New York state is alerting all other parts of the US about a new mystery syndrome that appears to be related to Covid-19 and is causing severe illness and even death in very young children. At his coronavirus briefing on Sunday, Governor Andrew Cuomo said officials were “putting on notice” the health departments of all other 49 states. So far three children have died – a five-year-old in New York City, a seven-year-old in Westchester county and a teenager in Suffolk county in Long Island. All three showed signs of blood vessel inflammation, and also proved positive for the novel coronavirus. Cuomo said 85 cases of Covid-related illness in children were now being investigated by New York, up from 73 on Saturday. Two other deaths are being looked at. The syndrome has puzzled health experts because it appears to be striking young children largely in the toddler to elementary school age, who had been thought to be largely unaffected by coronavirus. The symptoms are also unusual. Instead of respiratory problems normally associated with Covid-19, the children are experiencing inflammation of blood vessels or the heart. Their symptoms are similar to toxic-shock syndrome and Kawasaki disease, an illness with no known cause that mainly affects children under five. Cuomo opened up the possibility that several more children may have been hit by the mystery illness without health workers recognising what was happening. “It’s possible that these cases were coming in and were not diagnosed as related to Covid, as they don’t appear as Covid,” he said. That is why New York is moving quickly to make sure all other states are on the look-out for the syndrome, Cuomo said, adding: “It may even be probable that this exists in other states and we want to make sure they are aware of it.” In an attempt to better understand the new syndrome, the state is partnering with genetic researchers at the New York Genome Center and Rockefeller University to carry out genome and RNA sequencing. The scientists hope their studies will provide clues as to the genetic basis of the illness.