If an escape variant emerges, RNA vaccine makers such as Pfizer and Moderna could probably design and synthesize an initial prototype jab against it in a few days. Viral-vector vaccines, such as AstraZeneca’s, could follow closely behind. Making an RNA vaccine typically involves generating a new genetic sequence and encapsulating it in a fatty substance such as a lipid. Viral-vector vaccines are generated by inserting the key genetic sequence into a harmless carrier virus, culturing large quantities of the virus in a bioreactor, and purifying them.

But before these shots can be deployed, they will have to be tested in humans, and that will take time. So pharma companies are doing dry runs. Pfizer, with its partner BioNTech, based in Mainz, Germany, is testing a Beta-specific RNA vaccine in a randomized, placebo-controlled clinical trial with up to 930 participants. In August, the companies began a trial of a multivalent vaccine that targets both the Delta and Alpha variants.

“We’re not doing that because we actually think we need a new vaccine for those strains,” says Philip Dormitzer, vice-president and chief scientific officer of viral vaccines and mRNA at Pfizer, based in New York City. “We want to practise all aspects of executing a strain change — the preclinical research, the manufacturing, the clinical testing and the regulatory submissions — so that if we do see a variant out there that truly escapes vaccine immunity, we’re ready to go fast.” Dormitzer says Pfizer currently has no plans to deploy its Beta or Delta vaccines among the public.