THIRUVANANTHAPURAM: As many as 22 persons who returned to the state from abroad tested positive for Covid-19 in Kerala after April 5, their incubation period ranging from 14 to 26 days, which vindicates the state’s decision to disregard the WHO-mandated 14-day quarantine norm and extend it to 28 days. International flights to Kerala stopped on March 22 and April 5 was the cut-off date for the 14-day quarantine.A 40-year-old from Kannur, who returned from Dubai via AI Express IX 346 on March 17, tested positive on Sunday, 26 days later. An 11-year old boy who reached Kannur from the UAE on March 15 tested positive on the 24th day, on April 8. Of the cases reported on Monday, a Palakkad native had reached the state on March 22 and tested positive on the 23rd day.The development of symptoms after 14 days poses a huge challenge for the state as nonresident Keralites are expected to return once travel options are available. The state has already announced that it will bear the expenses of testing and quarantine of returning NRKs.Kerala had by the first week of March decided to extend the quarantine period to 28 days while it is 14 days in the rest of the country.