One dose of either Pfizer-BioNTech’s or AstraZeneca’s Covid-19 vaccine helps to prevent disease severe enough to require hospitalisation of people in their 80s with other illnesses, interim data from a UK study showed on Wednesday.

The findings, from an ongoing surveillance project funded by Pfizer and known as AvonCAP, found that one dose of the Pfizer-BioNTech shot, which began to be used in Britain on Dec. 8, 2020, was 71.4% effective from 14 days at preventing symptomatic illness severe enough to result in hospitalisation among patients with a median age of 87 years.

For the AstraZeneca vaccine, which began to be rolled out in Britain on Jan. 4, the results showed it was 80.4% effective by the same measures among patients with an average age of 88.

“These early results show the UK Covid-19 vaccine programme is working better than we could have hoped,” said Adam Finn, a professor of paediatrics and chief investigator of the AvonCAP study at Britain’s University of Bristol.

He said the findings showed how the vaccines can reduce the burden of serious Covid-19 in elderly, high-risk populations, and relieve pressure on health services.

The results add to other early findings from studies of vaccine roll-outs in Israel, Scotland and England, which have also pointed to high effectiveness from the first doses.

A UK study among healthcare staff found last week that a single dose of Pfizer’ vaccine cut the number of asymptomatic infections by about 75%, which would significantly reduce the risk of transmission of the virus.

A study in Israel, which last week confirmed an efficacy of well over 90% for Pfizer’s two-shot vaccine, also showed a single shot was 57% effective in protecting against symptomatic infections after two weeks.