Chennai, May 27 : District Collectors in Tamil Nadu have begun enforcing Covid-19 protocols in their districts after a marginal increase in the number of infected persons. State Health Secretary J. Radhakrishnan in a letter to the District Collectors on May 26 said the steady surge in Covid-19 cases in Chennai and several other parts of the state indicates that immunity levels are falling. He also mentioned that this would lead to people becoming susceptible to variants, sub-variants and lineages of Covid-19. The health department is worried that apart from institutional clusters like that in IIT Madras and Anna University, family clusters are also developing in Chennai and the adjoining districts of Kancheepuram, Chengalpattu and Tiruvallur. The District Collectors have asked the local level officers, including health officials, to be vigilant and check the infection from spreading. The district administration has also urged the government and private hospitals to conduct checks on people with comorbidities and the elderly. The police have been directed to ensure stringent action is taken against those not wearing masks. The health department in a statement said as of Thursday, 43 lakh eligible people in the state are yet to take the first dose of Covid-19 vaccine while 1.22 crore people have not taken their second dose. As many as 93.74 per cent people of the state have received their first vaccine dose while 82.55 per cent have taken their second dose. /IANS