Influenza vaccine less effective than expected

Experts of the HZI comment on the situation and explain the causes

The effectiveness of this season's influenza vaccine appears to be less than optimal. The vaccine must be expected to be less effective against one of the three circulating types of the virus, as reported by the Robert Koch-Institute (RKI). Prof Klaus Schughart, head of the "Infection Genetics“ department, and Prof Carlos Guzmán, head of the "Vaccinology" department at the Helmholtz Centre for Infection Research (HZI) in Braunschweig comment on the current situation and the backgrounds.

In recent weeks, the media have been full of headlines like "Influenza: Vaccination less effective than in the past", "Influenza epidemic on its way: Flu viruses spreading" or "Troublesome vaccine: Thousands of Germans afflicted by influenza". The reason underlying the reduced effectiveness is the H3N2 variant circulating this year, which is slightly changed from the vaccine virus. "The strain of influenza used for vaccine production is selected one year ahead of time. For this purpose, a forecast is made on the basis of the previous year and the influenza viruses circulating at that time. Although the forecasts are usually very good, unfortunately this is not always the case," says Schughart.

Even though the forecast is based on data sent to the WHO by more than 100 national reference laboratories throughout the world. This data serves as the basis of the discussions of experts leading to the selection of the virus strain for vaccine production. "Despite extensive efforts, it remains very difficult to forecast so early exactly those influenza subtypes against which the vaccine needs to be effective," says Guzmán. "This means that we need to continue the work on better forecasting methods and also need to search for new vaccines that provide protection against all influenza A types."

It is too late for the ongoing year, though, and the influenza epidemic is expected to be more pronounced than in recent years. "The flu epidemic has already run its course in the USA and the virus circulating there seems to cause more severe symptoms than previous epidemics," says Schughart. "The peak has not been reached in Germany yet. But we have to expect a similar course of disease." In the past three weeks, the number of influenza infections in Germany has risen strongly, but the peak is expected only in the next three weeks.

Although the current vaccine is less effective than hoped, HZI researchers agree that vaccination is advisable anyway. "Partial protection is better than no protection. Therefore, the vaccination should be done even if it provides less-than-expected protection against one of the strains," says Guzmán. "In addition, this year's vaccine protects against a variety of viruses - including the seasonal H1N1 virus, influenza B virus and the H3N2 virus in question. The protection against H1N1 and influenza B viruses is good," Schughart says.