Trivalent and quadrivalent seasonal influenza vaccine in adults aged 60 and older: a systematic review and network meta-analysis

OBJECTIVES

To compare the efficacy of influenza vaccines of any valency for adults 60 years and older.

DESIGN AND SETTING

Systematic review with network meta-analysis (NMA) of randomised controlled trials (RCTs). MEDLINE, EMBASE, JBI Evidence-Based Practice (EBP) Database, PsycINFO, and Cochrane Evidence -Based Medicine database were searched from inception to 20 June 20, 2022. Two reviewers screened, abstracted, and appraised articles (Cochrane Risk of Bias (ROB) 2.0 tool) independently. We assessed certainty of findings using Confidence in Network Meta-Analysis and Grading of Recommendations, Assessment, Development and Evaluations approaches. We performed random-effects meta-analysis and network meta-analysis (NMA), and estimated odds ratios (ORs) for dichotomous outcomes and incidence rate ratios (IRRs) for count outcomes along with their corresponding 95% confidence intervals (CIs) and prediction intervals.

PARTICIPANTS

Older adults (≥60 years old) receiving an influenza vaccine licensed in Canada or the USA (vs placebo, no vaccine, or any other licensed vaccine), at any dose.

MAIN OUTCOME MEASURES

Laboratory-confirmed influenza (LCI) and influenza-like illness (ILI). Secondary outcomes were the number of vascular adverse events, hospitalisation for acute respiratory infection (ARI) and ILI, inpatient hospitalisation, emergency room (ER) visit for ILI, outpatient visit, and mortality, among others.

RESULTS

We included 41 RCTs and 15 companion reports comprising 8 vaccine types and 206 032 participants. Vaccines may prevent LCI compared with placebo, with high-dose trivalent inactivated influenza vaccine (IIV3-HD) (NMA: 9 RCTs, 52 202 participants, OR 0.23, 95% confidence interval (CI) (0.11 to 0.51), low certainty of evidence) and recombinant influenza vaccine (RIV) (OR 0.25, 95%CI (0.08 to 0.73), low certainty of evidence) among the most efficacious vaccines. Standard dose trivalent IIV3 (IIV3-SD) may prevent ILI compared with placebo, but the result was imprecise (meta-analysis: 2 RCTs, 854 participants, OR 0.39, 95%CI (0.15 to 1.02), low certainty of evidence). Any HD was associated with prevention of ILI compared with placebo (NMA: 9 RCTs, 65 658 participants, OR 0.38, 95%CI (0.15 to 0.93)). Adjuvanted quadrivalent IIV (IIV4-Adj) may be associated with the least vascular adverse events, but the results were very uncertain (NMA: eight 8 RCTs, 57 677 participants, IRR 0.18, 95%CI (0.07 to 0.43), very low certainty of evidence). RIV on all-cause mortality may be comparable to placebo (NMA: 20 RCTs, 140 577 participants, OR 1.01, 95%CI (0.23 to 4.49), low certainty of evidence).

CONCLUSIONS

This systematic review demonstrated efficacy associated with IIV3-HD and RIV vaccines in protecting older persons against LCI. RIV vaccine may reduce all-cause mortality when compared with other vaccines, but the evidence is uncertain. Differences in efficacy between influenza vaccines remain uncertain with very low to moderate certainty of evidence.

PROSPERO REGISTRATION NUMBER

CRD42020177357.

Summary of the National Advisory Committee on Immunization (NACI) Seasonal Influenza Vaccine Statement for 2023-2024

Background

The National Advisory Committee on Immunization (NACI) reviews the evolving evidence on influenza immunization and provides annual recommendations regarding the use of seasonal influenza vaccines. The NACI Statement on Seasonal Influenza Vaccine for 2023-2024 updates the 2022-2023 NACI recommendations.

Objective

To summarize the 2023-2024 NACI seasonal influenza vaccine recommendations and to highlight new and updated information.

Methods

In the preparation of the Statement on Seasonal Influenza Vaccine for 2023-2024, the NACI Influenza Working Group applied the NACI evidence-based process to critically appraise the available evidence and to propose recommendations. The recommendations were then considered and approved by NACI in light of the available evidence.

Results

Key changes for the 2023-2024 season include: 1) incorporation of updated information/guidance on influenza vaccination in the context of the coronavirus disease 2019 (COVID-19); 2) new recommendations for Flucelvax® Quad and Influvac® Tetra, the two quadrivalent inactivated influenza vaccines with expanded paediatric age indications; and 3) an update to the format of the Statement.

Conclusion

Overall, NACI continues to recommend that an age-appropriate influenza vaccine should be offered annually to all individuals aged six months and older who do not have a contraindication to the vaccine, with particular focus on the groups for whom influenza vaccination is particularly recommended.

Safety of influenza vaccination during pregnancy: a systematic review

OBJECTIVE

We conducted a systematic review to evaluate associations between influenza vaccination during pregnancy and adverse birth outcomes and maternal non-obstetric serious adverse events (SAEs), taking into consideration confounding and temporal biases.

METHODS

Electronic databases (Ovid MEDLINE ALL, Embase Classic+Embase and the Cochrane Central Register of Controlled Trials) were searched to June 2021 for observational studies assessing associations between influenza vaccination during pregnancy and maternal non-obstetric SAEs and adverse birth outcomes, including preterm birth, spontaneous abortion, stillbirth, small-for-gestational-age birth and congenital anomalies. Studies of live attenuated vaccines, single-arm cohort studies and abstract-only publications were excluded. Records were screened using a liberal accelerated approach initially, followed by a dual independent approach for full-text screening, data extraction and risk of bias assessment. Pairwise meta-analyses were conducted, where two or more studies met methodological criteria for inclusion. The Grading of Recommendations, Assessment, Development and Evaluation approach was used to assess evidence certainty.

RESULTS

Of 9443 records screened, 63 studies were included. Twenty-nine studies (24 cohort and 5 case-control) evaluated seasonal influenza vaccination (trivalent and/or quadrivalent) versus no vaccination and were the focus of our prioritised syntheses; 34 studies of pandemic vaccines (2009 A/H1N1 and others), combinations of pandemic and seasonal vaccines, and seasonal versus seasonal vaccines were also reviewed. Control for confounding and temporal biases was inconsistent across studies, limiting pooling of data. Meta-analyses for preterm birth, spontaneous abortion and small-for-gestational-age birth demonstrated no significant associations with seasonal influenza vaccination. Immortal time bias was observed in a sensitivity analysis of meta-analysing risk-based preterm birth data. In descriptive summaries for stillbirth, congenital anomalies and maternal non-obstetric SAEs, no significant association with increased risk was found in any studies. All evidence was of very low certainty.

CONCLUSIONS

Evidence of very low certainty suggests that seasonal influenza vaccination during pregnancy is not associated with adverse birth outcomes or maternal non-obstetric SAEs. Appropriate control of confounding and temporal biases in future studies would improve the evidence base.

Intraseasonal waning immunity of seasonal influenza vaccine - A systematic review and meta-analysis

BACKGROUND

Recently, studies have suggested that influenza antibody titers decline with time since vaccination. Duration of vaccine protection is an important factor to determine the optimal timing of vaccination.

OBJECTIVE

We aimed to systematically evaluate the implication of waning immunity on the duration of seasonal influenza vaccine antibody response.

METHOD

Electronic databases and clinical trial registries were systematically searched to identify phase III/IV randomized clinical trials evaluating the immunogenicity of seasonal influenza vaccines measured by hemagglutination inhibition assay in healthy individuals six months of age and older. Meta-analyses were conducted to compare adjuvanted and standard influenza vaccine responses with time since vaccination.

RESULTS

1918 articles were identified, of which ten were included in qualitative synthesis and seven in quantitative analysis (children; n=3, older adults; n=4). All studies were deemed to be at low risk of bias, except one study deemed at high risk of bias due to missing outcome data. The majority of included studies found a rise in antibody titers at one-month followed by a decline at six-month post-vaccination. At six-months post-vaccination overall risk differences in seroprotection were significantly higher for children vaccinated with adjuvanted compared to standard vaccines (0.29; 95 % confidence interval (CI), 0.14-0.44). A small increase in seroprotection levels was observed among older adults vaccinated with an adjuvanted compared to standard vaccines, which remained constant over six-months (pre-vaccination: 0.03; 95 % CI, 0.00-0.09 and one- and six-months post-vaccination: 0.05; 95 % CI, 0.01-0.09).

CONCLUSIONS

Our results found evidence of persistent antibody responses following influenza vaccination over the course of a typical influenza season. Even if influenza vaccine responses wane over a six-month period, vaccination likely still provides a significant advantage in protection, which may be enhanced with adjuvanted vaccines, particularly in children. Further research is needed to identify the exact timing when the decline in antibody response begins to better inform the optimal timing of influenza vaccination programs.

TRIAL REGISTRATION

PROSPERO (CRD42019138585).

Summary of the National Advisory Committee on Immunization (NACI) Statement-Recommendation on Repeated Seasonal Influenza Vaccination

Background

Influenza vaccination is recommended annually; however, some studies have raised questions regarding whether repeated influenza vaccine administration may have unintended negative consequences for seasonal protection.

Methods

The National Advisory Committee on Immunization (NACI) Influenza Working Group undertook an overview of systematic reviews on the effects of repeated influenza vaccination on vaccine effectiveness, efficacy, and immunogenicity. A systematic assessment of programmatic factors was conducted according to established NACI methods. The NACI evidence-based process was used to critically appraise the available evidence and to review recommendations.

Results

The evidence base consisted of four eligible systematic reviews/meta-analyses. Repeated vaccination, including the current season, was consistently more effective than no vaccination in the current season. The evidence showed no significant difference or predictable trend in vaccine efficacy or effectiveness between vaccinations in two consecutive seasons compared to vaccination in the current season only.

Conclusion

Overall, NACI concluded that there is evidence to recommend annual influenza vaccination, irrespective of whether an individual received the seasonal influenza vaccine in previous seasons. It is neither currently feasible nor warranted to modify existing annual influenza vaccination programs to account for potential negative or positive interference. NACI continues to strongly recommend that seasonal influenza vaccine should be offered annually to everyone six months of age and older who does not have contraindications to the vaccine, irrespective of previous seasons' influenza vaccination status.

Summary of the National Advisory Committee on Immunization (NACI) Statement-Recommendations on Fractional Influenza Vaccine Dosing in the Event of a Shortage: Pandemic preparedness

Background

At the commencement of a pandemic, it is important to consider the impact of respiratory infections on the health system and the possibility of vaccine shortages due to increased demand. In the event of an influenza vaccine shortage, a strategy for administration of fractional influenza vaccine doses might be considered. This article reviews the available evidence for efficacy, effectiveness, immunogenicity and safety of fractional influenza vaccine dosing, and summarizes the National Advisory Committee on Immunization (NACI) recommendations on fractional dosing strategies by public health programs in Canada.

Methods

Two rapid literature reviews were undertaken to evaluate the efficacy, effectiveness, immunogenicity and safety of fractional influenza vaccine dosing via the intramuscular or intradermal route. The NACI evidence-based process was used to assess the quality of eligible studies, summarize and analyze the findings, and apply an ethics, equity, feasibility and acceptability lens to develop recommendations.

Results

There was limited evidence for the effectiveness of fractional influenza vaccine dosing. Fractional dosing studies were primarily conducted in healthy individuals, mainly young children and infants, with no underlying chronic conditions. There was fair evidence for immunogenicity and safety. Feasibility issues were identified with intradermal use in particular.

Conclusion

NACI recommended that, in the event of a significant population-level shortage of influenza vaccine, a full-dose influenza vaccine should continue to be used, and existing vaccine supply should be prioritized for those considered to be at high risk or capable of transmitting to those at high risk of influenza-related complications or hospitalizations. NACI recommended against the use of fractional doses of influenza vaccine in any population.

Summary of the National Advisory Committee on Immunization (NACI) Seasonal Influenza Vaccine Statement for 2022-2023

Background

The National Advisory Committee on Immunization (NACI) reviews the evolving evidence on influenza immunization and provides annual recommendations regarding the use of authorized seasonal influenza vaccines to the Public Health Agency of Canada.

Objective

To summarize the NACI seasonal influenza vaccine recommendations for 2022-2023 and to highlight new recommendations and supporting evidence.

Methods

In the preparation of the Statement on Seasonal Influenza Vaccine for 2022-2023, NACI's Influenza Working Group followed the NACI evidence-based process for developing recommendations. The recommendations were then considered and approved by NACI in light of the available evidence.

Results

The following key updates and new recommendations have been made for the 2022-2023 season: 1) updated information/guidance on influenza vaccination in the context of the coronavirus disease 2019 (COVID-19) has been incorporated; 2) Supemtek™ recombinant influenza vaccine may be considered for use among the quadrivalent influenza vaccines offered to adults 18 years of age and older for annual influenza immunization; and 3) Flucelvax® Quad may be considered among the quadrivalent influenza vaccines offered to adults and children two years of age and older.

Conclusion

NACI continues to recommend that an age-appropriate influenza vaccine should be offered annually for all individuals aged six months of age and older who do not have contraindications to the vaccine, with particular focus on people at high risk of influenza-related complications or hospitalization, people capable of transmitting influenza to those at high risk, and other groups for whom influenza vaccination is particularly recommended.

Summary of the National Advisory Committee on Immunization (NACI) Supplemental Statement on Recombinant Influenza Vaccines

Background

Recombinant protein technology is a novel platform for influenza vaccine manufacturing that differs significantly from existing egg-based and mammalian cell culture-based technologies. Supemtek™ is the first and, to date, the only recombinant quadrivalent influenza vaccine (RIV4) authorized for use in Canada in adults aged 18 years and older. The objective is to review the available evidence for efficacy, effectiveness, immunogenicity and safety of RIV4, and to summarize the National Advisory Committee on Immunization (NACI) recommendation regarding the use of Supemtek.

Methods

A systematic literature review and meta-analysis on the vaccine efficacy, effectiveness, immunogenicity and safety of RIV4 in adults was conducted according to methodology specified a priori in a written protocol. NACI evidence-based process was used to assess the available evidence and develop a recommendation regarding the use of Supemtek.

Results

Ten eligible studies were included in the evidence synthesis. One randomized controlled trial (RCT) in adults aged 50 years and older provided evidence that RIV4 may potentially offer improved protection against laboratory-confirmed influenza A infection compared to standard egg-based influenza vaccines. Data from eight RCTs assessing immunogenicity and five RCTs and one post-marketing surveillance study assessing safety indicated that Supemtek is a safe, well tolerated, and immunogenic alternative to conventional egg-based influenza vaccines for adults.

Conclusion

There is fair evidence that Supemtek is effective, safe, and has non-inferior immunogenicity to comparable vaccines, based on direct evidence in adults 18 years of age and older; thus, NACI recommends that Supemtek may be considered among the seasonal influenza vaccines offered to adults 18 years of age and older for their annual influenza vaccination.