Covid-19 immunity may wane within months and so does vaccine efficacy, says study on long-term protection
Recovery from Covid-19 may not guarantee lifetime protection from the new coronavirus. A new study suggests that antibodies -- a type of protein produced by the immune system to fight intruders -- last only a few months, raising concerns over the efficacy of upcoming vaccines and the possibility of reinfection.
To understand the duration of immunity, researchers from King's College London studied 65 patients who tested positive for the virus, for 94 days. They also looked at 31 members of staff, who volunteered to have their antibody levels measured between March and June. The results showed that the proportion of two types of antibodies declined in 20-30 days. What is more, the body responded more strongly to a severe infection than a mild one.
Vaccines teach the body to generate antibodies with the hopes of offering long-term protection. "If your infection is giving you antibody levels that wane in two to three months, the vaccine will potentially do the same thing,” Dr Katie Doores, one of the authors of the study, told Guardian. “People may need boosting, and one-shot might not be sufficient.”
It is not surprising that antibodies against Covid-19 wane within months. Our bodies do not seem to generate potent and long-lasting antibodies against related human coronaviruses, thereby allowing reinfection. However, they only cause a common cold. As for the more serious ones such as SARS and MERS, antibodies remain in the blood for up to 12-14 months.
"Similar short-lived responses are seen against other human coronaviruses that predominantly cause only mild illness, meaning that we can be re-infected as time goes by and outbreaks can adopt seasonality," Stephen Griffins, associate professor in the University of Leeds School of Medicine, who was involved in the study said in a statement. If the new coronavirus follows the same pattern, it could spell trouble.
Other preliminary studies have also arrived at similar findings. A study by the Spanish government also found that antibody levels in recovered patients fell in a few weeks. It suggests that the immunity "can be incomplete, transitory and then disappear," Dr. Raquel Yotti, who lead the study, said in a news conference.
Researchers are urging young adults to stay cautious, adding that the current evidence suggests that herd immunity may not mean much.“I cannot underscore how important it is that the public understands that getting infected by this virus is not a good thing. Some of the public, especially the youth, have become somewhat cavalier about getting infected, thinking that they would contribute to herd immunity. Not only will they place themselves at risk, and others, by getting infected, and losing immunity, they may even put themselves at greater risk of more severe lung disease if they get infected again in the years to come," Prof Jonathan Heeney, from the University of Cambridge, told the Guardian.
Some experts have said that two other protective immune cells-- B and T cells -- may play some part in fighting off a second encounter with the virus. "So you might well get a milder infection," Dr Mala Maini, professor of viral immunology and consultant physician at the University College London, said. This is because these cells remember the first attack, preventing severe disease.
Doores of the King's College and the author of the study said that further studies should provide insights into the level of antibodies required to ward off infection. "We can draw some information from animal studies, but it is important to study individuals who have been previously infected with SARS-CoV-2 to see whether they become reinfected and if so, whether the severity of the disease is reduced," she said.
Dr Maria Van Kerkhove, head of the WHO’s emerging diseases unit, said questions on the strength and duration of antibodies remain. “So there are a number of studies underway that are trying to answer these questions,” she said at a press conference.
The research, which has not been tested for accuracy yet, is currently published in preprint format.