| AstraZeneca with Pfizer? J&J and Moderna? Some veterans of the pharma industry reckon you'll get stronger immunity to Covid with two different vaccine doses than with two of the same, and tried it out on themselves. Pierre Morgon crossed a border to do it, driving a couple of hours from his home in Lausanne, Switzerland, to a pharmacy in Lyon, France, for an Astra shot. He followed back in his home country almost eight weeks later with a dose of Moderna's. "If you prime the immune system with a certain technology, you get a broader, higher and more lasting response if you boost with something aiming at the same target but based on a different technology," says Morgon, a senior vice president at vaccine developer CanSino Biologics who also sits on the board of companies including Vaccitech and Univercells.  Pierre Morgon Photographer: Zornitsa Ivanova The approach is based on recent studies and years of research on mixing vaccines for diseases like Ebola, HIV and hepatitis. A study of almost 700 people in Spain showed that those who received a second dose of Pfizer's vaccine after a first Astra shot saw their neutralizing antibodies climb sevenfold, significantly higher than those who had two Astra doses. A much smaller trial in Germany recently suggested that mixing Astra and Pfizer shots could trigger antibody responses almost four times higher than a two-dose course of just the Pfizer vaccine. Bill Enright, chief executive officer of Vaccitech, which designed the technology behind the Astra vaccine, also took his regimen into his own hands. In Maryland, he got a J&J shot—intended as a one-shot regimen—before following up three months later with a Pfizer dose. Learning how to pair up vaccine types safely and effectively could be an important step toward solving global supply issues, allowing governments with scant stocks of multiple shots to mix and match. After concerns about rare blood clots arose regarding Astra's vaccine, a few European countries have already followed first doses of that vaccine with an mRNA version, like those made by Moderna and Pfizer. Still, the approach is unlikely to be approved formally for months, let alone encouraged. "Until a scheme is approved by authorities, it is a little bit experimental," said Morgon. "But we're not sorcerers. We're not playing with our lives here, we're applying existing science and our understanding of the coronavirus vaccines."—Todd Gillespie | 
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