An interesting read.
>>The faded nightmares of our past — pandemics that terrorized, then receded, such as SARS in 2003 and flu in 1918-20 and again in 1957, 1968 and 2009 — went away not because the viruses evolved to cause milder disease, but for other reasons. In the case of SARS, the virus made people sick enough that health workers were able to contain the disease before it got out of hand. “People who got SARS got very sick, very fast and were easily identified, easily tracked and readily quarantined — and their contacts were also readily identified and quarantined,” says Mark Cameron, an immunologist at Case Western Reserve University in Cleveland, who worked in a Toronto hospital during the height of the SARS outbreak there. That was never going to be as easy to do for Covid-19 because people who don’t show symptoms can spread the virus.
Flu pandemics, meanwhile, have tended to recede for another reason, one that offers more hope in our present moment: Enough of the population eventually becomes immune to slow the virus down. The H1N1 influenza virus that caused the 1918 pandemic continued as the main influenza virus until the 1950s, and its descendants still circulate in the human population. What made the virus such a threat in 1918-20 is that it was novel and people had little immunity. Once much of the population had been exposed to the virus and had developed immunity, the pandemic waned, although the virus persisted at a lower level of infections — as it does to this day. It appears less lethal now largely because older people, who are at greatest risk of dying from influenza, have usually encountered H1N1 influenza or something like it at some point in their lives and retain some degree of immunity, Read says.
With the new coronavirus, Parrish says, “we’re sort of in that 1918 period where the virus is spreading fast in a naive population.” But that will change as more people either catch Covid-19 or are vaccinated (if and when that becomes possible) and develop some level of immunity. “There’s no question that once the population is largely immune, the virus will die down,” Parrish says.
The question is how long that immunity will last: for a lifetime, like smallpox, or just a few years, like flu? In part, that will depend on whether the vaccine induces a permanent antibody response or just a temporary one. But it also depends on whether the virus can change to evade the antibodies generated by the vaccine. Although coronaviruses don’t accumulate mutations as fast as flu viruses, they do still change. And at least one, which causes bronchitis in chickens, has evolved new variants that aren’t covered by previous vaccines. But at this point, no one knows what to expect from SARS-CoV-2.<<
https://www.smithsonianmag.com/science-nature/how-viruses-evolve-180975343/