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2732. Estimate of the Effectiveness of Influenza Vaccine among Children for the 2017–2018 Season

Abstract Background The 2017–2018 influenza season was one of the deadliest in decades, with 180 pediatric deaths, 80% among children who did not receive the vaccine. Circulating influenza strains change periodically, making it important to determine vaccine efficacy on an annual basis specifically in susceptible populations. The primary aim of our study was to estimate the effectiveness of the influenza vaccine for the 2017–2018 season. Secondary aims were to determine effect of weaning immunity and of previous season vaccination. Methods Children 6 months to 17 years tested for influenza during the 2017–2018 season at Children’s Hospital of New Orleans were included. Clinical charts were reviewed, and immunization status confirmed via the Louisiana Immunization Registry. Using a multivariable logistic regression model vaccine effectiveness (VE) was estimated by comparing vaccination status of influenza-positive vs. influenza-negative cases with the formula VE = (1 − OR) × 100%. Results 4,825 children were included; 22% of them tested positive for influenza, mostly influenza A (61.9%); 21% had received an influenza vaccine prior to illness: 14% among the influenza-positive and 23% among influenza-negative (P < 0.0001). Overall, VE for the 2017–2018 influenza season was 43% (95% CI 30, 53); 44% for influenza A and 38% for influenza B. While receiving current year (2017–2018) vaccine had the most effect, receiving the previous year (2016–2017) vaccine had additional benefit. We found no waning immunity of the vaccine for the 2017–2018 season. Conclusion Influenza VE was modest for children in the local area of New Orleans and similar to the CDC’s findings for the nation as a whole. Previous year vaccination had a small, but significant benefit and there was no evidence of waning immunity in our cohort. Ongoing national and local surveillance is important to understand the benefit of influenza vaccination. Disclosures All authors: No reported disclosures.


Background:
We evaluated influenza VE over two consecutive years vs. the current season against influenza illness during two H3N2-predominant seasons in children receiving care at emergency/urgent care (ED/UC) facilities in metropolitan Colorado.
Methods : We conducted a test-negative case-control analysis of 1478 children aged 6 months to 8 years enrolled at Children's Hospital Colorado ED/UC with influenza like illness during the 2016-2017 and 2017-2018 influenza seasons. The primary outcome was PCR-confirmed influenza and vaccination status was confirmed using electronic medical record and parental interviews. Vaccination status was defined as completely vaccinated (all doses of influenza vaccine according to child's age); partially or not vaccinated children were defined as unvaccinated. Multivariable logistic regression models adjusted for high-risk medical condition, age, race and insurance status were used to calculate odds ratios (OR) and 95% confidence intervals. Vaccine effectiveness was calculated as (1 − OR) × 100.
Results: Of the 1224 (82.8%) children enrolled in the study with known vaccination status for both seasons, 361 (29%) tested positive for influenza. Overall, VE against influenza was 49% (95% CI, 33-61%) after adjusting for other covariates in the model. VE did not differ significantly between those vaccinated in both seasons and those vaccinated in only the current season (VE 69%, 95% CI 41-115) ( Table 1).
Conclusion: Our estimates of influenza VE for two predominantly H3N2-influenza seasons in Colorado are comparable to the CDC -VE for children 6 months to 8 years. VE against ED or UC-attended influenza illness in children did not vary significantly by prior seasons' vaccination status.
Disclosures. All authors: No reported disclosures. The 2017-2018 influenza season was one of the deadliest in decades, with 180 pediatric deaths, 80% among children who did not receive the vaccine. Circulating influenza strains change periodically, making it important to determine vaccine efficacy on an annual basis specifically in susceptible populations. The primary aim of our study was to estimate the effectiveness of the influenza vaccine for the 2017-2018 season. Secondary aims were to determine effect of weaning immunity and of previous season vaccination.

Estimate of the Effectiveness of Influenza
Methods: Children 6 months to 17 years tested for influenza during the 2017-2018 season at Children's Hospital of New Orleans were included. Clinical charts were reviewed, and immunization status confirmed via the Louisiana Immunization Registry. Using a multivariable logistic regression model vaccine effectiveness (VE) was estimated by comparing vaccination status of influenza-positive vs. influenza-negative cases with the formula VE = (1 − OR) × 100%.
Results: 4,825 children were included; 22% of them tested positive for influenza, mostly influenza A (61.9%); 21% had received an influenza vaccine prior to illness: 14% among the influenza-positive and 23% among influenza-negative (P < 0.0001). Overall, VE for the 2017-2018 influenza season was 43% (95% CI 30, 53); 44% for influenza A and 38% for influenza B. While receiving current year (2017-2018) vaccine had the most effect, receiving the previous year (2016-2017) vaccine had additional benefit. We found no waning immunity of the vaccine for the 2017-2018 season.
Conclusion: Influenza VE was modest for children in the local area of New Orleans and similar to the CDC's findings for the nation as a whole. Previous year vaccination had a small, but significant benefit and there was no evidence of waning immunity in our cohort. Ongoing national and local surveillance is important to understand the benefit of influenza vaccination.
Disclosures. All authors: No reported disclosures.