Seropositivity rate, indicating Covid immunity, stands at 97% among Tamil Nadu's elderly

Chennai: With the number of Covid-19 cases witnessing an increase in many parts of the world, a serosurvey conducted by the Tamil Nadu Health Department in April this year has found that 97 per cent of the elderly in the state have “protective levels” of immunity to Coronavirus.

This is the fifth serosurvey conducted by the Health Department since the onset of Covid-19 in 2020 with the immunity level in October 2020 standing at 32 per cent, coming down to 29 per cent in April 2021 at the height of the Covid second wave, and jumping to 70 per cent in August 2021 and further increasing to 87 per cent in December 2021, following massive vaccination drive.

The fifth serosurvey analysed 1214 samples tested for SARS CoV-2 IgG and the protective levels of immunity were found to be 97 per cent. The prevalence of protective level of SARS CoV-2 IgG is very high and significant even after 3 years of gap in conducting the Phase V of the serosurvey, the survey added.

A total of 3,643 blood samples were collected from elderly persons as a part of the Elderly Panel Survey conducted in Chennai, Tiruvallur, Trichy, Tiruvannamalai, Dharmapuri and Kanyakumari districts.

“Effective vaccination drives implemented by the Government of Tamil Nadu might be responsible for the high level of protection against SARS CoV-2 virus. In addition, natural infection and subclinical infection due to the weakened circulating Omicron sub lineage of SARS CoV-2 Virus could have also enhanced the development of antibodies,” the survey said.

Due to the high seroprevalence of SARS CoV-2 IgG in Tamil Nadu, SARS CoV-2 virus could not cause severe illness and deaths are almost nil in Tamil Nadu, the survey added.

Public health expert Dr K Kolandaswamy told DH that the results of the fifth serosurvey showing immunity levels of elderly at 97 percent is a welcome development.

“This means 97 out of 100 elderly in Tamil Nadu have high immunity levels vis-à-vis Covid-19. This means the intensity of the virus will be less on the population and even if infection occurs, the symptoms will be mild and they will recover soon,” he told DH.

He also said the higher percentage in the serosurvey can be attributed to the robust vaccination drive in the state.

In May, the number of people infected with Covid-19 virus more than doubled but the state government appealed to people “not to panic” as the state’s surveillance mechanism was “robust” that can detect any unusual increase in the number of such cases.

The development led to concerns with countries like Singapore already reporting a spurt in the number of people infected with the virus. Tamil Nadu reported about 38,086 deaths during the first and second waves of the Covid-19 between 2020 and 2022.

In the last week of May, the government also asked district authorities to step up disease surveillance and implement proactive measures to ensure early detection, reporting, and response to cases of Influenza-Like Illness (ILI) and Severe Acute Respiratory Infections (SARI).