WHEN COVID-19 vaccines were first being rolled out in December, many Americans were reluctant to get a jab, fearing that they might be unsafe or have harmful side-effects. At the time, such concerns were not unusual. But according to a new poll, Americans’ continuing scepticism of covid-19 vaccines now makes it an outlier among other rich Western countries. A survey conducted between August 24th and 30th by Morning Consult, an American pollster, found that 28% of Americans say they do not plan to get vaccinated or are unsure whether they will do so, more than double the average for the 15 countries surveyed. Only Russians are less enthusiastic.

Americans’ distrust has remained stubbornly high for months. As shots went into arms with few reports of side-effects, hesitancy in countries such as Australia, Japan and South Korea dropped. It fell in America too, but not by nearly as much. Between March 22nd and August 30th, the share of American adults saying they were unwilling or uncertain about getting vaccinated fell from 37% to 28%; in France, by contrast, that number fell from 49% to just 14%. Some demographic groups have been easier to convince than others. According to Morning Consult, confidence has risen more sharply among Democrats than Republicans and Independents, and among black and Hispanic Americans more than among whites.

The recent surge in covid-19 cases across the country, fuelled by the highly infectious Delta variant, may do little to change sceptics’ minds. The rate of vaccine hesitancy has held steady in many of the states where Delta has hit hardest in recent months. And Morning Consult’s poll suggests that it is those who were once uncertain who have come around, rather than those who are adamantly opposed to vaccination. Controlling covid-19 will require finding a way to convince these holdouts. The larger the population that remains unvaccinated, the larger the petri dish from which potentially more transmissible, vaccine-resistant and deadly mutations can arise.