UK may have sufficient herd immunity to COVID-19, says Oxford University study

The UK population may already have developed sufficient levels of herd immunity required to prevent a feared second wave of the coronavirus pandemic in the country, notes an Oxford University study involving professor Sunetra Gupta.

In a paper titled The impact of host resistance on cumulative mortality and the threshold of herd immunity for SARS-CoV-2, Gupta along with three other Oxford University colleagues notes that the herd immunity threshold (HIT) required to prevent a resurgence of the deadly coronavirus may have already been built up due to exposure to seasonal coronaviruses, such as the common cold.

“It is widely believed that the herd immunity threshold (HIT) required to prevent a resurgence of SARS-CoV-2 (COVID-19) is in excess of 50 per cent for any epidemiological setting.

"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 cross-protection from exposure to seasonal coronaviruses,” notes the paper.

“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,” it says.

The new theory, which is yet to be peer-reviewed and analysed, suggests that when resistant people mix with non-resistant people, the herd immunity "threshold" drops sharply.

Gupta, a professor of theoretical epidemiology at Oxford University, has previously called on a focus on increased antibody testing to determine the levels of immunity already being built up in the UK population against the deadly virus.

"Given the mounting evidence that exposure to seasonal coronaviruses offers protection against clinical symptoms, it would be reasonable to assume that exposure to SARS-CoV-2 itself would confer a significant degree of clinical immunity," she and her colleagues, Jose Lourenco, Francesco Pinotti and Craig Thompson, note in their study.

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

For diseases where a vaccine is available, herd immunity is often calculated with the assumption that everybody has the same level of immunity – known as a homogenous model.

But a number of studies into the novel coronavirus, which has claimed over 45,000 lives in the UK, have been focussed on the differing levels of immunity within the population given the lack of a vaccine yet.