Summary of the NACI Statement on Seasonal Influenza Vaccine for 2017-2018

Demonstrating the capacity of the National Advisory Committee on Immunization for timely responses to post-market vaccine monitoring signals: Canada's experience with the live-attenuated influenza vaccine

Over the last several years, the recommended use of the live-attenuated influenza vaccine (LAIV) for children has evolved in the United States (US) in response to evidence of a potential decrease in LAIV effectiveness based on post-market monitoring. These issues were not observed in Canada or elsewhere; consequently, recommendations from Canada's National Advisory Committee on Immunization (NACI) and the US Advisory Committee on Immunization Practices (ACIP) on whether to use LAIV differed for two influenza seasons (2016-2017 and 2017-2018). This retrospective describes how NACI arrived at its recommendations in response to post-market signals of reduced LAIV performance from the US in 2013-2014 and again in 2015-2016. NACI's experience with LAIV marks the first time in Canada where a preferential recommendation on the use of an influenza vaccine in a routine immunization program was reversed. This experience highlights the importance of ongoing post-market monitoring of vaccines, international collaboration and careful consideration of local context to inform vaccine recommendations. NACI's capacity for timely responses to post-market vaccine performance signals will facilitate responsiveness to similar post-market monitoring signals from the coronavirus disease 2019 (COVID-19) vaccines.

Clinical and Economic Outcomes Associated with Cell-Based Quadrivalent Influenza Vaccine vs. Standard-Dose Egg-Based Quadrivalent Influenza Vaccines during the 2018-19 Influenza Season in the United States

Non-egg-based influenza vaccines eliminate the potential for egg-adapted mutations and potentially increase vaccine effectiveness. This retrospective study compared hospitalizations/emergency room (ER) visits and all-cause annualized healthcare costs among subjects aged 4–64 years who received cell-based quadrivalent (QIVc) or standard-dose egg-based quadrivalent (QIVe-SD) influenza vaccine during the 2018–19 influenza season. Administrative claims data (IQVIA PharMetrics^® Plus, IQVIA, USA) were utilized to evaluate clinical and economic outcomes. Adjusted relative vaccine effectiveness (rVE) of QIVc vs. QIVe-SD among overall cohort, as well as for three subgroups (age 4–17 years, age 18–64 years, and high-risk) was evaluated using inverse probability of treatment weighting (IPTW) and Poisson regression models. Generalized estimating equation models among the propensity score matched sample were used to estimate annualized all-cause costs. A total of 669,030 recipients of QIVc and 3,062,797 of QIVe-SD were identified after IPTW adjustments. Among the overall cohort, QIVc had higher adjusted rVEs against hospitalizations/ER visits related to influenza, all-cause hospitalizations, and hospitalizations/ER visits associated with any respiratory event compared to QIVe-SD. The adjusted annualized all-cause total costs were higher for QIVe-SD compared to QIVc ((+$461); p < 0.05).

Viral Shedding in Recipients of Live Attenuated Influenza Vaccine in the 2016-2017 and 2017-2018 Influenza Seasons in the United Kingdom

Background

The (H1N1)pdm09 live attenuated influenza vaccine (LAIV) strain was changed for the 2017–2018 influenza season to improve viral fitness, following poor protection against (H1N1)pdm09 viruses in 2015–2016. We conducted LAIV virus shedding studies to assess the effect of this change.

Methods

Children aged 2–18 years were recruited to receive LAIV in the 2016–2017 (n = 641) and 2017–2018 (n = 362) influenza seasons. Viruses from nasal swabs taken 1, 3, and 6 days postvaccination were quantified by reverse-transcription polymerase chain reaction and area under the curve titers were determined. Presence and quantity of shedding were compared between strains and seasons with adjustment for age and prior LAIV (n = 436), inactivated seasonal vaccine (n = 100), or (H1N1)pdm09 vaccine (n = 166) receipt.

Results

(H1N1)pdm09 detection (positivity) in 2016–2017 and 2017–2018 (11.2% and 3.9%, respectively) was lower than that of H3N2 (19.7% and 18.7%, respectively) and B/Victoria (28.9% and 33.9%, respectively). (H1N1)pdm09 positivity was higher in 2016–2017 than 2017–2018 (P = .005), but within shedding-positive participants, the (H1N1)pdm09 titer increased in 2017–2018 (P = .02). H3N2 and influenza B titers were similar between seasons. Positivity declined with age, and prior vaccination reduced the likelihood of shedding influenza B but not (H1N1)pdm09.

Conclusions

The (H1N1)pdm09 titer increased in 2017–2018, indicating more efficient virus replication in shedding-positive children than the 2016–2017 strain, although overall positivity was reduced. Age and vaccination history require consideration when correlating virus shedding and protection.

Clinical Trials Registration

NCT02143882, NCT02866942, and NCT03104790.

Risk conditions in children hospitalized with influenza in Norway, 2017-2019

BACKGROUND

Norwegian children are more frequently hospitalized with influenza than adults. Little is known about the characteristics of these children. Our aim was to investigate the presence of pre-existing risk conditions and to determine the duration of influenza hospitalizations in children during two influenza seasons.

METHODS

The Norwegian Patient Registry holds data on all hospitalized patients in Norway. We included all patients younger than 18 years hospitalized with a diagnosis of influenza during the influenza seasons 2017-18 and 2018-19. Pre-existing risk conditions for influenza were identified by ICD-10 diagnoses in the Norwegian Patient Registry. In addition, information on asthma diagnoses were also retrieved from the Norwegian Registry for Primary Health Care. To estimate the prevalence of risk conditions in the child population, we obtained diagnoses on all Norwegian children in a two-year period prior to each influenza season. We calculated age-specific rates for hospitalization and risk for being hospitalized with influenza in children with risk conditions.

RESULTS

In total, 1013 children were hospitalized with influenza during the two influenza seasons. Children younger than 6 months had the highest rate of hospitalization, accounting for 13.5% of all admissions (137 children). Hospitalization rates decreased with increasing age. Among children hospitalized with influenza, 25% had one or more pre-existing risk conditions for severe influenza, compared to 5% in the general population under 18 years. Having one or more risk conditions significantly increased the risk of hospitalization, (Odds Ratio (OR) 6.1, 95% confidence interval (CI) 5.0-7.4 in the 2017-18 season, and OR 6.8, 95% CI 5.4-8.4 in the 2018-19 season). Immunocompromised children and children with epilepsy had the highest risk of hospitalization with influenza, followed by children with heart disease and lung disease. The average length of stay in hospital were 4.6 days, and this did not differ with age.

CONCLUSION

Children with pre-existing risk conditions for influenza had a higher risk of hospitalization for influenza. However, most children (75%) admitted to hospital with influenza in Norway during 2017-2019 did not have pre-existing risk conditions. Influenza vaccination should be promoted in particular for children with risk conditions and pregnant women to protect new-borns.

A real-world study evaluating the relative vaccine effectiveness of a cell-based quadrivalent influenza vaccine compared to egg-based quadrivalent influenza vaccine in the US during the 2017-18 influenza season

BACKGROUND

Cell-based influenza vaccine manufacturing reduces egg adaptations that can decrease vaccine effectiveness. We evaluated the relative vaccine effectiveness (rVE) of cell-based quadrivalent influenza vaccine (QIVc) compared to standard-dose egg-based quadrivalent influenza vaccines (QIVe-SD) against influenza-related and serious respiratory events among subjects 4-64 years of age during the 2017-18 influenza season.

METHODS

A retrospective cohort analysis was conducted using administrative claims data in the US (IQVIA PharMetrics Plus® database). Subjects vaccinated with QIVc or QIVe-SD from 8/2017-1/2018 were identified (date of vaccination termed the index date). Influenza-related hospitalizations/ER visits, all-cause hospitalizations and serious respiratory hospitalizations/ER visits were assessed post-vaccination. Inverse probability of treatment weighting (IPTW) and Poisson regression were used to evaluate the adjusted rVE of QIVc compared to QIVe-SD. In a subgroup analysis, rVE was assessed for several subgroups of interest (4-17, 18-64 and 50-64 years, and subjects with ≥1 high-risk condition). In a secondary economic analysis, annualized all-cause costs over the follow-up were compared using propensity score matching (PSM) and generalized estimating equation (GEE) models.

RESULTS

The study sample comprised 555,538 QIVc recipients and 2,528,524 QIVe-SD recipients. Prior to adjustment, QIVc subjects were older and had higher total costs in the 6-months pre-index. Following IPTW-adjustment and Poisson regression, QIVc was more effective in reducing influenza-related hospitalizations/ER visits, all-cause hospitalizations, and hospitalizations/ER visits related to asthma/COPD/bronchial events and other respiratory events compared to QIVe-SD. Similar trends were generally observed in the subgroup analysis. Following PSM adjustment and GEE regression, QIVe-SD was associated with significantly higher annualized all-cause total costs compared to QIVc, driven by higher costs for outpatient medical services and inpatient hospitalizations.

CONCLUSIONS

After adjustment for confounders and selection bias, QIVc reduced influenza-related hospitalizations/ER visits, all-cause hospitalizations, and serious respiratory hospitalizations/ER visits compared to QIVe-SD. QIVc was associated with significantly lower all-cause total costs.

Effectiveness of Live Attenuated vs Inactivated Influenza Vaccines in Children During the 2012-2013 Through 2015-2016 Influenza Seasons in Alberta, Canada: A Canadian Immunization Research Network (CIRN) Study

IMPORTANCE

Recent observational studies report conflicting results regarding the effectiveness of live attenuated influenza vaccine (LAIV), particularly against influenza A(H1N1)pdm09.

OBJECTIVE

To compare the effectiveness of LAIV and inactivated influenza vaccine (IIV) against laboratory-confirmed influenza.

DESIGN, SETTING, AND PARTICIPANTS

A test-negative study to estimate influenza vaccine effectiveness (VE) using population-based, linked, individual-level laboratory, health administrative, and immunization data. Data were obtained from 10 169 children and adolescents aged 2 to 17 years (children) who were tested for influenza in inpatient or outpatient settings during periods when influenza was circulating based on a threshold level of 5% weekly test positivity for the province during the 4 influenza seasons spanning from November 11, 2012, to April 30, 2016, in Alberta, Canada. Logistic regression was used to estimate VE by vaccine type, influenza season, and influenza type and subtype. The relative effectiveness of each vaccine type was assessed by comparing the odds of laboratory-confirmed influenza infection for LAIV recipients with that for IIV recipients.

EXPOSURES

The primary exposure was receipt of LAIV or IIV before testing for influenza.

MAIN OUTCOMES AND MEASURES

The primary outcome was influenza case status as determined by reverse-transcriptase polymerase chain reaction testing.

RESULTS

A total of 10 779 respiratory specimens (from 10 169 children) collected and tested for influenza during the 4 influenza seasons were included, with 53.4% from males; the mean (SD) age was 7.0 (4.6) years. Across the 4 influenza seasons, 3161 children tested positive for influenza. Combining the 4 influenza seasons, the adjusted VE against influenza A(H1N1)pdm09 was 69% (95% CI, 56%-78%) for LAIV compared with 79% (95% CI, 70%-86%) for IIV. Vaccine effectiveness against influenza A(H3N2) was 36% (95% CI, 14%-53%) for LAIV and 43% (95% CI, 22%-59%) for IIV. Against influenza B, VE was 74% (95% CI, 62%-82%) for LAIV and 56% (95% CI, 41%-66%) for IIV. There were no significant differences in the odds of influenza infection for LAIV recipients compared with IIV recipients except for influenza B during the 2015-2016 season, when LAIV recipients had lower odds of infection than IIV recipients (odds ratio, 0.36; 95% CI, 0.17-0.76).

CONCLUSIONS AND RELEVANCE

There was no evidence to support the lack of effectiveness of LAIV against influenza A(H1N1)pdm09. These results support administration of either vaccine type in this age group.

Intranasal influenza vaccine: Why does Canada have different recommendations from the USA on its use?

Canada and the USA differ in their recommendations for the use of live attenuated influenza vaccine (LAIV). The Canadian National Advisory Committee on Immunization (NACI) continues to recommend LAIV as one of the influenza vaccines available for use in children 2 to 17 years of age. The US Advisory Committee on Immunization Practices (ACIP) made an interim recommendation against the use of LAIV for the 2016 to 2017 influenza season in response to low LAIV effectiveness observed in the USA during the 2013 to 2014 to 2015 to 2016 seasons. The recommendation has been continued for the 2017 to 2018 season. In response, NACI undertook a review of available LAIV effectiveness data in children and adolescents from Canada, the USA and a number of European countries. This commentary by Canada's Chief Public Health Officer summarizes the findings of that review and provides the rationale for Canada's current continued recommendation for LAIV use.