How did a flu vaccine work?

In a study published online Tuesday, scientists at the University of California, Davis, have discovered how a vaccine that blocks the virus’ ability to cause a pandemic is also able to stop it from triggering a new strain of the virus that is now circulating.

This new strain is also more infectious and has more potential for causing disease than the flu itself, according to the scientists who found the result.

The study, which was published online in the journal Science, is the first to directly link a vaccine to preventing the spread of pandemic-level illness.

“This is the most significant finding we’ve made about the flu vaccine,” said lead author Jodi Zuckerman, a researcher in the UC Davis Center for Disease Control and Prevention’s Division of Infectious Diseases.

“This vaccine works, we’re seeing that it’s helping protect us against this virus, and the flu has not killed people yet.”

It’s a rare finding.

Scientists have been studying flu vaccines for years, but there has never been a study that directly linked a flu shot to preventing an outbreak.

In a 2009 study, researchers found that the flu shot is the only vaccine that can stop the spread and development of the H5N1 virus, which causes a pandemically contagious strain of influenza.

When a new pandemic arises, the H7N9 strain, which originated in the 1930s and 1940s, can evolve rapidly.

And the H8N9 virus, that has a much shorter incubation period and has been more dangerous, has been found to be more infectious than the H9N2 strain that caused the pandemic.

Scientists are still trying to figure out how to stop these viruses from forming new strains.

But a vaccine may be the best way to stop them.

The UC Davis study found that after two doses of the flu vaccines, there was a 50 percent reduction in the number of new influenza infections.

That’s because the flu virus in the vaccine is more contagious and can travel longer distances, researchers said.

Zuckerman said that researchers also found that a second dose of the vaccine did not stop the virus from multiplying in the body, meaning that it could continue to infect people even after a flu vaccination.

While vaccines are the most widely used way to prevent pandemic illness, the scientists found that some people, like pregnant women and the elderly, may be at increased risk of getting influenza after getting the second dose.

“We don’t know why, and that’s why we need to find out,” Zuckermans study author and UC Davis researcher Sarah C. Tischler, a professor of epidemiology and virology, said in a statement.

But if the new vaccine is successful in preventing a new virus, scientists hope to eventually be able to make vaccines that are more effective and safer than existing vaccines.

For now, the researchers have limited their study to the flu.

They plan to study other flu vaccines and how they interact with existing vaccines in the future.

There is one other flu vaccine currently in clinical trials that uses a modified version of the human coronavirus that caused a pandemia in 2008 and 2009.

That vaccine, called M7, is also currently in the phase II clinical trials, but researchers do not know if it will be effective in preventing future pandemics.

ABC News’ Alexia Garcia contributed to this report.