Flu Vaccination Study Confirms Programs’ Efficacy

Vaccination against influenza substantially reduces the disease’s burden in the United States each year, according to the results of a unique look at the impact of vaccinations.

The United States is the only country with universal influenza vaccine recommendations that suggest everyone aged 6 months and older receive an annual dose of the vaccine. However, previous studies have not provided a reliable assessment of the number of flu cases or hospitalizations that are prevented by vaccination each year.

A new CDC study confirmed the value of the nation’s influenza vaccination program. CDC influenza experts used a new method to measure the impact of the US flu vaccination program from 2005 to 2011 by modeling the number of illnesses, medically attended illnesses, and hospitalizations averted by flu vaccination.

“This study demonstrates that the vaccination program averts influenza-related illnesses and hospitalizations on a large scale,” Lyn Finelli, DrPH, MS, Lead, Influenza Surveillance and Outbreak Response Team, Epidemiology and Prevention Branch, Influenza Division at the CDC, told ConsultantLive.

“This study estimated that cumulatively over 6 influenza seasons, from 2005 to 2011, influenza vaccination averted about 13.6 million illnesses, 5.8 million medical visits, and approximately 112,900 influenza-related hospitalizations in the United States,” she said.

The study highlighted the need for more persons to get vaccinated, Dr Finelli noted. “The higher the coverage, the more influenza cases, patient visits, and hospitalizations that can be averted,” she said.

The highest fraction of potential influenza cases prevented was observed during the most recent season of the study period, 2010-2011, when more than 18% of potential influenza illnesses were averted by vaccination, reflecting the post-pandemic expansion of vaccination coverage.

Although the vaccine produced benefits each season, the number of influenza-associated outcomes averted by vaccination fluctuated across age groups and seasons, reflecting the interplay of seasonal differences in vaccination coverage, vaccine effectiveness, and influenza attack rate.

“Calculating the prevented disease fraction instead of the number of averted cases can be useful for describing the impact of vaccination programs because it controls for the relative severity of different seasons,” the authors wrote. “The prevented fraction can also present a different pattern of impact over time than the number of averted outcomes alone-a pattern which more clearly reflects the benefits of increased vaccination coverage. The population-level benefits of increased vaccination become apparent when comparing the generally rising trend in vaccination coverage over time to the trend in the prevented fraction over time for each age group.”

There is a need for vaccines with greater efficacy, especially in older patients, Dr Finelli noted. “Vaccine effectiveness for the elderly is only moderate,” she said. “The higher the vaccine effectiveness, the more cases averted in this age group.”

Primary care physicians need to make sure their at-risk patients are vaccinated, according to Dr Finelli. “Use every opportunity to vaccinate at all follow-up visits and sick visits from September to February,” she said, noting that most high-risk patients come to the doctor at least once during that time.

“Influenza vaccination is the best method to prevent influenza and its complications,” Dr Finelli concluded. “The more we vaccinate, the more illnesses and hospitalizations we prevent.”

The researchers published their results in June 19, 2013 PLoS One.