Boosters provide 70% to 75% protection from Omicron: UK study

Covid vaccine boosters improve protection to as much as 75% against a rapidly spreading Omicron variant that is much more likely to bypass two doses than earlier strains, preliminary UK data shows.

The basic course of shots from AstraZeneca Plc and the Pfizer Inc-BioNTech SE partnership provided much lower defences against symptomatic infection with Omicron  compared with the Delta strain, the initial study showed. A booster lifted protection to 70% to 75% in the early days after the shot.

“These early estimates should be treated with caution, but they indicate a few months after the second jab, there is a greater risk of catching the Omicron variant,” said Mary Ramsay, head of immunisation at the UK Health Security Agency.

The findings come as the UK accelerates its booster campaign in the face of the heavily mutated variant. New evidence shows the strain is spreading much faster than Delta, and UK health officials expect Omicron to become the dominant variant there by the middle of December, accounting for more than half of new cases.

Effectiveness against severe disease is still unknown but expected to be higher than against symptomatic illness alone, the government said on Friday.

The UK has relied largely on the Pfizer vaccine for boosters, complemented by Moderna’s shot when needed. Many people in Britain got the AstraZeneca vaccine for their first two doses.

Preliminary study

The analysis looked at 581 people with confirmed Omicron, and health authorities said the figures should be interpreted with caution until more cases have been studied. 

The UK has moved to reimpose some measures, including indoor mask-wearing and work-from-home guidance, as Omicron proliferates. The new strain may be spreading faster in England than in SA and UK cases of the variant could top 60,000 a day by Christmas, according to epidemiologist John Edmunds.

Other early indications of vaccine effectiveness against Omicron have given a mixed picture, with Pfizer and BioNTech saying initial lab studies show a third dose may be needed to neutralise it. Researchers in SA have also found a drop-off in the level of antibody protection from that vaccine versus the new strain, though T-cells may still offer an immune defence against severe disease.

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