Some Bradford schools are missing pupils because they travelled abroad with their families, who cannot now get back without paying a hefty bill for hotel quarantine. This is just one of the risks of travel during a global pandemic, says Dr John Wright of Bradford Royal Infirmary, who notes that British travellers may also have contributed to the spread of the virus.
A head teacher tells me that she has a problem with families stuck abroad, in countries on the UK's red list.
British residents who have been in one of these countries have to spend 10 days in quarantine in a hotel when they arrive back, at a cost of £1,750 for a single adult, and much more for families. Those who can't afford it are sometimes staying where they are - perhaps living free of charge with relatives - and this has left noticeable gaps in some classes.
In Bradford, families are mostly stuck in Pakistan, where the majority of the city's Asian population originates, but it's clear that many UK families are also unable to return from India and Bangladesh.
"We didn't know there was any chance of quarantine - we just went," says Inaya Hussain, who flew to Pakistan with her three children, aged between nine and 13, the week before lockdown, because her mother was seriously ill.
But on 9 April Pakistan was put on the UK's red list, because of rising numbers of Covid infections, as was Bangladesh. On 23 April, India was added too.
Lynette Clapham, head teacher at Grove House and Crossley Hall Primary Schools, says she's aware of 11 families who are currently abroad and unable to return, often because of the cost of quarantine.