AstraZeneca's COVID-19 shot was 79% effective in a trial involving 32,000 people, paving the way for authorization in the US despite troubles in Europe

• The COVID-19 shot from Oxford University and AstraZeneca was 79% effective in a large US trial.
• The vaccine was safe, and there was no evidence of blood clots in the US trial.
• AstraZeneca can now submit the data to the FDA seeking authorization for the shot.

The COVID-19 vaccine codeveloped by AstraZeneca and Oxford University was 79% effective at protecting against the novel coronavirus in the vaccine's largest trial yet, the drugmaker said Monday.

The vaccine was 100% effective at preventing severe COVID-19 and hospitalization, AstraZeneca said in a press release.

The drugmaker can now submit the data from the trial to be scrutinized by the US regulator, the Food and Drug Administration.

Sarah Gilbert, a professor of vaccinology who is the lead researcher on Oxford University's vaccine team, told BBC Radio 4 on Monday that it could take "some weeks" for the FDA's final decision.

The results come at a difficult time for AstraZeneca. The company is at the center of a political fight between the UK and the European Union over supply of the vaccine.

And in recent weeks, more than a dozen countries suspended use of its shot to investigate a so-far unsubstantiated link between getting the shot and developing blood clots.

The European regulator said Friday that the vaccine did not increase one's risk of clots overall but that it was further investigating reports of rare blood clots in the brain. Some European countries lifted their suspensions following the regulator's ruling.

In the US trial, the vaccine was found safe and there was no evidence of blood clots in the brain, which researchers specifically looked for.

AstraZeneca trial in US had 32,000 participants

The US trial tested AstraZeneca's two-dose shot to see whether it protected against symptomatic COVID-19, looking at cases that occurred at least 15 days after the second dose.

The trial included more than 32,000 participants over 18 years old across 88 locations in the US, Chile, and Peru.

The results are yet to be published in a peer-reviewed journal to be scrutinized by experts.

Existing coronavirus vaccines in the US from Moderna and Pfizer-BioNTech were roughly 95% effective at protecting against COVID-19 in trials of similar size in November.

The World Health Organization recommended AstraZeneca's vaccine for those over 18 years old on February 10. The shot is already authorized for emergency use in the UK, the EU, and several other countries.

COVAX, the World Health Organization's global initiative to ensure equal distribution of COVID-19 vaccines, said February 8 that it planned to distribute nearly 350 million doses of AstraZeneca's vaccine in the first half of the year. The vaccine is easier to store and distribute than those available from Moderna and Pfizer, which require colder temperatures.

It is also cheaper because AstraZeneca has said it will sell its vaccine without a profit throughout the pandemic.

The company said in November that it was making manufacturing capacity for up to 3 billion doses of the vaccine in 2021, on a rolling basis.

2 full doses, 4 weeks apart

The US trial was a less complicated design than previous trials run by Oxford and AstraZeneca.

Studies run out of the UK and Brazil found that the shot was 72% effective, on average, at protecting against symptomatic COVID-19. That figure was an average because the vaccine worked differently at different doses, with 62% efficacy when two full doses were given but 90% efficacy when the first dose was halved.

In the US trial, participants got two full doses of the vaccine.

Effective in older people

Gilbert told BBC Radio 4 on Monday that there was no drop in protection for older people and that it was "just as good" as for younger people.

Approximately 20% of trial participants were over 65 years old, according to the groups' press release.

There have been confusing rulings about its effectiveness in older people.

Germany, France, and others did not initially authorize it for people over 65, citing insufficient evidence in this age group, despite the European Medicines Agency's ruling that the vaccine was safe and effective.

Germany, France, and most other European countries have since backtracked.