There's no such thing as "Covid infection". There's SARS-CoV-2 infection, which often causes CoVID-19 disease. Pfizer is saying that their vaccine is effective

There's no such thing as "Covid infection". There's SARS-CoV-2 infection, which often causes CoVID-19 disease. Pfizer is saying that their vaccine is effective at protecting against CoVID-19 disease. They haven't said anything about preventing SARS-CoV-2 infection yet, as far as I can see. The difference is important, because there are vaccines (such as the Salk polio vaccine) that only protect against disease, but not against infection. People get infected and pass on the virus without ever getting sick, so there's no herd immunity.