As Menachery sees it, the possibilities for the future when it comes to Covid-19 and human immunity break down as follows: sterilizing immunity, functional immunity, waning immunity, and lost immunity.
“So far, anyway, the evidence supports functional immunity, but the only way to see how long that will last is to follow people over time and see if those responses diminish,” she said.
“The idea there is that, yes, your antibodies might wane, but your memory responses aren’t absent,” said Menachery, noting that when a primed immune system re-encounters the virus, production of antibodies would kick into gear.
Christian Drosten, who is another co-discoverer of SARS-1, describes a future that fits into this category.
“I clearly expect lasting and relevant immunity that is almost sterilizing immunity against #SARS-2 in almost every person infected with SARS-2,” Drosten, director of the Institute of Virology at Berlin’s Charité University Hospital, said via email.
“It may be possible to become infected again, without any change in the virus. The resulting infection will be mild or asymptomatic, with significantly lower levels of virus replication and onward #transmission.”
Drosten’s last point would be a big bonus. If people who are reinfected don’t generate high levels of SARS-2 viruses in their respiratory tracts and therefore don’t contribute much to the spread of the virus, Covid-19 may become, over time, not just less dangerous, but also less common.
“It may become a rare infection, although that is difficult to foresee given the size of the global population,” Koopmans said.
Another hopeful part of this scenario relates to young children, who are far less likely than adults to develop severe disease. Krammer expects that children who first encounter the virus when they are very young may end up being infected several times over their lifetimes, but those later infections won’t lead to severe illness, even when they are elderly.