Manufacturers are including the H1N1 or "swine flu" antigens along with those of two other strains in the standard influenza vaccine this year, USA Today reported Saturday.
That has worried at least some people getting the shots, pharmacists say.
"People are somewhat leery about it, but it just happens to be one of three strains in this year's shot," Craig Schury, a pharmacist for Pemberton Pharmacy in Salisbury, Md., said. "It's made the same way as the regular flu shot was last year."
There is normally a mixture of strains in the shots and the majority of his customers weren't concerned, Schury said.
In 2009 manufacturers split their vaccine production between the swine flu and regular flu vaccination.
"I think there's confusion because last year there were two separate shots," Jennifer Berkman, director of student health services for Salisbury University, said. "Epidemiologists look globally at different strains and try to predict which strains are going to impact the U.S. this season."