The omicron variant is heightening risks for this little-talked-about demographic: pregnant women.

Left out of early vaccine trials and faced with confusing messages and misinformation on the dangers to their unborn children, a disproportionately large number of pregnant women have steered clear of COVID-19 shots. About 75% of expectant mothers in the U.K. and about 65% in the U.S. remain unvaccinated, making them among the groups most at risk of getting infected and being exposed to severe forms of the disease as the fast-spreading omicron strain sweeps across the globe.

At least 17 pregnant women and four babies have died from COVID-19 in England between May and October, figures published last week show. Over that period, 98% of pregnant women admitted to intensive care were unvaccinated. Also, since July, one in five COVID-19 patients receiving treatment in England through a special lung-bypass machine was an unvaccinated expectant mother.