Britain may have reached ‘herd immunity’

‘The threshold may be greatly reduced if a fraction of the population is unable to transmit the virus’

Bill Gardner

THE UK may have already achieved a sufficient level of herd immunity to prevent a second wave of Covid-19, an Oxford University study has suggested.

Scientists believe the “threshold” of herd immunity may have been lowered because many people may already be immune to the disease without ever having caught it.

According to a model produced by the Oxford team, as few as 20 per cent of the population may need to be resistant to the virus in order to prevent a new epidemic spreading.

“It is widely believed that the herd immunity threshold (HIT) required to prevent a resurgence of Sars-cov-2 is in excess of 50 per cent for any epidemiological setting,” the study says.

“Here, we demonstrate that HIT may be greatly reduced if a fraction of the population is unable to transmit the virus due to innate resistance or crossprotection from exposure to seasonal coronaviruses.

“These results help to explain the large degree of regional variation observed in seroprevalence and cumulative deaths and suggest that sufficient herd immunity may already be in place to substantially mitigate a potential second wave.”

Experts have suggested that a sizeable number of people may have immunity because of Covid-19’s similarity to viruses including the common cold.

The Oxford model, which has not yet been peer-reviewed, suggests that when resistant people mix with nonresistant people, the herd immunity “threshold” drops sharply.

“Given the mounting evidence that exposure to seasonal coronaviruses offers protection against clinical symptoms, it would be reasonable to assume that exposure to Sarscov-2 itself would confer a significant degree of clinical immunity,” the study says.

“Thus, a second peak may result in far fewer deaths, particularly among those with comorbidities in the younger age classes.”

Last month, Sir John Bell, Regius Professor of Medicine at Oxford University, who is working with a team at Oxford to develop a vaccine, said there was likely to be a “background level” of protection for a “significant number of people”.