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Herd immunity may be closer than thought

The idea that more people may have immunity to coronavirus than show up in standard antibody surveys is getting more oxygen by the day. It is what may explain why the epidemic often goes into decline when 10-20% of the population has antibodies, why the epidemic is now considered over in Sweden and why countries that are lifting restrictions are seeing no second waves, only the occasional ripple.

This week the British Medical Journal added its voice to those arguing that population immunity may be closer than was originally thought. The Times reports:

Tests for antibodies may be dramatically underestimating the proportion of people who have been infected with the coronavirus, scientists said.

The claim, made in the BMJ, implies that it is possible some parts of the country are far closer to herd immunity than had been thought.

The original misdiagnosis, the authors explain, is because we’ve been testing not for the full range of human immune responses but for just one or two types of antibodies.

Dr [Stephen] Burgess [from the Medical Research Council Biostatistics Unit at Cambridge University] said that calibrating tests using people who had been more severely ill may mean that a lot of asymptomatic infections are being missed.

“This might explain why, in cities such as London, we have seen the breakdown of widespread social distancing but infection rates have still not increased sharply,” he said.

Public Health England estimated London’s antibody prevalence at the start of May to be around 17.5%, not far from New York City’s 20%. Neither city has seen a rise in hospital admissions or deaths as restrictions have eased.

Eleanor Riley, professor of immunology at Edinburgh University, has some wise words on the subject which our politicians ought to heed:

“We need to think of the seroprevalence data as indicating that at least that proportion of people have been infected and it is likely higher. How much higher is difficult to estimate,” she said.

She added that it was important to consider who was susceptible to being ill as well as who was susceptible to infection: “We are learning that many people have pre-existing immunity which is likely due to prior infection with other coronaviruses.”

Dr Burgess said that he did not understand why more scientists were not questioning the seroprevalence data, as the extent to which it undercounts is critical.

“We’ve been asking ourselves the question of why this has not got more attention. It is clearly very important to our understanding of the disease,” he said.

“I think scientists are cautious, and would prefer to say nothing if they are not sure, even when saying nothing also has consequences.”

Unfortunately, not all scientists are so timid with their views. Could it be the silence of too many sceptical scientists that has allowed more confident scientists like Neil Ferguson to become so influential? As Dr Burgess notes, saying nothing also has consequences.

The BMJ deserves credit for publishing this paper, particularly as herd immunity is still being treated by some as politically toxic.

Source: Lockdown Sceptics