Health

Analysis: How close are we to COVID-19 herd immunity?

This week a clip of Dr Michael Ryan, from the World Health Organization, went viral when he provided a strong rebuke about hopes that herd immunity could help us to control the coronavirus.

“Humans are not herds,” he denounced, almost in anger. He went on to say: “I think we need to be really careful when we use terms in this way around natural infection 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.”

From the United Kingdom to Sweden, herd immunity has been much talked about and derided, as governments grapple with a coronavirus Dr Ryan also proclaimed “may never go away”.

Herd immunity is a concept in epidemiology that describes how people can collectively stave off infections if some percentage of the population has immunity to a disease. And, while we may not like the term, it is one of two ways to achieve high levels of immunity. The other is a vaccine and that still seems some way off.

But, if we are trying to find out if we are anywhere near herd immunity, there are two key questions for which we still dont have accurate answers. Just how much of the population has been infected? And if you have been infected, just how long do you have immunity for?

Though we are still unsure about the latter, we are starting to get initial data on how many people have already been infected and, frankly, its not good. Not good as in, its not that many people. And thats bad because it means the disease is as deadly as experts feared and we really are only at the start of the pandemic.

On Wednesday, a study of 60,000 people was published by the Spanish government. It suggested only five per cent of the country’s population has been infected, so far. The results did vary massively across the country: Madrid has a prevalence rate of 11.3 per cent; but in provinces in the south, east and north-west of the country, the rate is much lower. In Seville, for example, 2.3 per cent of people have contracted COVID-19.

Yesterday, a survey of 11,000 households in England suggested one in four hundred is currently infected with the virus – thats only 0.27 per cent of the population. And in France, a study led by the Pasteur Institute says 4.4 per cent of France (2.8 million people) has been infected. Researchers say the rate even in the worst-hit parts of the country – in the east part and in and around Paris – is still only between nine and ten per cent on average. These same researchers go on to explain that “around 65 per cent of the population should be immune if we want to control the pandemic by the sole means of immunity”.

Clearly, we are a long way from that, except for in Sweden where Johan Giesecke, an epidemiologist advising the authorities there, says Stockholm could reach herd immunity by June. Sweden, though, already has a death rate three times higher than that of its neighbour, Denmark, and seven times that of Finland.

The road back to normal remains a long one.

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