In England, worries about staffing are dire enough that retirees — often older and therefore more vulnerable to severe illness from the coronavirus — have been urged to return to duty. Schools have been advised to merge classes to plug staffing gaps. And in a country that has long resisted the types of precautions taken in countries like Germany, secondary schools are now required to test all their students twice a week — adding to the burden of smaller staffs…

Education staff were more likely than other workers to test positive for the coronavirus late last year and have to isolate, according to numbers from the Office of National Statistics, and in London, many schools had struggled just to make it to the holidays amid staff absences.

Since many schools reopened last week, more than a third of about 2,000 schools surveyed in England had 10 percent of their staff absent on the first day back, according to a poll by NAHT, the school leaders’ union. And 37 percent of schools polled said they were unable to find enough substitute teachers to fill in for those who were ill.