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

  • U.S. moves to approve booster shots despite minimal evidence
    This week, the federal government announced that the U.S. intends to provide third vaccine doses to all Americans who received the Pfizer or Moderna vaccines. This booster shot distribution will start in September, with adults becoming eligible once they hit eight months after their second shot. Many epidemiologists, vaccine experts, global health experts, and other scientists have criticized the decision.
  • Three more COVID-19 data points, August 15
    A couple of additional items from this week’s COVID-19 headlines: children hospitalized with COVID-19, immunocompromised Americans now eligible for a third dose, and low cases linked to Lollapalooza.
  • The case for a moratorium on booster shots
    This week, the World Health Organization (WHO) called for wealthy nations to stop giving out booster shots in a push towards global vaccine equity. These nations should stall any booster shots until at least September, said WHO Director-General Tedros Adhanom Ghebreyesus at a press conference on Wednesday.
  • A dispatch from Provincetown, Mass.
    This week, I had the opportunity to talk to Mike, a Bear Week attendee from Pittsburgh, who caught COVID-19 in Provincetown. He told me about his experience attending parties, getting sick, and learning about the scale of the outbreak.
  • Vaccine requirements are the next big strategy
    After vaccine incentives largely failed to drive up vaccination numbers, government agencies and corporations alike are now opting for requirements. Hundreds of thousands of Americans learned this week that, in order to keep their jobs, they need to get their shots—or go through a more arduous process like weekly COVID-19 testing.

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