The global recovery is under threat. The super-infectious Delta variant has spread fast. So efforts from top vaccine makers BioNTech and Pfizer to stay ahead of the mutations are timely. As well as planning a trial of Delta variant vaccine in August, they argue that a third dose of the existing vaccine “may be beneficial” to maintain the highest levels of protection.

It would certainly benefit the companies’ bottom lines. Booster shots would prolong the windfall, expected to generate at least $26bn in sales this year. After a 50 per cent gross profit split with BioNTech, Pfizer is in line for a profits boost of $7bn or more.

Yet the need for such additional shots is debatable, particularly given the worldwide shortage of jabs. The UK is planning an autumn booster campaign but scientists advising the US public health agency found insufficient data to support such a move.

A double dose remains effective at keeping people out of hospital. True, an Israel study found the jab was only 64 per cent effective at protecting against infection from the variant, compared with 94 per cent for previous strains. But it is not conclusive. Other studies suggest this vaccine is substantially more effective, says Dr Anthony Fauci, Joe Biden’s chief medical adviser.

There is, to be sure, a need for more protection for vulnerable groups, like cancer patients and others with compromised immune systems. As well as boosters, the antibody cocktails produced by the likes of US biotech Regeneron may have a role. Their prospects were dimmed by the success of vaccines, but they have the potential to gain blockbuster status as a preventive drug.

New evidence could tip the balance in favour of boosters for the population at large. Delta is almost twice as infectious as the original strain. A risk of overwhelming the healthcare system remains, even where high vaccination rates have weakened the link between cases and hospitalisations. Further, there is a real possibility that the vaccine’s protection does not last as long against variants like Delta. Politicians weighing up the case for boosters may prefer to be safe, not sorry.

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