- People who developed only mild to moderate symptoms tended to produce fewer neutralizing antibodies than people with severe cases of COVID-19.
- A recent study found that 65 days after infection had passed, only 17 percent of participants still had potent levels of neutralizing antibodies in their blood.
- Early research has found that people who’ve recovered from COVID-19 do carry SARS-CoV-2-specific T cells
Since SARS-CoV-2 was first identified in December 2019, the novel strain of coronavirus has caused nearly 14 million cases of COVID-19 worldwide.
A growing body of research suggests that when someone contracts SARS-CoV-2, their immune system’s production of antibodies against the virus tends to quickly peak — and then rapidly decline.
These findings have contributed to concerns about the possible risk of reinfection in people who’ve already recovered from COVID-19.
“More and more studies actually show that individuals, especially with mild disease, tend to lose these antibodies over time,” Kamran Kadkhoda, PhD, medical director of the immunopathology lab at Cleveland Clinic in Cleveland, Ohio, told Healthline.
“Whether that means they’re at risk of reinfection? That remains a possibility,” he said.
Mild infections might confer less immunity
In a new study reported in a preprint paper on the website MedRxiv, researchers found that levels of neutralizing antibodies against SARS-CoV-2 peaked within about 3 weeks of people developing symptoms.
Within those first 3 weeks, 60 percent of participants in the study developed “potent” neutralizing antibody responses against the virus.
By the time 65 days had passed, only 17 percent of participants still had potent levels of neutralizing antibodies in their blood.
People who developed only mild to moderate symptoms tended to produce fewer neutralizing antibodies than people with severe cases of COVID-19.
Neutralizing antibody levels also tended to drop to lower levels in people who developed only mild to moderate infections. In some of them, no neutralizing antibodies could be detected by the end of the study.
This study was conducted by researchers from King’s College in London, England. Their report of the study has not yet gone through peer review, but other peer-reviewed research has yielded similar findings.
Other immune processes are also involved
In coverage of the King’s College study, some media outlets have warned that immunity to COVID-19 may be “short-lived” and herd immunity may “never arrive.”
But according to Dr. Stuart P. Weisberg, more research is needed to understand how the immune system responds to SARS-CoV-2 and how long immunity to the virus may last after someone recovers from infection.
“Immune protection involves a complex cellular and serological response that cannot be distilled down to production of neutralizing antibodies,” Weisberg, an assistant professor of pathology and cell biology at Columbia University Irving Medical Center in New York, New York, said.
In addition to antibody-producing B cells, other types of B cells and T cells also play important roles in warding off viral infections.
For example, memory T cells help the immune system recognize and respond to viruses that it’s already encountered before.
“After viral infection, a small population of long-lived memory T cells remain within the previously infected tissue and continue to circulate throughout the body,” Weisberg explained.
“These memory cells have the potential to rapidly reactivate upon seeing the virus again, which helps make the second infection less severe than the first,” he added
More research is needed
Early research has found that people who’ve recovered from COVID-19 do carry SARS-CoV-2-specific T cells. However, more research is needed to learn how much protection those T cells may provide against reinfection.
“We know that memory T cell responses are generated after SARS-CoV-2 infection, but we do not know how long they last, how much protection the T cells provide, or how quickly they can re-activate upon reinfection,” Weisberg told Healthline.
“All of these questions require further study,” he continued.
Additional research is also needed to learn what level of neutralizing antibodies is required to protect against reinfection with SARS-CoV-2.
It will take time for investigators to answer these questions and determine how long immunity against SARS-CoV-2 may last.
Multiple doses of vaccine might be needed
If it turns out that immunity against SARS-CoV-2 is short-lived, that will limit the potential for communities to naturally develop herd immunity.
It will also pose challenges to the development of a long-lasting vaccine.
“Durability of vaccine protection will depend entirely on the vaccine characteristics,” Weisberg said.
“However, many vaccines require boosting in order to reactivate the memory immune response and re-establish optimal protection,” he continued.
Early results from the first human clinical trial of a SARS-CoV-2 vaccine suggest that multiple doses might be required to prevent infection.
“There’s a good chance that revaccination every season or at least more than one season [will be] required, which is challenging,” Kadkhoda said.
“At the global level, that would be a lot of vaccines,” he added.
Kadkhoda expects that physical distancing and mask-wearing will remain mainstays of COVID-19 prevention for the foreseeable future.
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