Once most adults are immune to the novel coronavirus, whether by natural infection or inoculation, it's likely that the virus—a "grim menace now"—will be "no more of a threat than the common cold," according to a new study published in Science, Apoorva Mandavilli writes for the New York Times.

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Study details

For the study, Jennie Lavine, a postdoctoral fellow at Emory University, and colleagues, hypothesized when and how the novel coronavirus might become "endemic"—which is to say, a pathogen in low-level circulation that rarely results in severe illness—by assessing six other human coronaviruses.

Those coronaviruses included the four that cause the common cold, which are considered endemic, and the SARS and MERS viruses, which during their 2003 and 2012 outbreaks, respectively, caused severe illness but did not circulate widely. According to Lavine's study, all six of these coronaviruses spur similar immune responses, but the novel coronavirus appears most similar to the four that cause the common cold.

Based on that hypothesis, Lavine and her colleagues reassessed data from an earlier study that found people's first infection with the common cold viruses tends to happen between the ages of 3 and 5. That's a time when people's bodies are frequently encountering new-to-them pathogens, Mandavilli writes.

Then, as people get older, they repeatedly become infected with the common cold, but they typically do not get severely ill, in part because the repeat infections bolster immunity and keep the viruses in circulation. And that's the future the researchers ultimately anticipate for the novel coronavirus, once most adults develop immunity, Mandavilli writes.

That said, the timeframe for the novel coronavirus' transition to an endemic virus varies widely depending on how and when adults become immune. For instance, if we relied on natural infections alone, the transition could take anywhere from several years to several decades, depending on how quickly the virus spreads and on the strength and durability of people's immune response. And the price for immunity in this fashion, without a vaccine, would be steep, with "widespread illness and death along the way," Mandavilli writes.

But according to the study, a quick vaccination rollout could cut that timeline down to six months or a year.

Comments

According to Mandavilli, other experts agreed with Lavine's hypothesis.

"The overall intellectual construct of the paper I fully agree with," Shane Crotty, a virologist at the La Jolla Institute for Immunology, said. If on the one hand, the vaccines halt the coronavirus' transmission, "then it becomes a lot more like the measles scenario, where you vaccinate everybody, including kids, and you really don't see the virus infecting people anymore," he explained. But it's more plausible that the vaccines will protect people only from illness, not infection or transmission—meaning the coronavirus will remain in circulation.

Jennifer Gommerman, an immunologist at the University of Toronto, added, "It's unlikely that the vaccines we have right now are going to provide sterilizing immunity," the sort needed to prevent infection. That's because they don't currently provide the strong immune response in the nose and throat that's caused by a natural infection, she explained—which increases the odds infections will continue to happen, even after inoculation.

On the other hand, Marc Lipsitch, an epidemiologist at the Harvard T.H. Chan School of Public Health, warned that Lavine's hypothesis depends on the assumption that the novel coronavirus is like the coronaviruses that cause the common cold, an assumption that he says may not hold up. "Other coronavirus infections may or may not be applicable, because we haven't seen what those coronaviruses can do to an older … person" who hasn't yet been exposed to the virus, he said.

Lipsitch added that the novel coronavirus may instead turn out similarly to the seasonal flu, which over the years can be mild or severe by turn—and the various new variants of the novel coronavirus, particularly those that make it more difficult to provoke an immune response, might further complicate the issue. "Their prediction of its becoming like common cold coronaviruses is where I'd put a lot of my money," Lipsitch said. "But I don't think it's absolutely guaranteed" (Mandavilli, New York Times, 1/12).