Omicron: AstraZeneca and Pfizer not very protective except after third dose

Omicron: AstraZeneca and Pfizer not very protective except after third dose

Studies on the Omicron variant increasingly tend to claim that it is resistant to current vaccines.

A study from the UK, pre-published Tuesday in the scientific journal MedRxiv, shows that the AstraZeneca vaccine “does not offer protection” after two doses and that the Pfizer BioNTech vaccine does offer ” limited protection ”. In both cases, the administration of a “boost” increases “considerably the protection”.

This study aimed to measure the effectiveness of the BNT162b2 (Pfizer BioNTech) and ChAdOx1 (AstraZeneca) vaccines against Omicron variant.

“We used negative test case controls to estimate vaccine efficacy against symptomatic disease caused by the Omicron and Delta variants in England. Assessments were made after two doses and after the third dose. ”

“The two-dose primary series of AstraZeneca provided no protection and two doses of Pfizer BioNTech provided limited protection against symptomatic disease against the Omicron variant,” said the experts. The study adds that administering a “boost” (third dose) with BNT162b2 (Pfizer BioNTech) significantly increased personal protection.

Among those who received two doses of Pfizer BioNTech, the vaccine efficacy was 88% 2 to 9 weeks after dose 2, but drops to 48.5% 10 to 14 weeks after dose 2 and falls further to 34%. and 37% 15 weeks after dose 2. Vaccine efficacy increased to 75.5% after the booster. Among those who received two doses of AstraZeneca, there was no protection against symptomatic disease with Omicron starting 15 weeks after the second dose. Two weeks after a booster dose of Pfizer BioNTech, the efficacy increases to 71.4%.

Extract from the study report

Against the Delta variant, the efficacy of the vaccine reached 41.8% after two doses received of AstraZeneca, but allowed to reach 93.8% two weeks after a third dose of Pfizer BioNTech. With two doses of Pfizer BioNTech, immunity is 63.5% then reaches 92.5% with a third dose.

The day before, the Minister of Health of Canada, Jean-Yves Duclos, asked that the vaccination for the third dose be done more quickly because “it is essential”, he said. Ontario has moreover got ahead of the other provinces and is preparing to offer this third dose to adults 18 years and over in its territory as of next Monday.

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