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AstraZeneca Plc’s COVID vaccine showed 82 per cent effectiveness with a three-month gap between two shots, according to a new study that bolsters the U.K.’s controversial decision to adopt an extended dosing interval.
The vaccine may also significantly reduce transmission of the virus, according to analysis of trial data by the University of Oxford, which developed the shot with the British drugmaker. Swabs taken from volunteers in the U.K. arm of the trial showed a 67 per cent reduction in transmission after the first dose, the report showed.
The U.K. approved giving the first and second injections of two-shot vaccines from four to 12 weeks apart in an effort to stretch scarce supplies while manufacturing is ramped up. AstraZeneca executives had previously said the longer gap, compared with the three- to four-week period between shots that’s been recommended for other vaccines, could also boost effectiveness.
The new results are a further boost for the immunization program in the U.K., which has raced ahead of countries in the European Union and has given initial shots to 14 per cent of residents. If the Astra vaccine also reduces transmission, it will speed up the process of achieving herd immunity, when the virus can no longer make inroads into a population. The effect on asymptomatic transmission fell after the second shot to 50 per cent, the report showed.
“Extending the dosing interval not only boosts the vaccine’s efficacy, but also enables more people to be vaccinated upfront,” said Mene Pangalos, Astra’s executive vice president for biopharmaceuticals research, in a statement. “Together with the new findings on reduced transmission, we believe this vaccine will have a real impact on the pandemic.”
AstraZeneca shares rose 0.5 per cent early Wednesday in London.
Vaccine efficacy rose from 55 per cent with a dosing interval of less than six weeks to 82 per cent when spaced 12 or more weeks apart, according to new data. The analysis also found the shot showed 76 per cent protection after the first of two injections. That level of immunity was achieved from 22 days after the first shot.
Questions have swirled around the AstraZeneca vaccine since the company reported early trial results that showed 70 per cent protection, on average. Those results came from two subsets, one of which delivered 62 per cent effectiveness, the other 90 per cent, with the higher level coinciding with a mistake in dosing. When the U.K. approved the vaccine in December, regulators signaled that they thought the discrepancy was more likely linked to the interval between shots than the dosing level.
The initial results were based on 131 cases of symptomatic COVID-19 in the trials, a number that has since grown to 332, allowing for more in-depth analysis. The new data are based on information from more than 17,000 trial participants in the U.K., Brazil and South Africa, Oxford said.
The European Union has also approved the vaccine, with France, Germany and some other countries restricting its use in the elderly, citing a lack of trial data in older age groups.
“These new data provide an important verification of the interim data that was used by more than 25 regulators,” said Andrew Pollard, chief investigator of the Oxford trial and co-author of the paper, in a statement. It also supports the policy recommendation made by the U.K. vaccine advisory panel, he said.
Oxford is also planning to publish data on how the vaccine interacts with new variants of the coronavirus in coming days. The university said it expects the findings to be in line with those from other developers.
Moderna Inc. said last month its vaccine will protect against two known coronavirus variants, but it plans to start human studies of a booster shot for a strain from South Africa that may cause immunity to wane more quickly. Pfizer Inc. is also looking to develop a booster shot.
--With assistance from Stephanie Baker.