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Pharmacists prepare to administer the AstraZeneca/Oxford Covid-19 vaccine at a temporary vaccination centre in Birmingham, England on Feb. 4, 2021.OLI SCARFF/AFP/Getty Images

Researchers in Britain have found that the Oxford-AstraZeneca vaccine is highly effective against the British variant of the virus that causes COVID-19, but scientists have yet to determine how well it works on other variants.

Preliminary findings released Friday showed that the vaccine was 74.6 per cent effective against the British variant, known as B.1.1.7. That was slightly less than the efficacy against the original version of the virus, which was 84 per cent, but researchers said the difference was not statistically significant.

“The important issue is that it’s in a very similar ballpark,” said Andrew Pollard, director of the vaccine group at the University of Oxford which helped develop the vaccine. “It’s a relatively small percentage difference. It’s still in the high 70s or 80s for both variants.”

The British variant first emerged in November in Kent outside London and is now the dominant version of the virus in the U.K. It has also spread to several other countries, including Canada. Studies have found that the variant is more deadly than the original version of the virus and it is up to 70 per cent more contagious.

Other drug makers have also been assessing their vaccines against the British variant but so far there have been few clinical trials. U.S. drug maker Novavax has been among the few companies to test its vaccine in trials, with early results showing that it was 85.6 per cent effective against the British variant – in line with its protection against the original virus. Laboratory testing on vaccines from Pfizer-BioNTech and Moderna have also found that both were effective against the variant.

However, so far most vaccines have not fared as well against the South African variant, which is also highly contagious. Novavax said clinical trials showed that its vaccine was 60 per cent effective against the South African variant. Johnson & Johnson said its vaccine was 72 per cent effective in the United States, 66 per cent in Latin America and 57 per cent in South Africa.

Dr. Pollard told a media briefing on Friday that a study was under way in South Africa to test the efficacy of the Oxford-AstraZeneca vaccine, with early results expected soon. Mene Pangalos, an executive vice-president at AstraZeneca, said he expected the findings to be comparable to other vaccines.

“We’re not going to be a surprised to see reduced efficacy because we’ve seen from the J&J vaccine and from the Novavax vaccine that these variants do impact, at least in mild and moderate disease, efficacy,” Mr. Pangalos told the briefing.

Canada has ordered up to 20 million doses of the Oxford-AstraZeneca vaccine, but Health Canada has yet to approve it.

The vaccine has run into controversy over how effective it is for people over the age of 65. There weren’t enough older people included in the clinical trials in Britain for researchers to determine the vaccine’s efficacy in the elderly, although AstraZeneca officials have said that further research has found the same antibody response. The company added that more data from U.S. trials will be available in the next month.

Regulators in Britain and the European Union have approved the vaccine for all ages but some European countries, including France and Germany, have recommended that it shouldn’t be used on people over 65. The vaccine has been in widespread use in the U.K. on all age groups since December and health officials said no one who has received a shot has been hospitalized or become seriously ill.

Dr. Pollard said it was up to each country to decide how to proceed. “The vaccine is authorized for emergency use across Europe in all ages,” he said Friday. “Each country has to make their own decision on which is the best approach for their population based on the supply of different vaccines.”

Earlier this week, Oxford researchers also found that the vaccine was 76 per cent effective for three months after the first dose. That backs up a decision by British health officials to delay the second dose of the vaccine by 12 weeks to allow more people to be vaccinated.

The report came as Britain’s drug regulator, the Medicines and Healthcare products Regulatory Agency, said the country’s massive vaccination program has turned up few safety concerns.

Britain has inoculated more than 10 million people with the Pfizer-BioNTech and Oxford-AstraZeneca vaccines. In a report released Friday, the MHRA said there had been 22,820 reports of suspected side effects, or an overall rate of three reports for every 1,000 shots. Most of the side effects were sore arms, headaches, fatigue, fever and aching muscles.

“Generally, these happen shortly after the vaccination and are not associated with more serious or lasting illness,” the report said. “These types of reactions reflect the normal immune response triggered by the body to the vaccines.”

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