Flu Shot May Reduce Pneumonia Risk

Those who received the flu vaccine were 59% less likely to be hospitalized for pneumonia, a new study finds.

Children and adults who are vaccinated against influenza are not only at decreased risk for flu, they are also less likely to develop flu-associated pneumonia, new research suggests.

Although the Centers for Disease Control and Prevention (CDC) estimates that the flu shot reduces the risk of influenza infection by about 60%, some adults and children who receive the vaccination will still be infected each season. However, the study, presented on October 3, 2013, at ID Week in San Francisco, suggests that those who are vaccinated are less likely to develop serious flu-related complications.

The study evaluated the effectiveness of the influenza vaccine in preventing community-acquired pneumonia, one of the most severe complications of flu. Using data from the CDC’s prospective Etiology of Pneumonia in the Community (EPIC) study, the researchers assessed the rates of influenza vaccination in cases of influenza-related community-acquired pneumonia and in pneumonia cases unrelated to flu during the 2009-2010, 2010-2011, and 2011-2012 flu seasons. The EPIC study enrolled children and adults hospitalized with pneumonia in Memphis, Nashville, Chicago, and Salt Lake City. Influenza cases were lab-confirmed though nose and throat swabs, and self-reports on vaccination history were confirmed through medical records.

A total of 1524 patients admitted for pneumonia were included in the study, and 126 of those were diagnosed with both influenza and pneumonia. Among patients with influenza-related pneumonia, only 22% had been vaccinated, compared with 35% of influenza-negative pneumonia patients. Overall, the vaccine was estimated to be 59% effective in preventing pneumonia hospitalizations. In subgroup analyses, the vaccine was significantly more effective in preventing pneumonia among children than among adults. Flu vaccination was associated with a 79% decreased risk for pneumonia among children younger than 18 years of age and with a 36% reduced risk among adults. Despite this variation among age groups, overall vaccine effectiveness did not vary significantly after adjusting for demographics, high risk-conditions, season, site, and time from disease onset.

Vaccination verification through medical records was not possible for all patients, and the results may have been affected by other variables not accounted for, the researchers note. However, the study’s results are stronger than those from previous research that focused on all-cause pneumonia, lacked laboratory confirmation for influenza cases, or lacked vaccine verification. Despite the limitations of the study, the researchers say that the preliminary results indicate that individuals, especially children, who get a flu shot are at decreased risk for being hospitalized with pneumonia during flu season.