Immunity to Covid-19 may last only a few months, according to a U.K. study that casts doubts over the longevity of potential coronavirus vaccines.
Antibody responses to the coronavirus can peak three weeks after onset of symptoms, but then begin to decline after as little as two months, researchers at Kings College London found.
The study, published Saturday on preprint server MedRxiv and not yet peer-reviewed, examined the antibody levels of 64 patients and six health-care workers who had tested positive for the virus at Guy's and St Thomas' NHS foundation trust (which runs several London hospitals) between March and June. It also monitored 31 other members of staff who volunteered to have regular antibody tests.
Researchers found that levels of antibodies that can fight the coronavirus peaked three weeks after the onset of symptoms but then declined. While 60% of the people tested in the study had a "potent" level of antibodies after an average of 23 days following first onset of symptoms, only 16.7% had that level of antibodies 65 days after the first signs of symptoms.
The levels of antibodies were higher in patients who had more severe disease, although it is not clear why, the researchers said, and some individuals who developed antibodies were asymptomatic.
The researchers noted that their study found the antibody response to Covid-19 was similar to that of other human coronaviruses, such as SARS (severe acute respiratory syndrome) and seasonal coronaviruses associated with common colds, in which an individuals' antibody response tends to "wane over time, from as little as 12 weeks to 12-34 months after infection."
The study was led by Katie Doores from KCL's School of Immunology & Microbial Sciences. She said the study highlights that the antibody responses circulating in the blood are declining after infection and that further research is needed to determine the level of antibodies required for protection from infection.
"We need to continue to measure antibody responses in these individuals to see if antibody titres continue to drop or plateau to a steady state," she said. Antibody titres refer to the presence, and amount, of antibodies within a person's blood.
The research calls into question how much protection individuals who have had the coronavirus have from subsequent reinfection, and the durability of any potential vaccine.
World Health Organization officials said Monday that patients who recover from Covid-19 may be able to get the coronavirus again, citing similar studies that suggest immunity may wane after a few months.
Dr. Maria Van Kerkhove, head of the WHO's emerging diseases unit, said patients "do mount some level of an immune response."
Speaking at a news conference at the organization's Geneva headquarters, she added that, "what we don't know is how strong that protection is and for how long that protection will last."
"So there are a number of studies under way that are trying to answer these questions," she said.
A peer-reviewed study published in the Lancet medical journal last week claimed that Covid-19 antibodies in Spain's population were "insufficient to provide herd immunity," which refers to when a population is allowed some exposure to the virus in order to build immunity among the general population.