Covid vaccine boosters improve protection to as much as 75% against the rapidly spreading omicron variant, based on preliminary U.K. data.
An early study of vaccine effectiveness showed that the shots from AstraZeneca Plc and the Pfizer Inc.-BioNTech SE partnership provided much lower defenses against symptomatic infection with omicron, compared with the delta strain, after two doses. A booster lifted protection to 70% to 75% in the early days after the shot.
U.K. health officials expect omicron to become the dominant variant by the middle of December. New evidence shows that the strain is growing much faster than delta in England and Covid cases caused by omicron are expected to make up about half of infections by the middle of the month, they said.
Effectiveness against severe disease is still unknown but expected to be higher than against any symptomatic illness, the government said Friday.
The U.K. has relied largely on the Pfizer vaccine for boosters, complemented by Moderna Inc.’s shot when needed. Many people in Britain got the AstraZeneca vaccine for their first two doses.
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 U.K. has moved to reimpose some measures, including indoor mask-wearing and work-from-home guidance, as omicron spreads rapidly through the country. The new strain may be spreading faster in England than in South Africa and U.K. 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 neutralize it. Researchers in South Africa have also found a drop-off in the level of antibody protection from that vaccine versus the new strain, though so-called T-cells may still offer an immune defense against severe disease.