Covid-19 antibodies found in 72% samples, says ICMR study

Neutralising antibodies against SARS-CoV-2, which causes Covid-19, were found in 72% of the samples tested at an Indian Council of Medical Research (ICMR) institute, according to a study published in the Indian Journal of Medical Research (IJMR). The study found antibodies were also present in asymptomatic Covid-19 patients.

Neutralising antibodies defend cells from the virus.“…to say anything conclusively about protection against re-infection needs to be studied further,” said one of the authors of the study, requesting not to be identified.

A total of 343 blood samples, of which 89 were positive, 58 negative for Sars-Cov-2, 17 cross-reactive, and 179 serum from healthy individuals were collected and tested at ICMR’s National Institute of Virology in Pune from March to May.

“Among 89 serum samples from SARS-CoV-2 real-time RT-PCR confirmed patients… 64 (71.9%) were found positive and the remaining 25 serum samples (28.1%) negative,” says the study. “Of the 89 COVID-19-positive patients, 59 (66.3%) were symptomatic and 30 (33.7%) were asymptomatic.”

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Serum samples from Covid-19 confirmed patients (n=89) using real-time reverse transcription-polymerase chain reaction (RT-PCR) in Pune and Alappuzha in Kerala were taken for the study.

The symptomatic patients had cough in 48 cases (81.4%), fever in 36 (61%), sore throat in 16 (7.1%), breathlessness in 11 (18.6%), body ache in 9 (15.3%), headache in 5 (8.5%), nasal discharge 2 (3.4%) and diarrhoea in 2 (3.4%).

Of the 59 symptomatic patients, 42 (71.2%) showed the presence of antibodies. Among 30 asymptomatic patients, 22 showed them (73.3%). Among the 25 (28.1%) neutralising antibody negatives, 11 patients were positive (7 symptomatic and 4 asymptomatic), according to the researchers.

Samples were collected within 2 weeks after RT-PCR confirmation from 58 Sars-Cov-2 RT-PCR-negative patients.

“Understanding NAb [neutralising antibody] response among Covid-19 patients is a crucial requirement because the presence of neutralizing antibodies would provide greater assurance of protection in the absence of approved and validated preventive and therapeutic options… The role of cellular immune responses (T cells or cytokines) in the recovery of such patients needs to be explored,” the study says.

“More systematic studies with controlled follow up of patients and titration of NAb among the recovered patients will provide useful information for passive antibody therapy against SARS-CoV-2 virus infection. Further, it is pertinent to study the protective role of NAb during reinfection in recovered Covid-19 patients.”

Experts say that merely detecting antibodies is not enough.

“What is crucial is to know the quality of antibodies, and whether these offer immunity against the disease, and for how long,” said Dr Lalit Kant, former head, epidemiology and communicable disease division, ICMR.

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