There remains an enormous amount we do not know about SARS-CoV-2. On the one hand we may be a very long way away from achieving “herd immunity” to SARS-CoV-2, the point at which enough people have resistance to the cease that its spread ceases or slows, as this piece at The Telegraph avers:
Dr Jefferson believes many viruses lie dormant throughout the globe and emerge when conditions are favourable, which also means they can vanish as quickly as they arrive.
“Where did Sars 1 go? It’s just disappeared,” he said. “So we have to think about these things. We need to start researching the ecology of the virus, understanding how it originates and mutates.
“I think the virus was already here – here meaning everywhere. We may be seeing a dormant virus that has been activated by environmental conditions.
“There was a case in the Falkland Islands in early February. Now where did that come from? There was a cruise ship that went from South Georgia to Buenos Aires, and the passengers were screened and then on day eight, when they started sailing towards the Weddell Sea, they got the first case. Was it in prepared food that was defrosted and activated?
“Strange things like this happened with Spanish Flu. In 1918, around 30 per cent of the population of Western Samoa died of Spanish Flu, and they hadn’t had any communication with the outside world.
“The explanation for this could only be that these agents don’t come or go anywhere. They are always here and something ignites them, maybe human density or environmental conditions, and this is what we should be looking for.”
I think that the genetic studies contradict that view but I present it in the interest of completeness. On the other hand herd immunity may be just around the corner as Allysia Finley declaims in the Wall Street Journal:
A small study last month from France found that six of eight close family contacts of sick patients didn’t develop antibodies but did develop Covid-19-specific T-cells. A new study from Sweden finds that moderately ill patients developed both Covid-19-specific antibodies and T-cells. But twice as many healthy individuals who donated blood during the pandemic and asymptomatic family members of sick patients generated Covid-19 specific T-cells than did antibodies.
“SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19,†the study concludes. “The observation that most individuals with asymptomatic or mild COVID-19 generated highly functional durable memory T cell responses,†not uncommonly in the absence of antibodies, “further suggested that natural exposure or infection could prevent recurrent episodes of severe COVID-19.â€
In short, antibody tests may significantly underestimate the number of people who have already been infected with Covid-19, especially if they had a milder strain. If so, it’s possible that some early hot spots, like New York City and northern Italy, already have a degree of herd immunity. The same may be true of other places soon.
There is some controversy about what percentage of the population must not be susceptible to the virus in order to achieve “herd immunity”—anything from 33% to 95% has been suggested. It would seem to me that graph theory would suggest that the actual percentage may depend very highly on circumstances.
“Schrödinger’s cat” was a thought experiment devised by the physicist Erwin Schrödinger. The scenario presents a hypothetical cat that may be simultaneously both alive and dead. Similarly, SARS-CoV-2 seems to be “Schrödinger’s virus”—simultaneously everywhere and nowhere.
My own view is that we should be making a drastically different set of assumptions than policymakers seem to be making, based on experience. “Spanish flu”, the flu that infected nearly a third of Americans in 1918 and killed millions worldwide, never vanished. It is still with us. It is now called A(H1N1) and broke out a decade ago as “swine flu” and people are still contracting it. It is a serious flu, more deadly than the seasonal flu, but we aren’t destroying our economy and society over it.
Let’s not assume that a vaccine will ever be produced for SARS-CoV-2 and that we never actually achieve “herd immunity”, whether because not enough people are susceptible to it or it evolves just fast enough to evade our immune systems. It seems to me that the appropriate measures for me, personally, to take given that assumption is to take the measures that seem prudent to avoid contracting the disease but otherwise just accept that life cannot be risk-free.
Under those circumstances what would be the most prudent public policies?