The vaccine against swine flu seems to offer broader protection against other flu viruses, compared with the seasonal flu vaccine, researchers say.

This vaccine, officially called the 2009 H1N1 vaccine, was administered in 2009 to protect against a new virus strain that caused a pandemic that year.

In the new study, people who received this vaccine developed antibodies against not only H1N1, but also several other flu strains, the researchers said. Such protection against multiple strains is rarely seen in people who receive the seasonal flu vaccine or are infected with seasonal flu, the researchers said.

The findings bring researchers closer to developing a universal flu vaccine — one that provides broad protection against flu viruses and lasts for years, said study researcher Rafi Ahmed, director of the Emory University’s Vaccine Center. Currently, a new seasonal flu vaccine must be developed and administered every year because its protection is limited to certain strains, and wanes over time.

The study will be published this week in the journal Proceedings of the National Academy of Sciences.

Broad protection

Previously, Ahmed and colleagues found that people who became sick with the 2009 H1N1 flu virus produced antibodies against multiple flu viruses, but it was not known whether the vaccine could do this as well.

The new study involved 24 healthy adults who were immunized with the 2009 H1N1 vaccine. Seven days after they received the flu shot, the researchers analyzed their blood.

Participants had increases in antibodies against several flu strains, including H1N1, H5N1 and H3N2. Antibodies are immune system proteins that bind to harmful pathogens, such as viruses.

A universal vaccine for flu?

Flu viruses consist of a “head” region that changes over time and varies between strains, and a “stalk” region that remains fairly constant. Usually, antibodies against the flu bind to the head of the virus, and for this reason, the protection that seasonal flu vaccines offer is typically quite specific.

However, in the new study, participants produced some antibodies that could bind to the stalk of the flu virus — it’s these antibodies that could be the basis for a universal flu vaccine, Ahmed said.

Antibodies are produced by cells called B cells. The researchers speculate that, because H1N1 was such a “new” strain of flu, it forced the body to activate a rare type of B cell, one that could produce antibodies that bind to the virus’ stalk.

“The next step now is to design a vaccine to target these B cells,” Ahmed said.

“The study is encouraging, that we’re seeing antibodies generated against the conserved portions of the virus,” said Dr. Bruce Lee, an associate professor at the University of Pittsburgh Graduate School of Public Health. “But it’s just an initial step,” Lee said, noting that much more work is needed before the results could be translated to a universal flu vaccine.

And while the production of antibodies against a virus suggests that people will be protected against it, it remains unclear whether they could avoid catching the disease, Lee said.

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