Officials of the World Health Organization (WHO) have cautioned that recent data show that though rare, individuals who were once infected with coronavirus could be infected again as their antibody reaction declines.
“We have seen the number of people infected continue to grow, but we’re also seeing data emerge that protection may not be lifelong, and therefore we may see reinfections begin to occur,” Dr. Mike Ryan, executive director of the WHO’s health emergencies program, said during a press briefing at the organization’s Geneva headquarters. “So the question is: What are the levels of protection in society?”
According to the US Centers for Disease Control and Prevention, reinfection is a scenario when a person who is infected with the virus, recovers and then later becomes infected again. COVID-19 reinfections are expected based on the CDC’s experience with other viruses, said WHO.
However, among other factors, researchers are trying to assess how likely and how frequently reinfection occurs, such as how severe reinfection may be and how soon it may occur after the first infection.
Researchers are also trying to decide how long an antibody response lasts after someone is infected with the virus, said Maria Van Kerkhove, head of the WHO’s emerging diseases and zoonosis unit.
“What we understand is 90 percent to 100 percent of people who are infected with the coronavirus do develop an antibody response, whether you have mild infection, asymptomatic infection, all the way to severe infection,” she said.
Ongoing research indicates an immune response may last for six months or longer, she said. In a recent Oxford study, researchers found that people who have contracted the coronavirus are “highly unlikely” to contract the disease again for at least six months.
The study, conducted between April and November with 12,180 health-care workers employed at Oxford University Hospitals, found that 89 of 11,052 staff without antibodies developed a new infection with symptoms. None of the 1,246 staff with antibodies developed a symptomatic infection.
“In some people, it may wane after a few months, but we do get a good indication that natural infection immune response is lasting for some months,” Ms. Van Kerkhove said. “We’re about a year into this pandemic, and so we still have a lot to learn.”
In late August, researchers in Hong Kong reported what appeared to be the first confirmed case of COVID-19 reinfection after a 33-year-old man who was first infected with the virus in late March appeared to contract the virus again more than four months later. The WHO acknowledged at the time that, though rare, reinfection could be possible.
“It doesn’t mean that it’s happening a lot; we know that it’s possible,” Ms. Van Kerkhove said.