Indian Council of Medical Research (ICMR) suggested that people with a second bout of Covid-19 should be considered cases of reinfection if their first bout was at least 102 days prior to their latest positive test result and they had at least one negative test in the period between.
The study was based on telephonic interviews of 1,300 people, 4.5% of whom appeared to have been infected by the virus twice. The government has been working on a definition for ‘reinfection’ of cases since October. The study was published online by the Cambirdge Epidemiology and Infection journal.
The 4.5% who were found infected were people infected in the first wave. “This is an averaged out figure over a period of about eight months— January to October, 2020—, which will vary with behaviour and intensity of epidemic,” said Dr Balram Bhargava, director general, ICMR.
According to the study, the authors said: “Taking available evidence into consideration, re-infection with Sars-CoV-2 in our study was defined as any individual who tested positive for SARS-CoV-2 on two separate occasions by either molecular tests or rapid antigen test at an interval of at least 102 days with one negative molecular test in between. In this archive based, telephonic survey, 58 out of 1300 individuals (4.5%) fulfilled the above mentioned definition”.
Interestingly, the study did not look at a genomic analysis of the first and second infections, the only sure way of proving a case of reinfection.
The study, the authors added, was meant to “develop an epidemiological case definition of possible Sars-CoV-2 re-infection and assess its magnitude in India… The epidemiological case definition… was developed from literature review of data on viral kinetics… While Sars-CoV-2 re-infection is still a rare phenomenon, there is a need for epidemiological definition of re-infection for establishing surveillance systems and this study contributes to such goal..,” the paper said, adding that “obtaining genomic evidence is resource intensive and not always feasible”.
The globally accepted benchmark for reinfection is less than 1%.
The US Centers for Disease Control and Prevention considers the duration of 90 days between two positive Sars-Cov-2 infections, along with genomic evidence of reinfection as an investigative criterion to understand the phenomenon of reinfection.