It is possible that a significant number of people who’ve never been infected with the novel coronavirus already possess some immunity to it.
In last week’s roundup, we featured a study that found that a survivor of SARS possessed an antibody that ostensibly confers immunity to COVID-19. This was auspicious for our odds of developing an effective novel-coronavirus vaccine since an antibody capable of neutralizing viruses as distinct as SARS and the COVID-19 bug should be versatile enough to neutralize all mutated versions of the latter.
This said, even if every SARS survivor were immune to the novel coronavirus, it would make little immediate difference epidemiologically, as only an infinitesimal fraction of humans were ever infected with SARS.
But SARS and MERS weren’t the only forerunners of our present affliction. Several common colds are also coronaviruses. And if a significant percentage of people who’ve recovered from such colds possess cross-reactive immunity to SARS-CoV-2, then the population liable to contract COVID-19 — and spread the novel coronavirus — would be smaller than previously feared.
A recent study from the Center for Infectious Disease and Vaccine Research and the La Jolla Institute for Immunology suggests that this might be the case. Examining blood samples taken between 2015 and 2018 (when the novel coronavirus was still just a twinkle in Satan’s eye), researchers found that roughly 50 percent of these blood-givers possessed “SARS-CoV-2-reactive CD4+ T cells” — which is to say, their immune systems appeared capable of immediately recognizing and combating the novel coronavirus. Since none of these individuals could have been exposed to SARS-CoV-2, the most likely explanation for their possession of such T cells is previous exposure to a common-cold coronavirus.
Now, this was just a single study of blood samples. It remains unclear how prevalent these T cells actually are in the general population and how effective they truly are in combating COVID-19. But it’s at least possible that SARS-CoV-2 will suffer a fate not entirely dissimilar to the 2009 H1N1 swine flu, whose spread was undermined by the “immunological head start” humanity had derived from similar influenza strains.
https://nymag.com/intelligencer/2020/05/coronavirus-studies-updates-good-news-bad-news-herd-immunity.html