As the vaccine rollout continues combined with more people becoming infected the rate of those with Covid-19 antibodies, that provide resistance to the virus, increases.
The Office for National Statistics figures for adults in private households in the week to April 11 – 68.3 per cent – is up from an estimated one in two, or 53.1 per cent, recorded just two weeks earlier.
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The percentage of those with antibodies in England is higher than the rest of the UK.
In Wales, an estimated six in 10 adults in private households would have tested positive for Covid-19 antibodies in the week to April 11, the ONS said. This is up from around one in two adults two weeks earlier.
The latest estimate for Scotland is six in 10 adults, up from just over four in 10, while for Northern Ireland the estimate is also six in 10 adults, up from just over one in two.
Prof Openshaw, a member of the Covid-19 clinical information network, described the results as “very, very reassuring and “certainly better than many of us expected just a few months ago”.
He told the BBC Radio Four Today programme: “It shows that the immune system is doing something a lot more than we were expecting of it really.”
He said it is known from other studies that infection is “typically much milder” in people who have been vaccinated and added that with two doses the outcome is “almost certainly going to be even better”.
It was also revealed that one in four people get mild side effects from the vaccine – including headaches and fatigue.