Just one dose of AstraZeneca’s COVID-19 vaccine is about 80% effective in preventing COVID-19 deaths in the elderly, according to a real-world analysis by Public Health England.

The impact resulted from a combination of the vaccine preventing infections and better survival among patients with a breakthrough infection after a single dose, the researchers said in the study, published preprint on Tuesday.

The research covered 50,000 Brits aged 70 or over and looked at the proportions who died within 28 days of receiving a positive SARS-CoV-2 test result.

People who had received one dose of the AstraZeneca vaccine were 55% less likely to die after infection than unvaccinated patients, while people with one dose of the Pfizer vaccine were 44% less likely to die.