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In trial, AstraZeneca 100% effective against severe cases, no raised clot risk

Drugmaker says long-awaited vaccine data shows 79% efficacy overall and that it works for all ages, including older people, as it seeks US FDA approval for emergency use

Medical staff administer the AstraZeneca vaccine at La Nuvola convention center in Rome, March 19, 2021. (AP Photo/Gregorio Borgia)
Medical staff administer the AstraZeneca vaccine at La Nuvola convention center in Rome, March 19, 2021. (AP Photo/Gregorio Borgia)

AstraZeneca said Monday that advanced trial data from a US study on its COVID vaccine shows it is 79% effective and does not present a specific risk of blood clots. Overall, the trial showed that the shot was 100% effective at preventing severe disease and hospitalization.

Although AstraZeneca’s vaccine has been authorized in more than 50 countries, it has not yet been given the green light in the US. The US study comprised 30,000 volunteers, 20,000 of whom were given the vaccine while the rest got dummy shots. The results were announced Monday.

In a statement, AstraZeneca said its COVID-19 vaccine had a 79% efficacy rate at preventing symptomatic COVID and was 100% effective in stopping severe disease and hospitalization. Investigators said the vaccine was effective across all ages, including older people — which previous studies in other countries had failed to establish.

The trial’s independent data safety monitoring board found no increased risk of thrombosis among the 21,583 participants who received at least one dose, the statement added.

A vial and syringes of the AstraZeneca COVID-19 vaccine, at the Guru Nanak Gurdwara Sikh temple, on the day the first Vaisakhi Vaccine Clinic is launched, in Luton, England, Sunday, March 21, 2021. (AP Photo/Alberto Pezzali)

The early findings from the US study are just one set of information AstraZeneca must submit to the Food and Drug Administration. An FDA advisory committee will publicly debate the evidence behind the shots before the agency decides whether to allow emergency use of the vaccine.

Scientists have been awaiting results of the US study in hopes it will clear up some of the confusion about just how well the shots really work.

“These findings reconfirm previous results observed in AZD1222 trials across all adult populations but it’s exciting to see similar efficacy results in people over 65 for the first time,” said Ann Falsey, professor of medicine at University of Rochester School of Medicine and co-lead principal investigator for the trial.

“This analysis validates the AstraZeneca COVID-19 vaccine as a much-needed additional vaccination option, offering confidence that adults of all ages can benefit from protection against the virus,” she added.

Midwives wait under medical supervision after receiving their first shot of the AstraZeneca COVID-19 vaccine in San Jacinto, eastern Guatemala, March 18, 2021. (AP Photo/Moises Castillo)

Britain first authorized the vaccine based on partial results from testing in the United Kingdom, Brazil and South Africa that suggested the shots were about 70% effective. But those results were clouded by a manufacturing mistake that led some participants to get just a half dose in their first shot — an error the researchers didn’t immediately acknowledge.

Then came more questions, about how well the vaccine protected older adults and how long to wait before the second dose. Some European countries including Germany, France and Belgium initially withheld the shot from older adults and only reversed their decisions after new data suggested it is offering seniors protection.

People rest after being vaccinated with the AstraZeneca COVID-19 vaccine in a mass vaccination site at the Brabanthal event center in Heverlee, Belgium, March 17, 2021. (AP Photo/Francisco Seco)

Last week, more than a dozen countries, mostly in Europe, temporarily suspended their use of the AstraZeneca shot after reports it was linked to blood clots. On Thursday, the European Medicines Agency concluded after an investigation that the vaccine did not raise the overall risk of blood clots, but could not rule out that it was connected to two very rare types of clots.

Britain’s Prime Minister Boris Johnson gestures after receiving the first dose of the AstraZeneca vaccine at St. Thomas’ Hospital in London, March 19, 2021. (AP Photo/Frank Augstein, Pool)

France, Germany, Italy and other countries subsequently resumed their use of the shot on Friday, with senior politicians rolling up their sleeves to show the vaccine was safe.

AstraZeneca said it was now preparing to submit its findings to the FDA to authorize the shot for emergency use.

“These results add to the growing body of evidence that shows this vaccine is well tolerated and highly effective against all severities of Covid-19 and across all age groups,” said Mene Pangalos, executive vice president of biopharmaceuticals R&D. “We are confident this vaccine can play an important role in protecting millions of people worldwide against this lethal virus.”

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