A single dose of the Pfizer coronavirus vaccine is “highly protective” after three weeks, according to a new study.
Researchers at the University of East Anglia (UEA) said the vaccine developed by Pfizer and BioNTech was still effective after 21 days without a “top up” dose in the recommended time frame.
It comes after a study by the University of Oxford found its coronavirus vaccine with AstraZeneca offers protection of 76 per cent up to 12 weeks after a single dose and may reduce transmission by 67 per cent.
The UEA study, which has not yet been peer reviewed, looked at data from Israel where the vaccine has been rolled out.
Scientists found the vaccine becomes 90 per cent effective after 21 days – supporting UK plans to delay the timing of a second jab.
While it is not yet known how long immunity lasted beyond 21 days without a second dose, researchers believe it is “unlikely” to majorly decline during the following nine weeks.
But scientists warned people’s risk of infection doubled in the first eight days after the Pfizer vaccine jab, citing people becoming less cautious as a possible cause.
Lead researcher Professor Paul Hunter, from UEA’s Norwich Medical School, said: “A recent non-peer-reviewed pre-print paper based on Israel’s experience looked at data from 500,000 people who had been given the Pfizer vaccine. It reported that a single dose may not provide adequate protection.
“But we saw a number of flaws in how they looked at the data including the fact that they did not attempt to estimate the effectiveness of the vaccine from day 18 onwards.
“This would have given a better indication of how effective a single dose of the vaccine could be if the second dose was delayed by up to 12 weeks.”
Researchers analysed data to see the impact of the Israeli vaccination programme on case numbers, and went on to estimate vaccine effectiveness over time.
They found that after the initial vaccination case numbers increased for eight days before declining “to low levels” by day 21.