Ross Clark Ross Clark

Does this Israeli study support Britain’s one-dose strategy?

(Photo: Getty)

Is the British approach of prioritising first doses of Covid vaccines and not promising a second dose until 12 weeks later compromising our ability to fight the disease? It is not a moot point, with several EU figures asserting that it is a risky route to take.

As I wrote here a couple of weeks ago, as far as the AstraZeneca/Oxford vaccine is concerned, what evidence we have supports the practice of delaying a second dose until 12 weeks after the first one; the vaccine is more effective that way.

However, a question mark has continued to hang over the Pfizer/BioNTech vaccine. There is limited data on the most effective dosing regime in this case because the phase 3 trials did not experiment with delayed doses – everyone involved was given a second dose 21 days after the first.

An Israeli study published in the Lancet, though, does now give us a better idea of the efficacy of the Pfizer vaccine after just one dose. The researchers administered first doses to 7,000 healthcare workers at the Sheba Medical Centre starting on 19 December, when Covid infections were raging in Israel. Within 28 days there were 170 cases of infection along the workers, of which 99 were symptomatic. Between days 1 to 14 after vaccination there were 5.5 infections per 1,000 person-days, falling to 3.0 between days 15 and 28. As for symptomatic infections, the rates were 2.8 and 1.2 respectively. Comparing this with unvaccinated healthcare workers in Israel, a single dose of the Pfizer vaccine was found to reduce all infections by 30 per cent between days 1 and 14, and 75 per cent between days 15 and 28. For symptomatic infections the efficacy rate was 47 per cent between days 1 and 14 and 85 per cent between days 15 and 28.

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