Herd immunity to COVID-19 might be impossible

A new study suggests immunity to COVID-19 may last less than three months, meaning the virus could reinfect people repeatedly.

The paper, from researchers at King’s College in London, has not yet been subjected to peer review, but if confirmed, would mean that ‘herd immunity’ might be a pipe dream.

It suggests that antibody responses to the virus may decline after as little as 20 days. Antibodies are proteins produced by the body to fight infections.

Despite the global search for a vaccine, no health authority has been able to establish whether people who contract COVID-19 can be infected by the disease again.

“This work confirms that protective antibody responses in those infected with SARS-COV2, the coronavirus that causes COVID-19, appear to wane rapidly. While longer lasting in those with more severe disease, this is still only a matter of months,” Stephen Griffin, associate professor at the University of Leeds School of Medicine, told CNN.

“Similar short-lived responses are seen against other human coronaviruses that predominantly cause only mild illness, meaning that we can be reinfected as time goes by and outbreaks can adopt seasonality. With the more serious, sometimes fatal, outcomes of SARS-COV2, this is troubling indeed,” Prof. Griffin said. “Vaccines in development will either need to generate stronger and longer-lasting protection compared to natural infection, or they may need to be given regularly.”

MIT Technology Review said if COVID-19 can reinfect people repeatedly, herd immunity may never arrive, “either through a one-shot vaccine or through community spread of the virus, as any protective antibodies would wane with time”.

However, it pointed out T cells that can destroy the virus can also offer some protection, and there have not yet been any confirmed cases of people catching COVID-19 a second time.

T cells are white blood cells that play a key role in the immune system. “Their roles include directly killing infected host cells, activating other immune cells … and regulating the immune response.”

Another expert believes even if we have no antibodies, B and T cells “can rapidly kick into action to start up a new immune response if you re-encounter the virus”.

“So you might well get a milder infection,” said Dr Mala Maini, professor of viral immunology at the University College, London.

“But this study does reinforce the message that we can’t assume someone who has had COVID-19 can’t get it again just because they initially became antibody positive,” said Dr Maini.

“It also means a negative antibody test now can’t exclude you having had COVID-19 a few months ago. And it suggests vaccines will need to be better at inducing high levels of longer-lasting antibodies than the natural infection or that doses may need to be repeated to maintain immunity.”

A Chinese study, released in June and published in the online journal Nature Medicine,found that eight weeks after recovery from the disease, antibody levels in study subjects fell to undetectable levels in 40 per cent of asymptomatic people and 13 per cent of symptomatic people, medscape.com reported.

“Together, these data might indicate the risks of using COVID-19 ‘immunity passports’ and support the prolongation of public health interventions, including social distancing, hygiene, isolation of high-risk groups and widespread testing,” the authors wrote.

A Spanish study involving 61,000 people, the largest in Europe, also concluded that COVID-19 antibodies can disappear within weeks.

Dr Raquel Yotti, head of the Carlos III Health Institute, said any perceived immunity “can be incomplete, transitory and then disappear”.

How long do you think it will be before we have a medical solution to COVID-19? Do you believe we will find one?

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Written by Will Brodie

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