Longitudinal study finds neutralizing COVID-19 antibodies may last days to decades

Antibodies against SARS-CoV-2, the virus that causes the novel coronavirus (COVID-19) could wane at different rates, lasting for days in some individuals while remaining present in others for decades, according to a new study by the Duke-NUS Medical School, the National Centre for Infectious Diseases, and the Agency for Science, Technology, and Research Infectious Diseases Labs published in the journal The Lancet Microbe.

For the study, the researchers followed 164 COVID-19 patients in Singapore for six to nine months, analyzing their blood for neutralizing antibodies against SARS-CoV-2, T cells, and immune system signaling molecules. They then used this data to establish a machine learning algorithm to predict the trajectories of peoples' neutralizing antibodies over time.

The team was able to categorize people into five groups depending on how long their antibodies lasted. The “negative” group, 11.6 percent of the patients in the study, never developed detectable neutralizing antibodies. The “rapid waning” group, 26.8 percent, had varying early levels of antibodies that waned quickly. The “slow waning” group, 29 percent, tested mostly positive for antibodies at six months. The “persistent” group, 31.7 percent, showed little change in their antibody levels up to 180 days. Lastly, the “delayed response: group, 1.8 percent, showed a marked rise in neutralizing antibodies during late convalescence.

The research showed that the severity of the infection could be a deciding factor in having longer-lasting antibodies. Individuals with low levels of neutralizing antibodies may still be protected from COVID-19 if they have a robust T-cell immunity, the researchers said.

While this study focused on determining the levels of neutralizing antibodies, which are part of the body's comprehensive immune defense system, the other important aspect of an effective immune defense is T-cell immunity. The study found that the patients tested, including those from the negative group, displayed sustained T-cell immunity six months after initial infection. This shows that individuals may still be protected if they have a robust T-cell immunity when the neutralizing antibody level is low, according to the study.

"The key message from this study is that the longevity of functional neutralizing antibodies against SARS-CoV-2 can vary greatly and it is important to monitor this at an individual level,” said Linfa Wang, PhD, corresponding author of the study and professor in emerging infectious diseases at Duke-NUS Medical School, in a statement. “This work may have implications for immunity longevity after vaccination, which will be part of our follow-up studies.”

The findings are important, the researchers said, as policy makers design vaccination programs and pandemic exit strategies. The rate of antibody waning suggests re-infection may occur in subsequent waves of infection, they said. Additionally, the researchers said that if immunity provided via vaccinations wanes like naturally produced antibodies, then annual vaccine administration could be necessary to prevent future outbreaks of COVID-19. Further research will be needed to clarify this as vaccine programs are rolled out.

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