COVID-19 endemic stage two years away, Yale School of Medicine study suggests

To develop a better understanding of when and how COVID-19 might become endemic, researchers at Yale turned to rats, which, like humans, are also susceptible to coronaviruses.

The COVID-19 disease may reach endemic stage in the U.S. in at least two years, according to a modelling study conducted in rats.

The researchers noted that illnesses like the common cold and the flu have become endemic in human populations, meaning everyone gets them every now and then, but for most people, they aren't especially harmful.

To develop a better understanding of when and how COVID-19 might become endemic, researchers at the Yale School of Medicine in the U.S. turned to rats, which, like humans, are also susceptible to coronaviruses.

By collecting data on coronavirus reinfection rates among rats, they were able to model the potential trajectory of COVID-19.

Animals like pigs and chickens live with endemic coronaviruses, too, and a key factor identified in the spread of animal and human coronaviruses alike is their tendency to evoke what is known as non-sterilising immunity, they said.

"It means that initially there is fairly good immunity, but relatively quickly that wanes," said Caroline Zeiss, a professor at Yale School of Medicine and senior author of the study published in the journal PNAS on Tuesday.

"And so even if an animal or a person has been vaccinated or infected, they will likely become susceptible again," said Zeiss.