly across the world, though much of the data are still preliminary. Here are a few major updates, including how vaccines fare against Omicron, its rapid spread, and more.
  • Cash incentives for vaccination have little impact
    While politicians at all levels have praised cash incentives, research has shown that this strategy has little impact on actually convincing Americans to get vaccinated. A recent investigation I worked on (at the Documenting COVID-19 project and the Missouri Independent) provides new evidence for this trend: the state of Missouri allocated $11 million for gift cards that residents could get upon receiving their first or second vaccine dose, but the vast majority of local health departments opted not to participate in the program—and a very small number of gift cards have been distributed thus far.
  • Vaccines aren’t enough: What Biden can do about Omicron
    This past Monday, President Biden said in a speech, “We’re throwing everything we can at this virus, tracking it from every angle.” Which I, personally, found laughable. The U.S.’s anti-COVID strategy basically revolves around vaccines, and it’s not sufficient for stopping new surges.

Leave a Reply