A study by the British government shows both the Pfizer and AstraZeneca vaccines are more than 80 percent effective in preventing hospitalization from the coronavirus for people aged over 80.
Public Health England released the data including the rate of hospitalizations and deaths in confirmed COVID-19 cases.
The data suggest a single dose of either vaccine is more than 80 percent effective at preventing hospitalization, around three to four weeks after receiving the shot.
The health authorities also say there's evidence for an 83 percent reduction in coronavirus deaths with the Pfizer vaccine.
The death reduction ratio for the AstraZeneca vaccine is not known yet. The health authorities say that there was not enough data as the vaccine was rolled out later than the Pfizer one.
Britain began administering the vaccine developed by Pfizer and BioNTech last December, and started using the vaccine from AstraZeneca and the University of Oxford in January.
In people aged 70 years and older, the data shows that a single dose of the Pfizer vaccine was between 57 and 61 percent effective in reducing COVID-19 infections four weeks after the first shot. On the other hand, the ratio for the AstraZeneca vaccine was between 60 and 73 percent.
But a senior British health official told the news conference that a second dose is necessary to increase the vaccine's efficacy and lasting immunity.
Another official at the Public Health England also said more work needs to be done to understand the impact of the two vaccines in reducing infections.