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SINGAPORE, March 25 — Antibodies that protect against Covid-19 wane at different rates, lasting mere days in some individuals but remaining in others for decades, a Singapore study has found. The findings by scientists from Duke-NUS Medical School, the Nation…

Annual vaccinations could be necessary to prevent future outbreaks of Covid-19.  TODAY pic
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SINGAPORE, March 25 Antibodies that protect against Covid-19 wane at different rates, lasting mere days in some individuals but remaining in others for decades, a Singapore study has found.
The findings by scientists from Duke-NUS Medical School, the National Centre for Infectious Diseases (NCID) and the Agency for Science, Technology and Research (A*Star) Infectious Diseases Labs show that not everyone who has recovered from Covid-19 is immune from reinfection.
And if immunity provided via vaccines wanes like naturally-produced antibodies from a past infection, then annual vaccinations could be necessary to prevent future outbreaks of Covid-19.
Highlighting these in a press release on Wednesday (March 24), Duke-NUS, NCID and A*Star said the research was important for policymakers planning vaccination programmes and pandemic exit strategies. 
But they added that further studies would be needed to clarify the findings as vaccine programmes are rolled out.
The study was published in international medical journal The Lancet Microbe on Tuesday.
The researchers followed 164 Covid-19 patients in Singapore for up to nine months, analysing their blood for neutralising antibodies the proteins responsible for defending cells from Covid-19 pathogens.
Data collected from these patients at the six-month mark was used to establish a machine learning algorithm that allowed the scientists to predict how the protective antibodies wane over time.
At nine months, data was collected from the patients again to validate the predictions.
The findings suggested that the antibodies longevity can vary greatly, and it is important to monitor this at an individual level, said Professor Wang Linfa from Duke-NUS Emerging Infectious Diseases Programme, who is a corresponding author of the study.
This work may have implications for immunity longevity after vaccination, which will be part of our follow-up studies, said Prof Wang.
Besides studying neutralising antibodies, the study also looked at patients T-cell
T-cells are a type of white blood cell that works with antibodies to eradicate pathogens such as the Sars-CoV-2 virus that causes Covid-19.
The researchers found that individuals may still be protected from Covid-19 if they have robust T-cell levels, even if their level of neutralising antibodies is low.
Associate Professor David Lye, Director of the Infectious Disease Research and Training Office at NCID, who is also a corresponding author of the study, said the presence of T-cell immunity provides hope of longer-term protection against Covid-19.
More studies and time for epidemiological and clinical evidence are required to confirm this, he added. TODAY