Quote (Saucisson6000 @ 23 May 2020 19:14)
What is "cross immunity"?
This expression is used to designate an immunity acquired during a first infection and which will protect later against another infectious agent (virus or bacteria). Generally, an antibody is specific. But sometimes, certain antibodies can fight against bacteria or viruses of similar species. Thus, individuals may have acquired protection against Sars-CoV-2 by having been exposed in the past to other coronaviruses causing common colds.
This hypothesis, which remains to be verified, was raised by American researchers in the specialized journal Cell. According to them, 40 to 60% of the population could be immunized against Covid-19 without even having been exposed to it. If this hypothesis is confirmed, Sars-CoV-2 would no longer have many people to infect.
I've read a hypothesis a couple of weeks ago, it was meant to explain why we saw so little difference between the outcomes of countries which went for a super strict lockdown and those which went for a soft one.
The idea was that the R_0 of Sars-CoV-2 is actually not in the ballpark of 2-3, it instead is about 5 or 6, but with around half the population not susceptible due to cross-immunities.