Prime Minister Narendra Modi -- after a review meeting on Covid today amid the surge in China -- did not make masks mandatory, but advised their usage. He also emphasised the need for strengthened surveillance with focus on genome sequencing and increased testing for Covid. There has been concern after four cases of the virus variant playing havoc in China was detected in India. One of the cases surfaced as far back as July, the others in September and November. The government has said there is no cause for panic. Sources said the patients had recovered with treatment at home. PM Modi, however cautioned against complacency, saying states should ensure operational readiness of hospital infrastructure -- including oxygen cylinders, PSA plants, ventilators and human resources.