A third dose of the AstraZeneca Covid-19 vaccine significantly boosted neutralising antibodies against omicron, according to lab studies at the University of Oxford.
The vaccine, created by Astra and Oxford, saw antibodies increase to similar levels as those after two doses against the Delta variant with a booster shot, the drug company said Thursday.
A third dose also produced higher levels of neutralising antibodies than those found in individuals who had recovered naturally from the Alpha, Beta and Delta strains.
The results are largely good news for the vaccine, which has been sidelined in the West as a booster after messenger RNA vaccines were shown to be more effective in various trials. The study looked at 41 people who had been given a third dose.
Omicron’s rapid spread and its ability to initially reduce antibody protection in many vaccines led a number of countries to launch accelerated booster campaigns. The UK alone reported more than 100,000 new covid cases Wednesday for the first time.
Some vaccines haven’t fared so well in the face of the new variant. Two doses and a booster of the Covid-19 vaccine made by China’s Sinovac Biotech, one of the most widely used in the world, didn’t produce sufficient levels of neutralising antibodies to protect against Omicron, according to lab test results published Thursday.
The research suggests that people who’ve received Sinovac’s shot, known as CoronaVac, should seek out a different vaccine for their booster.
Omicron severity
Early studies out of South Africa, Scotland and England show the highly mutated Omicron variant appears less likely to land patients in the hospital than Delta. The findings raise hopes there will be fewer cases of severe disease, yet Omicron’s greater infectiousness means it could still severely affect health services, fuelling the need for boosters.
According to a preprint of the Astra study, neutralising antibodies against Omicron were only 3.6-fold lower 28 days after a booster Astra shot compared with the levels seen from three shots against Delta. Still, the shot overall didn’t perform as well as the one from Pfizer and BioNTech.
Neutralisation titres against Omicron increased 2.7-fold after a third Astra shot, compared with 34.2-fold for Pfizer, when measured against antibody levels 28 days after a second dose of each of the shots.
“It is very encouraging to see that current vaccines have the potential to protect against Omicron following a third dose booster,” said John Bell, a professor of medicine at Oxford and one of the study investigators. “These results support the use of third dose boosters as part of national vaccine strategies, especially to limit the spread of variants of concern, including omicron.”
Pfizer study
The results come after Pfizer and Moderna released studies on how their vaccines stand up against Omicron in recent weeks.
Initial lab tests from Pfizer showed a third dose of their Covid-19 vaccine may be needed to neutralise Omicron after researchers observed a 25-fold reduction in neutralising antibodies that fight the variant from two doses.
Moderna also found a booster dose increased antibody levels against Omicron.
Novavax said Wednesday that its vaccine generates an effective immune response against the variant, but added it could be necessary to develop an Omicron-targeted vaccine.
Data from another lab study showed two doses Astra’s retained some protection against Omicron, although a 36-fold decrease in antibody levels was observed from the original virus strain.
