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New research: 4th dose gives extra protection from severe Covid-19, study finds

Rates of confirmed SARS-CoV-2 infection and severe Covid-19 found were lower after a fourth dose than after only three doses.

A 85-year-old man receiving a booster vaccination in central Frankfurt. (AP Photo/File)

Studies on various vaccines globally have shown that an additional dose provides extended protection against Covid-19. Now, a study from Israel has found that four doses offer greater protection against severe disease than three, but the protection against infection itself was brief. India has started rolling out a ‘precautionary’ (third) dose for the general population.

ISRAEL DRIVE: Israel began giving the fourth dose to citizens over age 60 on January 2 this year. The vaccine in use there, from Pfizer BioNTech, uses the mRNA platform (in India, the two main vaccines, Covishield and Covaxin, use different platforms). The study, conducted between January 10 and March 10 when the Omicron variant was predominant, has been published in The New England Journal of Medicine.

The researchers used Israeli Health Ministry data on 12.5 lakh persons aged 60 or older. It estimated the rate of confirmed infection and severe Covid starting at 8 days after the fourth dose, compared with the rate among persons who had got only three doses, and among persons who had received a fourth dose 3 to 7 days earlier.

FINDINGS: Rates of confirmed SARS-CoV-2 infection and severe Covid-19 found were lower after a fourth dose than after only three doses. Protection against confirmed infection appeared short-lived, but protection against severe illness did not wane during the study period.

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The unadjusted number of cases of severe Covid-19 per 100,000 person-days was: 1.5 in those who got four doses, 3.9 in those who got three doses, and 4.2 in the internal control group (fourth dose 3 to 7 days earlier). When adjusted, the rate of severe Covid in the fourth week after the fourth dose was lower than that in the three-dose group by a factor of 3.5, and was lower than that in the internal control group by a factor of 2.3.

Protection against severe illness did not wane during 6 weeks after the fourth dose. The adjusted rate was lower than in the three-dose group by a factor of 2.0 and was lower than that in the internal control group by a factor of 1.8. But this protection waned in later weeks, the study said.

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First published on: 16-04-2022 at 04:00 IST
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