- Countries hit hard by the coronavirus, like Spain, France, and the US, are finding that even devastating waves of coronavirus infections haven’t gotten their populations anywhere near the threshold of herd immunity.
- An estimated 5% of these countries’ populations have coronavirus antibodies – a far cry from the 50-70% required to stop the virus’s spread.
- Experts warn against a “very brutal arithmetic” that sacrifices lives for the goal of herd immunity.
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As more coronavirus antibody tests roll out across the globe, it’s becoming increasingly clear that no place is anywhere near the distant, bright horizon of “herd immunity.”
Populations achieve that benchmark when enough people become infected and recover – thereby developing pathogen-fighting antibodies – to prevent the virus from spreading. For COVID-19, experts estimate the threshold for herd immunity may be as high as 70% of the population.
So far, the first wave of infections has left more than 300,000 people dead worldwide and devastated the global economy. But even the hardest-hit countries are finding that scarcely 10% of their populations have walked away with antibodies.
Tens of thousands are dead, but only 5% of the population may be immune
This week, studies in Spain and France suggested that no more than 5% of those populations have developed COVID-19 antibodies. Each country has reported more than 27,000 deaths from the virus as of Thursday.
Spain’s evidence shows that “large outbreaks and excess mortality do NOT produce meaningful herd immunity,” William Hanage, an epidemiologist at Harvard, said on Twitter.
In the US, where nearly 85,000 people have died, the prospects for mass immunity are no better. In April, a study in Santa Clara County, California, estimated that between 2.5% and 4.2% of residents there had antibodies. A study of Los Angeles County made a similar estimate: 2.8% to 5.6% “seroprevalence” (the term for the percentage of people who have antibodies in their blood).
A New York antibody study found that 13.9% of New York state residents had been infected with the coronavirus. In New York City, seroprevalence was as high 21.2% – but that was among people who sought out tests (meaning they might have thought they had symptoms). That’s still a far cry from the 50-70% required for herd immunity.
That doesn’t bode well for other parts of the US, which haven’t yet faced devastating waves of infections like the one that killed more than 27,500 people in New York.
“In the US, I estimate there is no more than ~5% seroprevalence,” Natalie Dean, a biostatistician at University of Florida, wrote on Twitter. “I don’t see any realistic way to reach any [herd immunity] threshold without many, many more deaths.”
‘Humans are not herds’
Even Sweden, which has largely allowed life to continue as normal since the beginning of the pandemic, seems nowhere near herd immunity.
Sweden’s own public health agency has estimated that, at best, about a quarter of the population of Stockholm might have contracted COVID-19. Over 3,500 people have died in the country – more than 12% of its confirmed cases.
“This idea that, ‘well, maybe countries who had lax measures and haven’t done anything will all of a sudden magically reach some herd immunity, and so what if we lose a few old people along the way?’ This is a really dangerous, dangerous calculation,” Mike Ryan, executive director of health emergencies at the World Health Organisation, said on a call with reporters on Monday.
“Humans are not herds,” Ryan added. “I think we need to be really careful when we use terms in this way around natural infections in humans, because it can lead to a very brutal arithmetic which does not put people and life and suffering at the centre of that equation.”
Vaccines are the best way to build herd immunity
Eventually, communities or countries could achieve herd immunity through vaccination. But experts say the world should plan to get through the next two years of COVID-19 without it.
Until a vaccine becomes widely available, experts recommend closely monitoring the virus through widespread testing and contact tracing, then isolating infected people and anyone with whom they came into contact. Governments may also need to re-close businesses and put restrictions back into place if infections threaten to surpass local hospital capacities again.
“A very low proportion of the people that have been tested have evidence of antibodies,” Maria Van Kerkhove, a WHO epidemiologist, said at a press conference on Monday. “We have a long way to go with this virus, because the virus has more people that can be infected.”
Hilary Brueck contributed reporting.
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