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2014-2015 Influenza Vaccine Effectiveness in the United States by Vaccine Type
Richard K Zimmerman1, Mary Patricia Nowalk1, Jessie Chung2
1University of Pittsburgh, Pennsylvania.
Insights
The 2014-2015 influenza vaccines showed limited effectiveness against A/H3N2 but were effective against influenza B. Live attenuated influenza vaccine (LAIV) was not recommended for children aged 2-8 years.
Area of Science:
- Virology
- Immunology
- Public Health
Background:
- Influenza A/H3N2 viruses significantly drifted after the selection of strains for the 2014-2015 vaccines.
- The Advisory Committee on Immunization Practices recommended live attenuated influenza vaccine (LAIV) over inactivated influenza vaccine (IIV) for children aged 2-8 years during the 2014-2015 season.
Purpose of the Study:
- To evaluate the vaccine effectiveness (VE) of the 2014-2015 influenza vaccines against circulating influenza A/H3N2 and influenza B/Yamagata strains.
- To compare the VE of IIV and LAIV in children aged 2-8 years.
Main Methods:
- A test-negative design study was conducted among outpatients with acute respiratory illness at 5 US sites.
- Vaccination status was compared between reverse transcription polymerase chain reaction-confirmed influenza positive and negative cases.
Main Results:
- Overall adjusted VE was 19%, but it was not statistically significant in the 18-64 age group.
- VE against A/H3N2 was low (6%) and not statistically significant, while VE against influenza B/Yamagata was high (55%).
- In children aged 2-8 years, VE against A/H3N2 was 15% for IIV and -3% for LAIV. VE against B/Yamagata was 40% for IIV and 74% for LAIV.
Conclusions:
- The 2014-2015 influenza vaccines provided minimal protection against A/H3N2 but were effective against influenza B.
- The preferential recommendation for LAIV in young children was not supported by the study findings.
Background:
Circulating A/H3N2 influenza viruses drifted significantly after strain selection for the 2014-2015 vaccines. Also in 2014-2015, the Advisory Committee on Immunization Practices recommended preferential use of live attenuated influenza vaccine (LAIV) over inactivated influenza vaccine (IIV) among children aged 2-8 years.
Methods:
Vaccine effectiveness (VE) across age groups and vaccine types was examined among outpatients with acute respiratory illness at 5 US sites using a test-negative design, that compared the odds of vaccination among reverse transcription polymerase chain reaction-confirmed influenza positives and negatives.
Results:
Of 9311 enrollees with complete data, 7078 (76%) were influenza negative, 1840 (19.8%) were positive for influenza A (A/H3N2, n = 1817), and 395 (4.2%) were positive for influenza B (B/Yamagata, n = 340). The overall adjusted VE was 19% (95% confidence interval [CI], 10% to 27%) and was statistically significant in all age strata except those aged 18-64 years. The adjusted VE of 6% (95%CI, -5% to 17%) against A/H3N2-associated illness was not statistically significant, unlike VE for influenza B/Yamagata, which was 55% (95%CI, 43% to 65%). Among those aged 2-8 years, VE against A/H3N2 was 15% (95%CI, -16% to 38%) for IIV and -3% (CI, -50% to 29%) for LAIV; VE against B/Yamagata was 40% (95%CI, -20% to 70%) for IIV and 74% (95%CI, 25% to 91%) for LAIV.
Conclusions:
The 2014-2015 influenza vaccines offered little protection against the predominant influenza A/H3N2 virus but were effective against influenza B. Preferential use of LAIV among young children was not supported.
