COVID-19 HAS come roaring back in America. Fuelled by the more-transmissible Delta variant, new cases and hospitalisations have shattered records across the South and some parts of the Northwest. Florida, Louisiana and Mississippi have been hit the hardest. Although some vaccinated people have fallen ill, the vast majority of new cases are among the unvaccinated: people ideologically opposed to the jab or reluctant to get it for fear of exacerbating underlying health conditions. With children returning to packed schools around the country—and vaccines still unavailable to children under 12—concerns about the virus’s progress are growing.

According to The Economist’s weekly polling with YouGov, an online firm, worry about the Delta variant has jumped in recent weeks (see chart). The percent of adults who say they are “very” or “somewhat” worried rose from 47% in late June to 58% this week. Yet this fear is accompanied by an only modest increase in favourable attitudes to vaccination. In YouGov’s data, the percentage of people saying they have or will get the jab increased only from 69% to 72% over the last month, a rise well within the survey’s margin of error.

Concerns about in-school transmission are resurfacing. The Centres for Disease Control and Prevention, the country’s health-protection agency, previously suggested that school reopenings did not increase infection rates in the general population, but it is unclear whether this will remain true as the Delta variant spreads. Although the majority of the public thinks that children should be required to wear masks to school (and a plurality wants youngsters vaccinated), policies vary widely and are often driven more by politics than epidemiology. Few if any schools have standardised systems for testing and reporting positive cases if an outbreak happens. Yet despite the spectre of crowds of pupils packing maskless into school auditoriums, many parents are still unenthusiastic about vaccinating their children. Just over half of parents with children old enough have got theirs vaccinated or plan to do so.

The Food and Drug Administration, America’s medicines regulator, officially approved the Pfizer-BioNTech vaccine for those aged 16 and over this week, while an increasing number of employers, both public and private, are requiring their employees to get vaccinated. With luck, both will help to sway some holdouts. But YouGov’s polling from August 2nd found that only one out of ten adults opposed to the vaccine said they would get the jab if the FDA authorised it. And the fact that political persuasion is the single most significant predictor of whether an American has been vaccinated may undermine the hope that the reluctant will be persuaded. The more people who can be vaccinated but do not, the greater the chance of dangerous mutations of covid-19 emerging.