In the best-case scenario, a vaccine and better treatments blunt COVID-19’s severity, making it a much less dangerous and less disruptive disease. Over time, SARS-CoV-2 becomes just another seasonal respiratory virus, like the four other coronaviruses that cause a sizable proportion of common colds: 229E, OC43, NL63, and HKU1. These cold coronaviruses are so common that we have likely all had them at some point, maybe even multiple times. They can cause serious outbreaks, especially in the elderly, but are usually mild enough to fly under the radar. One endgame is that SARS-CoV-2 becomes the fifth coronavirus that regularly circulates among humans.
In fact, virologists have wondered whether the common-cold coronaviruses also got their start as a pandemic, before settling in as routine viruses. In 2005, biologists in Belgium studied mutations in the cold coronavirus OC43, which likely evolved from a closely related coronavirus that infects cows. Because genetic mutations accumulate at a somewhat regular rate, the researchers were able to date the spillover from cows into humans to the late 1800s. Around this time, a highly infectious respiratory disease was killing cows, and even more curiously, in 1889, a human pandemic began killing people around the world. The older people were, the more susceptible they were. This illness, which produced “malaise, fever, and pronounced central nervous system symptoms,” was linked to influenza based on the antibodies found in survivors half a century later. But the cause was never definitively proved from tissue samples.
Could it have been a coronavirus that jumped from cows to humans? This is all speculative, and the possible links between the other three cold coronaviruses and past pandemics are even less clear, says Burtram Fielding, a coronavirus researcher at the University of the Western Cape. “But,” he says, “I wouldn’t be surprised.” It would also be good news, in a way, because it would suggest that COVID-19 could become less deadly over time, making that transition from pandemic to common cold.
With a virus, there is a general trade-off between how contagious it is and how deadly it is. SARS and SARS-CoV-2 are illustrative points of comparison: The earlier virus killed a much higher proportion of patients, but it also did not spread as easily. And what a virus ultimately wants to do is keep spreading, which is much easier to do from a live, walking host than a dead one. “In the grand scheme of things, you know, a dead host doesn’t help the virus,” says Vineet Menachery, a coronavirus researcher at the University of Texas Medical Branch. The other four coronaviruses may also be less deadly because we have all encountered them as children, and even if our immunity does not prevent us from getting them again, it may still prevent severe disease. All of this, along with immunity from vaccines, means that COVID-19 is likely to become far less disruptive down the line.