LONDON – A further U.K. real-world study of COVID-19 vaccines has found a single dose dramatically reduces the chances of the most elderly and frail being admitted to the hospital as a result of serious infection.

The study covers every person over 80 years of age admitted to one of two hospitals in Bristol with acute respiratory disease, from Dec. 18, 2020, 10 days after the U.K.’s COVID-19 vaccination program began, to Feb. 26, 2021.

Comparing the immunization rates between patients who had a positive test for SARS-CoV-2 on hospital admission, and of controls whose tests were negative, the effectiveness of one dose of either the Pfizer Inc./Biontech SE or Astrazeneca plc vaccines has been estimated.

“The controls are inherently similar people – elderly adults coming into hospital at the same time, with the same problem, but who did not have COVID-19,” said Adam Finn, professor of pediatrics at Bristol University, who is chief investigator for the study.

The Pfizer/Biontech vaccine was 71.4 % effective in preventing symptomatic illness severe enough to result in hospitalization; Astrazeneca’s vaccine was 80.4% effective. The median age of the Pfizer/Biontech vaccinated group was 87 and of the Astrazeneca group 88. All the patients had multiple co-morbidities.

“Despite frailty and age, one dose of [the] Pfizer/Biontech or Astrazeneca [vaccines] is remarkably effective at reducing hospitalization and serious disease,” said Catherine Hyams, clinical research fellow in respiratory disease, who is a co-author of the paper describing the study, which was published as a non-peer-reviewed preprint by The Lancet on March 3.

The data are important in demonstrating effectiveness in elderly, frail people who were not represented in phase III trials.

Finn, who is chair of the World Health Organization’s European expert technical advisory group on immunization, which advises on vaccination programs, said the findings are now of more relevance for countries in Europe which decided because of that shortage of data not to administer the Astrazeneca vaccine to their elderly populations, than they are for the U.K. Those include France, Italy, Spain and Germany.

“In the short term, the job is done in the U.K. The U.K is well forward, this age group is immunized and we’re now down to vaccinating [60 to 64]-year-olds,” said Finn. “But there are lots of doses of Astrazeneca vaccine available in European countries, and they are not being given to people over the age of 65; in some cases over the age of 55, for lack of data.

“Well here are the data. There are data from Public Health England and Public Health Scotland, and now from us, showing that you can save lives in elderly people by giving them a dose of vaccine,” Finn said.

In the U.K., rollout of the Pfizer/Biontech vaccine began on Dec. 8; Astrazeneca’s vaccine was in use from Jan. 4 onward. When the observations in the Bristol study were reconciled to cover the same period of 2021, the observed effectiveness of one dose of either vaccine is nearly identical, at 79.3% for Pfizer/Biontech’s and 80.4% for Astrazeneca’s.

Of 803 patients with acute respiratory disease who were 80 or older, 466 were eligible for the study. Of those, 144 (31%) tested positive for SARS-CoV-2.

Further vindication of U.K. strategy

The findings from Bristol match those reported recently from population level studies by Public Health Scotland (PHS) and Public Health England (PHE), but are based on a different study design. Rather than cross-referencing COVID-19 diagnostics results, immunization records and hospital admissions data, the Bristol research entailed a comprehensive, case-by-case examination of all patients admitted to the two hospitals.

That meant the date of onset of symptoms was known and it was possible to compensate for biases in the uptake of vaccines, and the different levels of transmission during the past three months.

“We essentially are finding similar results, but using a fundamentally different approach, so this increases confidence; their results [PHS and PHE] confirm ours; ours confirm theirs,” said Finn.

This is the first cut of data from the Pfizer-funded Bristol study, which will run for two years. Over time, more detail will be available on the length of protection from vaccination, whether people who are vaccinated but still need to be admitted to the hospital experience relatively less severe disease, and specific factors that make people less likely to be protected by vaccination.

In addition, the researchers expect to include estimates of effectiveness of vaccines against different circulating variants of SARS-CoV-2, as time goes on.

The findings are another vindication of the U.K. decision to maximize the public health benefits of limited COVID-19 vaccine supplies by giving as many first doses as possible. Rather than two doses at three weeks apart for Pfizer/Biontech, or two doses at four weeks apart for Astrazeneca, both vaccines are being administered 12 weeks apart.

“Spacing out doses turns out to have been the right thing,” Finn said. As a member of the independent group of experts advising the government on the vaccination strategy, Finn had a say in that decision, and in the strategy of starting vaccine rollout in the over 80s, who are most likely to experience severe disease and to be admitted to hospital if they are infected with SARS-CoV-2.

“Both of these vaccines are doing what we wanted them to do in the first place, which was to stop people coming into hospital and then dying,” said Finn.

That message is getting through: on March 2, French regulator Haute Autorité de santé reversed its position that Astrazeneca’s vaccine should only be administered to people under 65. Citing the PHS study and in the current context of 20,000 new cases per day, “vaccination of the most vulnerable is more than ever a central issue,” HAS said in a statement. “Faced with these encouraging results, HAS is redefining the role of the Astrazeneca vaccine in the vaccine strategy, by extending its use to people over 65 years of age.”