The first large real-world study of how vaccines hold up against Omicron found that two shots of Pfizer Inc. and BioNTech SE’s Covid-19 vaccine lowered the risk of hospital admission by 70% for patients infected with the highly mutated variant.
The study, by South Africa’s largest private health insurer Discovery Ltd., found that while Omicron reduced vaccine effectiveness against infection to 33% from 80% for Delta, its effect on protection against hospitalization was less marked, falling to 70% from 93%.
While the study provides important clues about how vaccines hold up against Omicron, it is difficult to draw wide-ranging conclusions from South Africa, which has a much younger population than Europe and the U.S. and also has a different mix of immunity, with high levels of prior infection but a relatively low vaccination rate. For conclusions that may be more relevant for the U.S., health authorities will look closely at the U.K., whose demographic profile and vaccination rates are more like the U.S. and where the variant is already well established.
It comes as many governments rush to roll out booster shots more widely in the hope that—as early studies have suggested—a further shot will shore up protection against Omicron.
A growing number of studies indicate Omicron is more resistant to current vaccines than previous Covid variants, though boosters seem to help. WSJ’s Daniela Hernandez gets an exclusive look inside a lab testing how antibodies interact with Omicron. Photo illustration: Tom Grillo
“It’s very heartening to see this result and that we still have vaccine effectiveness [against hospital admission] that is still greater than 50%,” said Glenda Gray, president and chief executive officer of the South African Medical Research Council, which collaborated with Discovery.
The study examined 211,610 Covid-19 test results in adults reported since the beginning of September. It used that data to compare vaccine effectiveness during September and October, when Delta was dominant, with the three-week period between Nov. 15 and Dec. 7, when Omicron took hold. Discovery Health insures around 3.7 million people in South Africa.
The study—the largest to provide clues about how the vaccines hold up against Omicron in the real world—suggests that although the new strain can easily infect people who have been fully vaccinated, it is still much less likely to cause serious illness when it does. The research hasn’t yet been published or peer-reviewed in a scientific journal and scientists not involved in the research said the conclusions could change as more data emerges.
The Omicron variant was first identified by scientists in South Africa around three weeks ago and has driven a sharp rise in cases there. It has now been detected in 77 countries across the world, according to the World Health Organization. On Friday, scientists estimated Omicron’s R number in South Africa—a measure of how many people the average infected person goes on to infect—stood at 2.5, higher than any earlier variant.
New daily cases averaged 20,488 for the week ending Dec. 13, nearly double the week before. On Monday, in an indication that a large number of infections are being missed, health authorities said 31% of tests had registered a positive result.
The findings build on earlier, laboratory-based research from various groups around the world examining how well the blood of vaccinated people neutralizes the Omicron variant. Those studies found that antibodies in the blood of people who had received two doses of vaccine were much weaker against Omicron than earlier strains.
Last week, Pfizer executives predicted that the vaccines would hold up better against severe disease because the immune cells that fight the virus once it takes hold could still recognize most parts of Omicron’s spike protein, which the virus uses to enter cells.