May 21, 2014
Despite Lower Vaccine Effectiveness, Older Adults Significantly Benefit From Flu Jab

Atlanta—Even in seasons with lower vaccine effectiveness, vaccination against influenza still significantly reduces hospitalization in adults 65 years old and older, according to a new study from the CDC.

The study, published online recently by Clinical Infectious Diseases, bolsters the CDC’s recommendation for annual vaccination of adults 65 years and older, especially those who are at high risk for serious flu-related complications. Older adults, in general, have more risk for serious flu complications and death, the report notes.

For the study, researchers used statistical modeling to estimate flu vaccine–prevented hospitalizations in adults aged 65 years and older, taking into consideration estimates of vaccine effectiveness against medically attended influenza illness ranging from 10% to 70%. Data used was collected during flu seasons in 2011-12, considered to be mild, and 2012-13, categorized as moderate to severe.

Results indicated that during the more severe 2012-13 flu season, a flu vaccine with 10% effectiveness (and 66% coverage) would avert about 13,000 hospitalizations. A vaccine with 40% effectiveness, meanwhile, would avert about 60,000 hospitalizations.

During the milder 2011-12 season, however, a flu vaccine with the same effectiveness estimates as the two examples above would avert about 2,000 and 11,000 hospitalizations, respectively.

Overall vaccine effectiveness against medically attended influenza illness across all age groups was estimated at 47% in 2011-12 and 52% in unpublished data for 2012-2013. Effectiveness dropped considerably in the older age group—65 and older—to 43% in 2011-12 and 32% in unpublished estimates for 2012-2013.

Presenting the findings in a different way, the researchers also estimated how many people would need to be vaccinated to prevent one hospitalization. For the 2012-13 season, 476 people would have needed to be vaccinated to prevent one hospitalization, assuming vaccine effectiveness was 40%. The number was much higher for the milder 2011-12 season in which fewer hospitalizations occurred in general; 2,457 people would have needed to be vaccinated to prevent one hospitalization in that flu season.

Despite greater benefit against hospitalization during moderate-to-severe seasons compared with milder seasons, the study emphasizes that flu vaccination substantially reduces morbidity and mortality at any time.

“We show that influenza vaccination would be expected to prevent a substantial number of hospitalizations in older adults in the United States for all hypothetical vaccine effectiveness estimates, during both mild and moderate to severe seasons, and that even modest improvements in vaccine effectiveness could result in substantial reductions in the number of hospitalizations,” the authors write.

The researchers also call for more use of high-dose vaccines in older adults, pointing out, “While immunogenicity may not correspond directly to increased protections against illness, higher post-vaccination antibody levels have been demonstrated in older adults for both adjuvanted and high-dose inactivated influenza vaccines compared to standard dose inactivated vaccines.”

U.S. Pharmacist Social Connect