The flu vaccine may help prevent flu-related pneumonia, a study suggests.

When researchers looked at patients with pneumonia, those whose pneumonia was related to the flu were more likely to have skipped the flu vaccine, compared to patients with pneumonia from other causes.

Pneumonia can be a serious and common complication of catching the flu, the authors write.

"We knew that influenza vaccines could prevent fever and respiratory symptoms associated with influenza infections, but whether influenza vaccines could prevent pneumonia - a more serious complication of influenza infection - was unclear," said lead author Dr. Carlos G. Grijalva of the Vanderbilt University School of Medicine in Nashville, Tennessee.

As reported in JAMA, the researchers used data on 2,767 children and adults hospitalized for pneumonia between 2010 and 2012 - including 162 who had laboratory-confirmed influenza.

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Of the 162 people with influenza-associated pneumonia, only 28, or 17 percent, had been vaccinated. Almost 30 percent of the comparison cases had been vaccinated.

Patients whose pneumonia wasn't associated with flu were almost twice as likely to have been vaccinated, the researchers found.

"We know from other studies that influenza vaccines reduce the risk of influenza disease by about 50 percent," said Michael L. Jackson, an infectious disease epidemiologist at Cornell University who was not part of the new study.

"We would expect that the vaccine would prevent severe complications of influenza (such as pneumonia) by approximately that same amount; people who don't get the flu because of the vaccine also would not get pneumonia," he said.

Some people do not get the vaccine because they do not believe the flu is a serious disease, while others have logistical challenges getting the shot every year, Jackson told Reuters Health by email.

"Influenza pneumonia affects more intensely both young children and older adults," Grijalva said.

This study did not compare the outcomes of flu-associated pneumonia with other cases of pneumonia, but all were serious and required hospitalization, he said.

There are different influenza vaccines available, which don't all have the same effectiveness - higher-dose flu vaccines have been recommended for older adults and have been more effective than the standard dose, Grijalva said.

Flu is not the only cause of pneumonia, he noted.

"Effective vaccines against bacteria that can also cause pneumonia are available and currently recommended for use," he told Reuters Health by email. "For example, pneumococcal and Haemophilus influenzae vaccines are already recommended for prevention of infections caused by these bacteria."

Now is a good time to get the flu vaccine, especially as researchers continue to learn more about its benefits, he said.