Is Coronavirus Burning Out After 20% of a Population Is Infected?
The article points out that the virus seems to be burning itself out once it infects 20% of a given population. From cruise ships to hard hit cities that figure seems to keep coming up. If true, it is certainly better than expected. It also means the lockdowns may soon be over.
Read the rest of the article at the link.More than half a million people have died from COVID-19 globally. It is a major tragedy, but perhaps not on the scale some initially feared. And there are finally signs that the pandemic is shuddering in places, as if its engine is running out of fuel. This has encouraged many governments to relinquish lockdowns and allow everyday life to restart, albeit gingerly.
The spread of SARS-CoV-2 has been difficult to predict and understand. On the Diamond Princess cruise ship, for example, where the virus is likely to have spread relatively freely through the air-conditioning system linking cabins, only 20% of passengers and crew were infected. Data from military ships and cities such as Stockholm, New York and London also suggest that infections have been around 20% – much lower than earlier mathematical models suggested.
This has led to speculation about whether a population can achieve some sort of immunity to the virus with as little as 20% infected – a proportion well below the widely accepted herd immunity threshold (60-70%).
The Swedish public health authority announced in late April that the capital city, Stockholm, was “showing signs of herd immunity” – estimating that about half its population had been infected. The authority had to backtrack two weeks later, however, when the results of their own antibody study revealed just 7.3% had been infected. But the number of deaths and infections in Stockholm is falling rather than increasing – despite the fact that Sweden hasn’t enforced a lockdown.
Hopes that the COVID-19 pandemic may end sooner than initially feared have been fuelled by speculation about “immunological dark matter”, a type of pre-existing immunity that can’t be detected with SARS-CoV-2 antibody tests.
Antibodies are produced by the body’s B-cells in response to a specific virus. Dark matter, however, involves a feature of the innate immune system termed “T-cell mediated immunity”. T-cells are produced by the thymus and when they encounter the molecules that combat viruses, known as antigens, they become programmed to fight the same or similar viruses in the future.
Studies show that people infected with SARS-CoV-2 indeed have T-cells that are programmed to fight this virus. Surprisingly, people never infected also harbour protective T-cells, probably because they have been exposed to other coronaviruses. This may lead to some level of protection against the virus – potentially explaining why some outbreaks seem to burn out well below the anticipated herd immunity threshold.