The amount of neutralizing antibodies developed by patients after infection with SARS-CoV-2 varies dramatically over time and between individuals. Some people will almost never develop antibodies, while in others the immune response will become stronger over time. A future headache for doctors trying to identify who needs a booster vaccination.
How long is one protected after infection with coronavirus? A few weeks? A few months? Or several decades? At this point, it’s impossible to know for sure, since the epidemic has only been going on for a little more than a year. A recent study published in Science suggests that immunological memory (neutralizing antibodies, B and T lymphocytes) is present for up to eight months after infection. Another US study had suggested that this immune memory could last for years.
In reality, the answer is that it depends on the person. Researchers at Duke-NUS Medical School in Singapore found startling differences in the rate at which antibodies decline: Some patients have no antibodies left after a few days, while in others they may last for decades. The team followed 164 patients in Singapore for six to nine months after their SARS-CoV-2 infection. They analyzed their blood to measure the amount of neutralizing antibodies and T cells and then developed an algorithm to predict the evolution of antibody levels over time.
From 0 to 14,881 days
Patients were then divided into five groups based on their antibody levels:
- The first group (11.6% of patients), called the “negative” group, never developed detectable neutralizing antibodies.
- The “rapidly declining” group (26.8%) had early but rapidly declining antibody levels.
- The “slowly declining” group (29%) retained antibodies for up to six months, but also declined quite rapidly.
- The “persistent” group (31.7%) has relatively stable antibody levels for up to 180 days.
- The “delayed response” group (1.8%) shows a significant increase in neutralizing antibodies during late convalescence.
However, this last group, which raises questions among the authors, is not representative of the population (it includes only three cases). In contrast, the “persistent” group, which accounts for nearly one-third of patients, could have immunity between 326 and… 14,881 days, according to the algorithmic model. That’s a potential protection of 40 years! It’s a prediction that will take a long time to verify, “but it is not completely unrealistic, considering that patients infected with SARS in 2003 still have neutralizing antibodies 17 years later,” the researchers point out.
No antibodies? No reason to panic
However, the patients who have retained the most antibodies are also those who had more severe infections, including high levels of inflammatory cytokines. Conversely, antibody levels drop faster in people who experienced fewer symptoms. But rest assured: even with very few antibodies, you can still be protected from reinfection. In their study, published in The Lancet Microbe, the researchers noted that all patients tested, including those in the “negative group,” had prolonged T-cell immunity for at least six months after initial infection.
This study reminds us that we all respond differently to infections,” says Laurent Renia, a professor at the Singapore Agency for Science, Technology, and Research. It could also call into question vaccination strategy: If vaccine-provided immunity, like that of naturally produced antibodies, wanes, annual boosters may be needed in some people to prevent future Covid 19 outbreaks. Still, the study does not tackle the issue of whether these current antibodies could protect against the newer variants that may appear in the future.