For the first time, this winter THL has monitored the effectiveness of flu vaccines in real time by cross-referencing the national vaccination registry with flu cases data in the communicable diseases registry. In parallel, Swedish researchers began registry-based monitoring in Stockholm County.
It was found that at the start of the flu season in December the effectiveness of vaccines in Finland was relatively good, at about 50 percent. By the start of the year, the effectiveness had clearly fallen, to 32 percent. This was in the same range as the 28 percent effectiveness seen in Stockholm at the same time.
In both Finland and Sweden, nearly all early cases were influenza A(H3N2). As the season progressed the number of variations (subclades) were found to have increased. The genetic changes likely explain the decrease in the effectiveness of inoculations.
A report by the Finnish-Swedish research group was published in the medical journal Eurosurveillance on Thursday.
So far this winter only about two dozen cases a week of B-type flu have been registered in Finland.
"It is still too early to say if the number of B-type flu cases will increase during the spring, but the vaccines also include protection against the B-type virus," says Niina Ikonen, a specialist at THL.