BENGALURU: With Chief Minister BS Yediyurappa reinfected with Covid-19, experts say there are high chances of antibodies waning faster, and also new variants playing a role.
However, the country does not have enough data to prove that reinfections are happening in large numbers, and to attribute the reason to variants, they say.
“The first infection does not provide strong immunity unlike measles, polio etc, where one infection is good protection. You can get respiratory tract infection a second time. According to a recent report, there is a 4.5 per cent chance of reinfection,” said Dr Jacob John, renowned virologist and former professor at CMC Vellore.
Dr John said mutation occurs on the virus’ spike protein, which almost certainly makes it more effective at binding with human receptor cells.
Some of the variants carry another mutation, suspected of reducing the immunity acquired either by a past infection (with an increased possibility of reinfection), or by vaccines.
However, the infection may be mild, he added. Experts claim that while there’s a lot of uncertainty and unclear clinical evidence, studies now point out that not only is reinfection a true threat, some high-risk groups, particularly those above 65 years of age, face the highest risk of getting reinfected by Covid-19.
“From waning immunity to pre-existing medical illnesses, there are many factors that make people prone to Covid severity. ICMR was doing a study, recalling people with Covid and checking on reinfections, but I am not aware of the results. However, many studies point to waning antibodies,” explained Dr Giridhara R Babu, senior epidemiologist and member of the Covid-19 Technical Advisory Committee.
Current clinical evidence suggests that natural immunity after Covid lasts for at least 6-8 months. However, different people can display different responses.
Experts also claim that age-related diminishing immunity could put the elderly at risk of getting reinfected, and more prone to complications the second time.
Meanwhile, doctors agree that there is no data on how many reinfection cases have happened.
“Since CM Yediyurappa is a public figure, data is available. ICMR is doing a study but so far, there is no data available. About 5 per cent of patients could be reinfected,” said Dr V Ravi, nodal officer for INSACOG and former dean at Dept of Neurovirology, NIMHANS.
A longitudinal cohort study in India, co-authored by Dr Shantanu Sengupta, professor, Institute of Genomics and Integrative Biology (IGIB) found that some people who had Covid- 19 lacked meaningful immunity against the coronavirus to prevent reinfection months later.
Dr Shantanu says, “The study shows that if previously infected people are exposed to high viral loads months after infection, then 20%-30% of people may not have immunity as they are unable to neutralise the microbe and could get reinfected. Similar observations have been made in a study undertaken in Denmark.”
Studies are now underway to understand the presence and activity of memory T cells which can prevent the infection from progressing to severe disease.