A US study predicts that SARS-CoV-2 - the virus that causes COVID-19 - could eventually become no more infectious than the common cold, seasonally reappearing each year alongside other pathogens in the coronavirus family that bring about mild sniffles.
But that will happen only when the coronavirus becomes endemic, the point at which spread among human communities in a way that doesn't cause massive outbreaks or serious illness is the norm, according to the researchers from Emory University in Georgia and Penn State University.
Their study was published on Tuesday in the journal Science.
"The timing of how long it takes to get to this sort of endemic state depends on how quickly the disease is spreading and how quickly vaccination is rolled out," study lead author Jennie Lavine, a postdoctoral fellow at Emory University, told the New York Times.
"So really, the name of the game is getting everyone exposed for the first time to the vaccine as quickly as possible."
The team's model was based on studies on six human coronaviruses, four of which regularly spread among people and cause only mild symptoms.
The other two - severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) - emerged more recently and have higher fatality and infection rates but share similar genetics with the coronavirus that causes COVID-19.
Scientists are still learning how long antibodies and other immune cells against the coronavirus last after getting sick but evidence suggests that "infection-blocking immunity" disappears quickly, whereas "disease-reducing immunity is long-lived".
This means a person can be reinfected with the coronavirus some months after infection but their second, third or fourth time around wouldn't be as serious - similar to infections with the common cold.
The researchers say once the majority of people gain protection against COVID-19, either through natural infection or vaccination, most cases will occur "almost entirely in babies and young children," who are known to experience mostly mild illnesses.
Meanwhile, reinfections in older and more vulnerable individuals could still happen during the "endemic phase" but they could be protected from severe COVID-19 symptoms because of infections they experienced during childhood, according to the team's models.
Studies on common cold-causing viruses show these early illnesses occur mostly between age 3 and 5.
But without major vaccine rollouts, it can take many years of infections and deaths before the coronavirus becomes just another seasonal illness, the researchers said.
The COVID-19 vaccines are also not 100 per cent effective at preventing infection, so it's likely the jab will be better at preventing severe disease in the long run.
Reuters reported vaccine developers with Moderna said on Monday that immunity from their vaccine should last at least a year.
The team's predictions aren't promised, however, Dr Marc Lipsitch, an epidemiologist at the Harvard TH Chan School of Public Health in Boston, told the NYT.
"Their prediction of it becoming like common cold coronaviruses is where I'd put a lot of my money," Lipsitch told the outlet. "But I don't think it's absolutely guaranteed."
Even in the event new coronavirus strains reappear during the endemic phase, like the one from the UK that is now spreading in other countries, the researchers say immunity gained from previous strains "is nonetheless strong enough to prevent severe disease".
The same idea applies to reinfections with any of the four coronaviruses that cause the common cold, which appear to boost immunity with each sickness.
Australian Associated Press