UK Edition
Millions of people who have already recovered from coronavirus are likely to have protection greater than that from the Oxford vaccine, raising questions about whether people should be antibody tested to avoid wasting jabs.
New research from Public Health England (PHE) shows antibodies from a previous infection provide at least 83 per cent protection from picking up the virus again – and possibly up to 99 per cent – for at least five months and probably much longer.
In contrast, the Oxford vaccine has a short-term efficacy of 73 per cent after one dose and longer-term protection of around 70 per cent after two doses.
In a sample of more than 6,600 healthcare staff who tested positive for an infection, just 44 people were reinfected within five months. Only two of those cases were deemed "probable", with the rest being classed as only "possible".
Professor Susan Hopkins, senior medical advisor at PHE said: "We now know that most of those who have had the virus, and developed antibodies, are protected from reinfection. Immunity gives you a similar effect to the Pfizer vaccine, and much better effect than the AstraZeneca, so that is reassuring for people.
"But there is still a risk that you could acquire an infection and transmit to others. Now more than ever it is vital we all stay at home to protect our health service and save lives."
In December, the Office of National Statistics (ONS) estimated that 4.4 million people had been infected in Britain since the start of the pandemic, while the MRC Biostatistics Unit at Cambridge University believes it could be as many as 8.9 million in England alone.
If the Cambridge data is correct, it means some 16 per cent of people in Britain have already been infected and are likely to have high levels of protection.
A recent study of health workers from PHE found that around one quarter already had some immunity to coronavirus, nearly half of whom had never been infected. It suggested some natural immunity may also be present in the population, possibly from other circulating coronaviruses such as the common cold.
The NHS is not checking whether people have been previously infected before vaccination, meaning large numbers may receive little extra benefit.
Currently, antibody testing everyone before vaccination would add an unhelpful level of complexity to an already logistically difficult rollout. However, experts believe it may be useful once the number of infected people reaches around one fifth of the population, which may not be too far away.
Sir John Bell, Regius professor of medicine at the University of Oxford, said: "The level of seropositivity has not been high enough to make it worthwhile doing a national antibody screen.
"You would need to do a lab Elisa [enzyme-linked immunosorbent assay] and we don't really have the data to show how much antibody is enough to protect. But if it were easy to get a very accurate result it would be worth it, particularly if the seropositive rate was 20 per cent, say."
Recent antibody research from the University of Milan showed the rate of previous infection rose with age, with around 32.9 per cent of over-60s showing antibodies to the virus, compared with just 8.2 per cent of under-20s. Although it was a small study from a village near Milan and has not been repeated in Britain, it may suggest that many people who are first in line for the vaccine are already protected from prior infection.
Yet experts say that giving a vaccine to those already protected may increase their protection further, in the same way as a booster shot, and could still be useful.
Professor Paul Morgan, the director of the Systems Immunity Research Institute at Cardiff University, said: "Even with prior infection-derived immunity, which may wane over months – and some antibody-positive individuals may have been infected nine months ago – the vaccine will provide a boost of immunity that can only have a positive effect overall."
And some scientists worry that antibody tests before vaccination would slow down the rollout to such a degree that it would erase any benefit. False positives could also mean those who need the vaccine would not receive a jab.
Paul Hunter, professor of medicine at the University of East Anglia, said: "It would be quite a lot of extra work and delay the process of getting the vaccine out. Also, we do not know how long natural immunity lasts – probably not forever, especially for people who have had a mild illness.
"So current advice is that even people who have had Covid need to have vaccine. Also, I am not sure how many false positives would be generated with rapid tests and so people who do need the vaccine are denied it."
However, the new results from PHE may reopen the door to immunity passports for people who have already had the virus, once a significant proportion of the population is vaccinated.
Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, said: "The study has major implications for how we can get out of the current crisis. The vast majority of the population will either need to have natural immunity or have been immunised for us to fully lift restrictions on our lives, unless we are prepared to see many more people being infected and dying from Covid-19."