Patients recovering from Covid-19 may lose their immunity within a few months, says a study published on Monday by a team of researchers at King's College London. The study therefore suggests that immunity - capable of protecting the body against new infections - cannot be taken for granted after the disease is overcome for the first time. This is the case for other viruses, such as the flu.
The discovery could complicate the development of an effective long-term vaccine.
"If the infection provides levels of antibodies that decrease in two to three months, the vaccine potentially will do the same thing and a single injection may not be enough," Katie Doores, the study's lead author, told The Guardian.
It is the first longitudinal study of its kind, according to the British newspaper. The immune response of more than 90 patients and healthcare professionals in the NHS system (equivalent to the UK SUS) was analyzed and found that the levels of antibodies that can destroy the virus peaked around three weeks after the onset of symptoms, but shortly thereafter it fell.
Blood tests revealed that while 60% of people achieved a "potent" antibody response at the height of their battle with the virus, only 17% maintained the same potency three months later. Antibody levels dropped 23 times in the period. In some cases, they have become undetectable.
The immune system has other ways to fight the coronavirus , but if antibodies are the main line of defense, the results suggest that people can become infected again in seasonal waves and that vaccines may not protect them for long.
Until more information is learned, "even those with a positive antibody test - especially those who don't know where they were exposed - should continue to exercise caution, social detachment and use an appropriate mask," warns James Gill, honorary professor at Warwick Medical School.