Federal officials said Wednesday they plan to strengthen cautions about a rare side effect of some COVID-19 vaccines — chest pain and heart inflammation, mostly among teenagers and young adults. But in an unusual joint statement, top U.S. government health officials, medical organizations, laboratory and hospital associations and others stressed the overriding benefit of the vaccines. “The facts are clear: this is an extremely rare side effect, and only an exceedingly small number of people will experience it after vaccination. Importantly, for the young people who do, most cases are mild, and individuals recover often on their own or with minimal treatment,” the statement said.