Here’s what to know about breakthrough cases in the context of the Delta variant and what scientists are doing to track the vaccines’ efficacy: you can get COVID-19 even if you’re vaccinated, but it’s rare and likely to be mild. Don’t panic. Research shows the current vaccines are holding up well against the delta variant. For instance, data from the U.K. suggests the Pfizer vaccine is 88% effective at preventing symptomatic COVID-19 from the delta variant after two doses. And an earlier study from the U.K. found it is 96% effective against hospitalization. Bottom line: Vaccination is still key.