Delaying second Covid vaccine doses can save lives, study finds

Delaying the second dose of the Pfizer/BioNTech or Moderna vaccines as the UK has done can save lives, according to a US modelling study that suggests other countries struggling to immunise their populations could adopt the strategy.

Second shots of both vaccines and the Oxford/AstraZeneca jab are designed by the manufacturers to be given within three to four weeks of the first dose. The UK, however, opted for a 12-week delay between doses in a bid to ensure that more people received their first vaccination more quickly.

Immunological evidence has shown high protection from one dose – up to around 80% with both Pfizer and Moderna, which are both mRNA vaccines made in a similar way. There is also evidence from the UK’s immunisation programme that people given a single dose of the AstraZeneca and Pfizer vaccines are unlikely to be admitted to hospital with Covid.

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The US study, from scientists at the Mayo Clinic in Rochester, models the effect of delaying second doses of the Pfizer and Moderna vaccines – the two used in the US – in populations where the vaccine rollout is slow because of global shortages.

They found that getting a single dose to more people by delaying the second shot would save lives. In people under 65, where the vaccine efficacy is 80% and only 0.1% to 0.3% of the population a day is vaccinated, between 47 and 26 deaths per 100,000 people could be averted, they say in their paper in the British Medical Journal.

Dr Peter English, a retired consultant in communicable disease control, said the study demonstrated that delaying the second dose worldwide would control the disease most quickly and prevent emerging variants from affecting every country.

“So we all have a vested interest in ensuring that the whole world is vaccinated as soon as possible,” he said. “This paper supports that view. It raises questions about, for example, the proposed third-dose [second booster] apparently planned for the UK in autumn 2021. It might be in the UK’s interests, as well as global interests, for those doses to be used in countries where they are needed more.”