A new way to grow the flu virus, a step which might speed up production of vaccines generally, has been developed by researchers at the University of Wisconsin.

Reverse genetics is one of many processes used to create viruses that in turn are made into vaccines. The process uses strings of genes called plasmids placed into cells — usually eight plasmids. But Yoshihiro Kawaoka and colleagues at Wisconsin report a method using just one plasmid.

Their findings were released Monday in the online edition of Proceedings of the National Academy of Sciences.

By reducing the number of plasmids needed, they increase the efficiency of virus production and potentially could speed up vaccine production, Kawaoka said.

Karen Lacourciere, a researcher at the National Institute of Allergy and Infectious Disease, said the method shows promise in producing virus strains.

But, she added, the system hasn't been used to make a vaccine strain yet so it remains to be seen how much of an improvement it would be.