New Delhi: A day after India reported two cases of Omicron, 18 travellers from “at risk” countries tested Covid-19 positive and were being screened for the presence of Omicron.Health Minister Mansukh Mandaviya informed the Lok Sabha today that 18 travellers out of the 16,000 screened from 58 flights had tested Covid-positive. The minister’s reply came moments after the Centre issued another advisory to states flagging the need for aggressive testing, contact tracing and expanded vaccination in the wake of emerging evidence of Omicron’s enhanced transmissibility.“The current evidence, which is evolving, suggests increased transmissibility of Omicron. We must be extra vigilant in enforcing public health measures to contain its spread,” Union Health Secretary Rajesh Bhushan said in the letter to all Chief Secretaries.The letter advised states to ensure self-declaration forms of all passengers from “at risk” nations uploaded on the government’s Air Suvidha portal, enhanced testing and tracing. The other measures include testing all contacts of positive passengers within 72 hours.