Seventy per cent of people in Tamil Nadu have COVID-19 antibodies, the latest sero survey - the third since last year - revealed.
In April, the second sero survey had shown that only 29 per cent of the state's population had the antibodies.
Chennai and Coimbatore, which have been the hotspots, have reported the seropositivity at 82 per cent and 71 per cent in the third sero survey conducted between July and August. The Virudhunagar district is at the top spot in the list with 88 per cent of the population.
In April, a 3 per cent drop - as compared to the first survey (32 per cent) - had raised concern that the population turning more vulnerable to coronavirus.
Health Secretary Dr J Radhakrishnan told NDTV: "The current significant rise is due to the natural immunity among recovered patients after the second wave peaked and a spike in vaccination."
Seropositivity is a measure of antibodies present in the body that can protect against COVID-19.
Four districts - including Karur, Nilgiris, Ariyalur and Perambalur - have less than 60 per cent seropositivity rate.
Authorities are intensifying the vaccination drive in these areas. Health Minister Ma. Subramanian said, "We have sent more doses to these districts for the mega vaccination drive on Sunday."
Explaining the process, a statement from the state's health department says 24,586 samples were collected from 827 clusters and 17,090 persons had IgG antibodies against SARS -Cov-2 Virus.
While the seropositivity results certainly puts Tamil Nadu in what health officials call "a safe zone"; experts say there is no protection against any possible new variants.
With 5 crore doses, only 22 per cent of the population has been fully vaccinated. The state is seeing around 1,500 cases every day and it can't let its guard down yet.
Tamil Nadu has logged over 26.7 lakh coronavirus cases so far, and over 35,000 deaths since the start of the pandemic.
Covid Cases Up In North, Clusters In Chennai Colleges As Students Return: Minister Tamil Nadu Reports 26,533 New Covid Cases; 5,246 In Chennai New Covid Cases Drop Below 30,000 In Tamil Nadu, 5,973 In Chennai Alone US Millionaire, Who Died By Suicide, Owed $34 Million With $8,000 In Bank Elderly Man Slapped, Abused On Train Over Suspicion Of Carrying Beef Manipur Chief Minister Slams Tejashwi Yadav Over "Racist" Jab At Himanta Sarma 8 Killed After Bus Carrying 47 Overturns In US State Of Mississippi: Report Trump "Disrespected Sacred Ground' At US Military Cemetery: Kamala Harris Top 10 US Universities Based On Forbes Rankings 2024 Track Latest News Live on NDTV.com and get news updates from India and around the world.