Studies of previous coronavirus outbreaks shed some light on immunity to COVID-19, but data is incomplete.
We’d like to think that a bout with COVID-19 would yield lifetime immunity to the deadly virus, but an April 13 article in The New York Times doesn’t give any such assurances.
So far, writes Marc Lipsitch a professor at the Harvard T.H. Chan School of Public Health, “only the first glimmers of data are available about immunity to SARS-CoV-2, the coronavirus that causes Covid-19.”
SARS-CoV-2 is the third major coronavirus epidemic to affect humans in recent times, writes Lipsitch. The other two included the SARS outbreak of 2002-2003 and the MERS outbreak that started in 2012. Immunity data from those outbreaks suggest that being infected with COVID-19 could provide “some protection over the medium term—at least a year.” Then, the effectiveness of the immune response might decline.
If these trends hold, we could experience the buildup of “herd immunity” around the world as more and more people become immune to the virus, causing the number of cases to decline and hopefully leading to its containment. But it’s hard to put total confidence in that scenario because limited testing has yielded limited data about COVID-19 infection rates.
“For now, it is reasonable to assume that only a minority of the world’s population is immune to SARS-CoV-2, even in hard-hit areas,” writes Lipsitch. “How could this tentative picture evolve as better data come in? Early hints suggest that it could change in either direction.”
Getting a handle on immunity—and doing it quickly—is extremely important for those tasked with figuring out whether some people can re-enter society safely, writes Lipsitch.
But a host of unanswered questions cloud the immunity picture. For example, will some people find themselves at greater or lesser risk of infection with SARS-CoV-2 because of a prior history of exposure to coronaviruses? Can immunity to a coronavirus exacerbate an infection rather than prevent or mitigate it?
“More science on almost every aspect of this new virus is needed, but in this pandemic, as with previous ones, decisions with great consequences must be made before definitive data are in,” concludes Lipsitch.