As many as 65 percent of people who received flu shots last winter did not get the protection they expected from the vaccines. According to the National Institute for Health and Welfare the THL, the viral anti-agent used for the past three years no longer protects against new strains of the virus.

Helsinki University Hospital's medical chief of infectious diseases Veli-Jukka Anttila said that the last season saw the emergence of an H3N2 type virus, which was rife in senior patients in long term care wards and in primary health care stations. Some of them had received flu shots.

Flu jabs offer variable levels of protection, depending on the season. Their efficacy depends on how well the anti-virals respond to existing viruses.

Drug companies are developing a vaccine that would be effective against all strains of the virus. Until then, although current vaccines aren't 100 percent effective, it's still worth it to take the annual jab, the experts say.

Vaccines to be administered during the next flu season are already being tailored to provide better protection against current circulating virus strains.

According to THL researcher Hanna Nohynek, the shot will cover the new H3N2 strain, the new B-virus and the swine flu virus, giving better protection to vulnerable groups.