Session: 278. Vaccines: Influenza, Saturday, 12:15-1:30 p.m.
Background : During 2017–18, influenza vaccine effectiveness (VE) against A(H3N2) illness was highest among children <5 years compared to all other ages. A child’s first influenza infection can shape later immune responses. The emergence of antigenically distinct influenza A(H3N2) viruses in 2014–15 provided an opportunity to explore potential effects of first virus infection on vaccine effects. We compared VE against influenza A(H3N2) during 2016–17 and 2017–18 among children born after and before 2014.
Methods : Outpatient children aged 6 months–17 years with acute respiratory illness with cough were enrolled in the United States Influenza VE Network and tested for influenza infection by RT-PCR. Vaccination status was derived through medical records and immunization registries. Children with partial or unknown vaccination status were excluded. We used a test-negative design to estimate VE and 95% confidence intervals (CI) from logistic regression, adjusting for potential confounders. Cohorts were defined by birth after or before June 2014; we assumed exposure to the new A(H3N2) virus among children born after June 2014.
Results : During 2016–17, among 2,545 children, 445 (18%) tested positive for A(H3N2) and 1,809 (71%) tested negative. VE against A(H3N2) did not differ among children born after June 2014 and among those born before June 2014 [49% (95% CI: -12%, 77%) vs. 43% (27%, 55%); interaction P <0.75]. During 2017–18, among 2,936 patients, 631 (22%) tested positive for A(H3N2), and 1,852 (63%) tested negative. VE against A(H3N2) was 59% (36%, 74%) among children born after June 2014 versus 20% (-1%, 37%) among those born before June 2014 (interaction P <0.01).
Conclusion : We did not consistently see differences in VE against A(H3N2) between children potentially exposed to different A(H3N2) viruses. However, error in exposure assignment to A(H3N2) viruses and few seasons since the emergence of the new A(H3N2) viruses limit our interpretation. Future study will include additional A(H3N2) seasons as initial exposures to current circulating viruses increase among young children. Alternative explanations for age-related differences will also be explored, such as prior seasonal vaccination.
Chandresh Ladva– Epidemic Intelligence Service Officer, Centers for Disease Control and Prevention, Atlanta, GA
Edward Belongia– Director, Center for Clinical Epidemiology & Population Health, Marshfield Clinic Research Institute, Marshfield, WI
Arnold Monto– Professor of Epidemiology, Global Public Health; Thomas Francis, Jr. Collegiate Professor of Public Health, University of Michigan, Ann Arbor, MI
Emily Martin– Assistant Professor of Epidemiology, University of Michigan, Ann Arbor, MI
Manjusha Gaglani– Josephine Ballard Endowed Chair and Professor of Pediatrics, Texas A&M University HSC COM, Temple, TX
Michael Reis– Chief Medical Officer, Baylor Scott and White Health, Dallas, TX
Michael Jackson– Associate Scientific Investigator, Kaiser Permanente Washington, Seattle, WA
Lisa Jackson– Senior Investigator, Kaiser Permanente Washington Health Research Institute, Seattle, WA
Richard Zimmerman– Investigator, University of Pittsburgh, Pittsburgh, PA
Mary Patricia Nowalk– Investigator, University of Pittsburgh, Pittsburgh, PA
Huong McLean– Research Scientist, Marshfield Clinic Research Institute, Marshfield, WI
Manish Patel– Medical Officer, Centers for Disease Control and Prevention, Atlanta, GA
Alicia Fry– Medical Epidemiologist, Centers for Disease Control and Prevention, Atlanta, GA
Brendan Flannery– US Flu VE Network PI at CDC, Centers for Disease Control and Prevention, Atlanta, GA