One dose of Pfizer or AstraZeneca vaccine was highly effective at preventing coronavirus in older people, real-world data from South Korea suggests

• One dose of Pfizer or AstraZeneca vaccines was more than 86% effective at preventing COVID-19, data shows.
• South Korean health officials said Tuesday that more than 520,000 Koreans over 60 had had a single shot.
• The data from South Korea didn't show how long protection lasts.

A single dose of Pfizer or AstraZeneca's COVID-19 vaccines was more than 86% effective at stopping coronavirus in older people at least two weeks after vaccination, real-world data from South Korea shows.

Both vaccines are authorized to be given as two injections, spaced weeks apart, but this data again shows that they offer some protection between doses.

The Korea Disease Control and Prevention Agency (KDCA) said on Twitter Tuesday that one dose of the vaccine co-developed by Pfizer and BioNTech was 89.7% effective at preventing COVID-19 in South Koreans aged over 60. The vaccine co-developed by AstraZeneca and Oxford University was 86% effective at preventing COVID-19 after one dose, it said.

The KDCA analysis included more than 520,000 people who had been vaccinated with a single dose of either vaccine.

In the data collected, 1,237 COVID-19 cases were reported, and only 29 came from the vaccinated group, the KDCA said in a press release.

The agency didn't provide a breakdown of how many people received each shot or the severity of illness - COVID-19 vaccines are generally more effective at preventing COVID-19 infections that cause hospitalization or death.

The KDCA said the vaccines' protective effect was higher when the second vaccination was completed, so a second shot within the recommended period was "absolutely necessary".

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South Korea's findings adds to a growing body of real-world data suggesting that a single shot of a COVID-19 vaccine protects against COVID-19, but it's still not clear how long protection from a single dose may last.

Real-world data from the UK, posted as a pre-print study on April 23, found that either Pfizer or AstraZeneca's vaccine cut COVID-19 infections with symptoms by 72%. Protection from a single dose probably holds up for at least 10 weeks, based on measurements of antibody levels, the study, which wasn't peer-reviewed, said.

Another real-world study from Scotland published in the Lancet on April 23 found that a single dose of Pfizer's vaccine was 91% effective against hospitalization at 28 to 34 days following vaccination. One dose of AstraZeneca's vaccine was 88% effective against hospital admissions after the same time period, the study found.