How Long Can the Flu Vaccine Be Effective?

New research finds that the influenza vaccine can protect for 6 months and last throughout flu season, while another study suggests that pediatric flu vaccination was directly linked to reduced hospitalizations among children.

The first study, led by Jennifer Radin, PhD, MPH, an epidemiologist at the Naval Health Research Center in San Diego, Calif., collected and evaluated outpatient data from 4 flu seasons, from the years 2010/2011 to 2013/2014. Radin and colleagues found that protection was consistent for 91 to 180 days after vaccination among 60% of 1,720 participants. (Among those taking part in the study, 75% were younger than 25 years old, and 55% were female. Complete data were available for 1,522 participants.) After 180 days, however, the effectiveness of the vaccine decreased to less than 11%, notes Radin.
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“Our study found moderate, sustained protection up to 6 months post-vaccination, which is the duration of most influenza seasons, says Radin, who presented the findings at the International Conference on Emerging Infectious Diseases (ICEID), held August 24 - 26 in Atlanta, Ga.

Consequently, administering influenza vaccines early in the fall, before influenza begins circulating, “may still prevent the great number of infections,” she says, adding that “we also saw a marked decline in protection after 6 months, suggesting the importance of yearly flu vaccination.”

The second study, also presented at ICEID, evaluated the immunization of children, obtaining data on annual vaccination rates from the National Immunization Survey and the Behavioral Risk Factor Surveillance System.

Led by Cecile Viboud, PhD, from the division of epidemiology and population studies at the National Institutes of Health, the authors found a direct association between pediatric flu vaccination and fewer hospitalizations in children, and—albeit indirectly and to a lesser extent—affected adults.

Among participants aged 19 and younger, vaccination significantly reduced hospitalization for pneumonia, influenza, and respiratory and circulatory diseases. While noting that the trend was less consistent among adults studied, Viboud reported that influenza-related hospitalizations also declined among adults age 20 to 49.

These findings, she says, suggest that “the childhood influenza immunization program is effective in reducing the severe burden of influenza among children and, hence, the vaccination of this age group should be promoted.”

And, while describing the recent decline in adult hospitalization rates “intriguing,” Viboud notes that further research “should evaluate whether this is due to herd immunity, declining influenza activity, or unrelated long-term time trends.”

—Mark McGraw

Reference:

Little effect of varying specimen storage temperature on influenza PCR results. Study Presented at: International Conference on Emerging Infectious Diseases (ICEID). August 24, 2015.