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COVID Vaccine Makers Prepare for a Variant Worse than Delta

Pfizer’s chief executive, Albert Bourla, made a bold promise in June. Standing next to US President Joe Biden at a press conference in St Ives, UK, just before the G7 summit meeting, Bourla said that should the need arise for a new COVID-19 vaccine, his company could get one ready within 100 days.

The need he was referring to is the possible emergence of an ‘escape variant’ — a dominant strain of SARS-CoV-2 that evades the fledgling immunity established through vaccines and previous infections. No such strain has yet been identified, but Pfizer and other leading COVID-19 vaccine makers are gearing up for that scenario.

What does it take to be nimble enough to design and test an updated vaccine against an unknown viral strain, in record time? Nature spoke to three COVID-19 vaccine makers — Pfizer, Moderna and AstraZeneca — to find out exactly how they are preparing.

Over the past few months, all three companies have been running dress rehearsals by practising on known SARS-CoV-2 variants. This involves updating their vaccines to match variants such as Beta and Delta, testing them in clinical studies, tuning their internal workflows and coordinating with regulators. Their goal is to learn from these warm-up trials and smooth out kinks in their processes, so that they can move fast if, or when, a true escape variant emerges.

“At some point, inevitably, we’re going to have to make variant vaccines — if vaccines are the way population immunity will be maintained — but we’re not at the point where we can confidently predict the evolution of the virus,” says Paul Bieniasz, a virologist at the Rockefeller University in New York City. “Practising with existing variants seems like a reasonable approach.”

The first generation of COVID-19 vaccines seems to be holding up against Delta and other known variants, at least in preventing severe disease and hospitalization. Pfizer, Moderna and AstraZeneca say that their vaccines, which are based on the original SARS-CoV-2 strain that was first detected in Wuhan, China, still offer the best protection against all known variants. “There really isn’t a need at this time to make a new vaccine that will be more effective, because it looks like the old ones work very well [against] the Delta variant,” says Kathryn Edwards, scientific director of the Vanderbilt Vaccine Research Program.

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