COVID-19 vaccines rolling out around the world weren’t compared to each other in studies, so it’s hard to tell how they might differ in effectiveness. But experts say they’re alike on what matters most: preventing hospitalizations and deaths. Although studies conducted before the vaccines were rolled out found varying levels of effectiveness, they don’t offer apples-to-apples comparisons. The Pfizer and Moderna vaccine studies, for example, counted a COVID-19 case whether it was mild, moderate or severe. The study for Johnson & Johnson’s vaccine didn’t count mild illnesses and was done when mutated versions of the virus were a bigger concern.