Flu shot for next winter should contain same strains as this year's: WHO

No major virus mutations expected

Next winter’s flu vaccine will be a rare repeat of this year’s formula.

Experts who advise the World Health Organization recommended no change for the vaccine for the Northern Hemisphere winter of 2014-15 at a meeting this week in Geneva.

Flu viruses mutate often and it is common to have to change several of the viruses included in the vaccine from one year to the next.

But analysis of viruses collected from around the world shows there haven’t been any major changes.

Dr. Nancy Cox of the U.S. Centers for Disease Control says that will make the job of producing the vaccine easier for manufacturers, who know how to maximize growth of these viruses.

But Cox says holding pat for one year may make things tough for the following year, because by that point there may be multiple changes needed.

“Next time could be very challenging. Several different components could change,” says Cox, who heads the CDC’s influenza division and took part in the strain selection meeting.

This committee of experts meets twice a year, in February to select the vaccine viruses for the following Northern Hemisphere winter and in September to do the same for the Southern Hemisphere.

Depending on the manufacturer, flu vaccines contain three or four components. The standard vaccine protects against three strains of flu viruses, two influenza As — an H1N1 and an H3N2 — and one of two families of influenza B viruses.

In recent years some manufacturers have started to make a four component or quadravalent vaccine which contains the two influenza As and the two B viruses.