“Recent studies have also found that many people with mild or no symptoms who test positive for Covid-19 later don’t show antibodies when tested. Patients with mild symptoms produce a weaker antibody response than those who get more severely ill. Most antibody tests are primed to minimize false positives, but as a result are less sensitive.
These people, however, have been found to have long-lasting, potent T-cells that can ward off future infection. 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.”
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.”
https://www.wsj.com/articles/herd-immunity-may-be-closer-than-you-think-11594076237?fbclid=IwAR1UNQ0jK5GWI-MLw9xwZFOE6Gtdv_lr0eh05iNKXMN8Un62TojX-v6xbL8
