New flu vaccines are available for 2013, and though they cost more, they also offer protection against more strains of the flu virus.

Until now, seasonal flu vaccines only protected against three strains of the flu virus: two strains of influenza A, which usually causes more cases and more severe sickness, and one of influenza B, which is less common but comes in multiple forms, Reuters reports.

The new flu vaccines include protection against a second strain of influenza B, which experts expect will prevent the vast majority of type B infections, Reuters writes.

However, this extra protection comes with a price - contracts struck with the U.S. Centers for Disease Control and Prevention (CDC) confirm a hefty price increase for the new four-strain flu vaccine. GSK's quadrivalent Fluarix, for example, could cost $12.03 per dose against $8.08 for the standard version, according to the agency's website, Reuters reports. This would mean about a $4 increase for the new vaccines.

These four-strain flu vaccines may be the only shots available within two years, predicts Paul Offit, chief of infectious diseases at the Children's Hospital of Philadelphia, according to Reuters.

Most of the four-strain flu vaccine business in 2013/14 will come from the United States, Reuters notes, where the CDC expects four-strain vaccines to account for around 23 percent of the 135-139 million doses that manufacturers are likely to make for the country.