Third dose and Omicron variant, efficacy drops after 10 weeks: report

The document from Great Britain: how Pfizer and Moderna booster doses work

The efficacy of the booster dose of the vaccine against symptomatic Omicron variant infections decreases by 15-25% after 10 weeks and declines more rapidly than in cases of the Delta variant. It is a passage from a report published in Great Britain by the United Kingdom Health Security Agency, the health agency. The document – which expressly refers to a partial framework and therefore must be interpreted “with caution” – was drawn up on the basis of the analysis of 147,597 cases related to the Delta variant and 68,489 associated with Omicron between 27 November and 17 December. The efficacy of the vaccine was observed among the cases linked to the 2 variants: these are subjects who had received 2 doses of Astrazeneca, Pfizer or Moderna in the ordinary vaccination course.

In all cases, the data showed that the efficacy of the vaccines against Omicron was found to be lower when compared to the results obtained in contrasting the Delta variant. Among those who were vaccinated with 2 doses of Astrazeneca, the booster dose – administered with Pfizer and Moderna – showed around 60% efficacy at 2-4 weeks post dose. After 10 weeks, it stood at 35% for Pfizer and 45% for Moderna.

Those who were vaccinated with 2 Pfizer doses and received the booster of the same drug, could count – according to the report – on an efficacy of around 70% which dropped to 45% after 10 weeks. With the Moderna booster, after 9 weeks the value remained around 70-75%.