Seasonal influenza vaccines 2014–2015 provide protection against circulating flu viruses

Vaccination against seasonal influenza is particularly important for older people, pregnant women, those with underlying health problems, such as asthma or cardiovascular disease, and health care workers.

How are influenza (flu) vaccines made each year?

The influenza virus changes constantly. Member States of the WHO European Region therefore conduct influenza surveillance during the flu season. This means that they monitor how the virus is changing and which strains of the virus are circulating. The seasonal influenza viruses currently circulating are the A (H3N2), A (H1N1)pdm09 and influenza B viruses. These strains change constantly.

In February, WHO takes the information that has been provided by Member States, the collaborating centres and other partners and makes recommendations for the vaccine for the upcoming flu season. This recommendation is based on which influenza strains they believe will circulate during the next flu season. This is done as late as possible, while still allowing the vaccine manufacturers sufficient time to produce the vaccine. This enables the prediction of the vaccine’s composition to be as accurate as possible.

Do we always get it right?

Unfortunately, the flu virus does not stop changing at the end of February when the vaccine recommendations are made. The virus continues to circulate and keeps changing. It is sometimes significantly different by the time the vaccine is ready for the northern hemisphere and the vaccine and the virus are no longer a good match. This is known as antigenic drift.

How effective is this year’s flu vaccine?

There are three components of seasonal flu vaccines, known as a trivalent vaccine. First, it contains A(H1N1)pdm09, also known as swine flu. This component is still effective. Secondly, it contains influenza B viruses. These are also effective in this year’s vaccine.The third component this season is an A(H3N2) virus. Unfortunately, it is likely that, in the upcoming season, A(H3N2) viruses will show antigenic drift in relation to the vaccine virus. This means that the vaccine is likely to be less effective.

Should I still have a flu vaccination?

The antigenic drift is likely to have a negative impact on the effectiveness of the A(H3N2) part of the vaccine. However, this part of the vaccine is expected to provide cross protection against A(H3N2) viruses. This may reduce the likelihood of severe outcomes, such as hospitalization or death. The other two components of the vaccine are effective. So it is still important for people to get vaccinated in preparation for the flu season.

Vaccination is particularly important for:

  • older people — the age limit is nationally defined but is set at over 65 in most countries;
  • pregnant women, since vaccination protects them and their unborn babies;
  • people with underlying health problems, such as asthma or cardiovascular disease;
  • health care workers, especially those who work with those most at risk.