Antibody levels fell by half every 73 days, says survey
People recovering from coronavirus infections start to lose immunity within a few weeks after they have been infected, especially if they have mild symptoms or no symptoms.
A study in the New England Journal of Medicine calls for caution regarding so-called herd immunity as well as the durability of vaccines.
A team at the University of California, Los Angeles, did an in-depth study of 34 people who had recovered from mild coronavirus infections and tested their blood two or three times over three months and found a rapid drop in antibodies — the immune system proteins that help stop viruses from infecting cells in the body. On average, the antibody levels fell by half every 73 days, F Javier Ibarrondo and Dr Otto Yang of UCLA’s David Geffen School of Medicine and colleagues reported in The New England Journal of Medicine.
According to the report, just two persons needed supplemental oxygen and received an HIV medication, and none were on a ventilator or getting Gilead Sciences Inc’s remdesivir. The first analysis was done on antibodies taken an average of 37 days after symptoms began, with a second after about 86 days, or less than three months. The researchers found that antibody levels fell quickly, with a half-life of about 73 days between the two-time frames. The loss of antibodies occurred more quickly than with SARS, an earlier type of coronavirus infection.
The antibody response is being closely studied by scientists worldwide for indications of how long-lasting immunity may be.
While there’s little evidence to suggest reinfections are broadly occurring, health experts have yet to pin down specifics. The latest findings raise concern that protection from reinfection may not last long in those with mild symptoms, which accounts for the majority of cases.
Further studies will be needed “to define a quantitative protection threshold and rate of decline of antiviral antibodies beyond 90 days,” according to the researchers led by F Javier Ibarrondo, from the David Geffen School of Medicine at the University of California Los Angeles.
While the protective role of antibodies against infection isn’t fully understood, they are generally considered a good representation of some protection against infection in general, according to the report.
On April 24, the World Health Organization (WHO) addressed the question of immunity passports in the context of Covid-19, writing in a statement, “There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection.” It’s still not known if people can be infected more than once with the novel coronavirus. But there are other, related coronaviruses that cause common colds, and people can and do catch those repeatedly.
In another study from King’s College London showed that the level of antibodies may drop to a degree that makes them undetectable as soon as three months after infection. However, the body also mounts other forms of immunity responses, including from so-called T-cells, which appear to play a role in protecting against reinfection with Covid-19.
In Sweden, the nation’s top health authority said on Tuesday that people who have had the virus are likely to be immune for at least six months after being infected, whether they’ve developed antibodies or not. In new guidance, the Swedish Public Health Agency said it’s now considered safe for individuals who’ve been infected to come into contact with people in high-risk groups.
A survey of people in Spain released earlier this month found similar results.