WASHINGTON – Mexican researchers say they have some evidence that the ordinary seasonal flu vaccine may offer some protection against the new pandemic H1N1 swine flu — contrary to other studies.
They found that people who had been vaccinated against seasonal flu were far less likely to be sick or to die from H1N1 than people who had not been immunized against seasonal flu.
"These results are to be considered cautiously and in no way indicate that seasonal vaccine should replace vaccination against pandemic influenza A/H1N1 2009," Lourdes Garcia-Garcia and colleagues at the National Institute of Public Health in Cuernavaca wrote in the British Medical Journal.
But they said the findings might offer some good news for people who have been vaccinated against seasonal flu, especially as governments are just beginning to distribute newly made swine flu vaccines.
The new H1N1 swine flu virus is a very distant cousin of the H1N1 seasonal flu virus, which is included in the mixture provided every year in the seasonal flu vaccine.
Most studies have shown the annual vaccine provides little or no protection against H1N1, likely because it is very different.
One study in Canada suggested that in fact people who got seasonal flu vaccines may be more likely to become infected with H1N1, although the World Health Organization and the U.S. Centers for Disease Control and Prevention both expressed doubts about the findings.
Garcia's team studied 60 patients with confirmed swine flu and 180 similar people with other diseases being treated in the Mexico City area.
The Mexican government distributes seasonal flu vaccine.
Only eight people who had been vaccinated against seasonal flu were among the swine flu cases, the researchers reported. They found that 29 percent of unvaccinated people in the study became infected with H1N1, versus 13 percent of vaccinated people.
None of the vaccinated people died, but 35 percent of swine flu patients who died had not been vaccinated against seasonal flu, they found.
"Seasonal vaccination might protect against the most severe forms of the disease," the researchers wrote.
Menno de Jong of the University of Amsterdam and Rogier Sanders of Cornell University in New York said the study shows some protection but said what the world really needs is a universal flu vaccine that protects people against all strains.
Currently, the seasonal vaccine must be formulated every year because influenza viruses mutate, and new strains, such as the H1N1 swine flu, require a completely new vaccine.
The new H1N1 vaccine took five months to formulate and manufacture.