The seasonal flu vaccine may offer partial protection against the pandemic H1N1 swine flu, but not enough to prevent a person from catching the swine flu.
To evaluate the association of 2008-9 seasonal trivalent inactivated vaccine with cases of H1N1 flu, researchers studied 60 patients with laboratory confirmed influenza A/H1N1 and 180 controls (of the same age and socioeconomic status) with other diseases (not influenza-like illness or pneumonia) living in Mexico city. Some of the patients reported having received a 2008-09 seasonal flu shot.
It was found that those who had received a seasonal flu vaccine and were infected with the H1N1 flu had significantly milder course of illness than those who had not received the seasonal flu vaccine. The seasonal flu vaccine may boost existing antibodies in those who have had a similar flu virus or a vaccination against seasonal flu.
But the researchers cautioned that people who have received a seasonal flu vaccine should not assume they are protected from the pandemic H1N1 flu or its complications.
The researchers recommended that people should receive both seasonal and H1N1 vaccines.