1. Despite removing a recommendation to use the live attenuated influenza vaccine, vaccination rates remained relatively stable in the state of Oregon.
2. Children who had previously received an inactivated influenza vaccine were slightly more likely to return the following year for another inactivated vaccine in comparison to those who had previously received the live attenuated version.
Evidence Rating Level: 2 (Good)
Study Rundown: In Oregon, a state known for high rates of vaccine hesitancy, concerns arose when the Advisory Committee on Immunization Practices withdrew its recommendation encouraging the use of the live attenuated influenza vaccine (LIAV).Researchers feared needle- and vaccine-averse families preferred the intranasal administration of the LIAV. Using vaccine data from Oregon’s ALERT Immunization Information System (ALERT IIS), researchers compared vaccination rates over the last 5 years, including the year after the withdrawal of the recommendation. Rates of LAIV versus the inactivated influenza vaccine (IIV), a needle-administered vaccine, were also tracked. Researchers discovered minimal to no changes in yearly vaccination rates across the last 5 seasons despite a shift in the proportion of patients receiving the IIV. Patients who had previously received the LAIV were slightly less likely to return for the IIV the following year when compared with a matched cohort who had received the IIV the previous year. This difference was minimal, however, in many of the age groups evaluated within the larger cohort. Though limited in its generalizability beyond states with large vaccine-hesitant populations, the study results highlight how vaccine administration is less critical in affecting vaccine rates than providers or researchers may have previously assumed.
In-Depth [retrospective cohort]: Utilizing data from Oregon’s statewide immunization registry, the ALERT Immunization Information System (IIS), which houses more than 55 million immunization records, researchers reviewed vaccine rates in children ages 2 – 17 during the last 5 influenza seasons, starting with 2012-2013 and ending with 2016-2017. Researchers then completed a matched-cohort study comparing those who received the LAIV with those who received the IIV in the 2015-2016 season, analyzing the rates of IIV administration in each population during the 2016-2017 year, after withdrawal of preferential LAIV use recommendations. Over the last five seasons, researchers discovered a vaccination stable rate, ranging from 32.6% to 35.2%, with the 2015-2016 and 2016-2017 seasons being equal at 32.6%. The matched-cohort portion of the study revealed 56.4% of children who received the IIV in the 2015-2016 season received the IIV again during the 2016-2017 season, while 53.1% of those who received the LAIV in 2015-2016 received the IIV in 2016-2017, making those who had received a previous IIV 1.05 times more likely to receive the vaccine again (95%CI 1.04 to 1.06). When 15 of the individual age groups were assessed within the larger cohort, 6 had no significant difference in IIV administration rate in 2016-2017 when children with previous IIV receipt were compared to those who had previously received LAIV.
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