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Importance: Understanding the susceptibility and infectiousness of children and adolescents in comparison to adults is important to appreciate their role in the COVID-19 pandemic. Objective: To determine SARS-CoV-2 susceptibility and infectiousness of children and adolescents with adults as comparator for three variants (wild-type, alpha, delta) in the household setting. We aimed to identify the effects independent of vaccination or prior infection. Data sources: We searched EMBASE, PubMed and medRxiv up to January 2022. Study selection: Two reviewers independently identified studies providing secondary household attack rates (SAR) for SARS-CoV-2 infection in children (0–9 years), adolescents (10–19 years) or both compared with adults (20 years and older). Data extraction and synthesis: Two reviewers independently extracted data, assessed risk of bias and performed a random-effects meta-analysis model. Main outcomes and measures: Odds ratio (OR) for SARS-CoV-2 infection comparing children and adolescents with adults stratified by wild-type (ancestral type), alpha, and delta variant, respectively. Susceptibility was defined as the secondary attack rate (SAR) among susceptible household contacts irrespective of the age of the index case. Infectiousness was defined as the SAR irrespective of the age of household contacts when children/adolescents/adults were the index case. Results: Susceptibility analysis: We included 27 studies (308,681 contacts), for delta only one (large) study was available. Compared to adults, children and adolescents were less susceptible to the wild-type and delta, but equally susceptible to alpha. Infectiousness analysis: We included 21 studies (201,199 index cases). Compared to adults, children and adolescents were less infectious when infected with the wild-type and delta. Alpha -related infectiousness remained unclear, 0–9 year old children were at least as infectious as adults. Overall SAR among household contacts varied between the variants. Conclusions and relevance: When considering the potential role of children and adolescents, variant-specific susceptibility, infectiousness, age group and overall transmissibility need to be assessed. [ABSTRACT FROM AUTHOR]

The most effective means of preventing seasonal influenza is through vaccination. In this systematic review, we investigated the efficacy, effectiveness and safety of MF59® adjuvanted trivalent and quadrivalent influenza vaccines to prevent laboratory‐confirmed influenza. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials and non‐randomised studies of interventions (NRSIs) were eligible for inclusion. The search returned 28,846 records, of which 48 studies on MF59® adjuvanted vaccines met our inclusion criteria. No efficacy trials were identified. In terms of vaccine effectiveness (VE), MF59® adjuvanted trivalent influenza vaccines were effective in preventing laboratory‐confirmed influenza in older adults (aged ≥65 years) compared with no vaccination (VE = 45%, 95% confidence interval (CI) 23%–61%, 5 NRSIs across 3 influenza seasons). By subtype, significant effect was found for influenza A(H1N1) (VE = 61%, 95% CI 44%–73%) and B (VE = 29%, 95% CI 5%–46%), but not for A(H3N2). In terms of relative VE, there was no significant difference comparing MF59® adjuvanted trivalent vaccines with either non‐adjuvanted trivalent or quadrivalent vaccines. Compared with traditional trivalent influenza vaccines, MF59® adjuvanted trivalent influenza vaccines were associated with a greater number of local adverse events (RR = 1.90, 95% CI 1.50–2.39) and systemic reactions (RR = 1.18, 95% CI 1.02–1.38). In conclusion, MF59® adjuvanted trivalent influenza vaccines were found to be more effective than 'no vaccination'. Based on limited data, there was no significant difference comparing the effectiveness of MF59® adjuvanted vaccines with their non‐adjuvanted counterparts. [ABSTRACT FROM AUTHOR]

The most effective means of preventing seasonal influenza is through vaccination. In this systematic review, we investigated the efficacy, effectiveness and safety of recombinant haemagglutinin (HA) seasonal influenza vaccines to prevent laboratory‐confirmed influenza. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials and non‐randomised studies of interventions were eligible for inclusion. The search returned 28,846 records, of which 10 studies on recombinant HA influenza vaccine met our inclusion criteria. One study found that the quadrivalent recombinant HA influenza vaccine had higher relative vaccine efficacy (rVE) in preventing laboratory‐confirmed influenza during the 2014–15 season compared with traditional quadrivalent vaccination in adults aged ≥50 years (rVE = 30%, 95% CI 10%–47%, moderate‐certainty evidence). In a subgroup analysis, higher rVE was reported for influenza A (rVE = 36%, 95% CI 14% to 53%), but not for B (non‐significant). Another study reported higher efficacy for the trivalent recombinant HA vaccine compared with placebo (VE = 45%, 95% CI 19–63, 1 RCT, low‐certainty evidence) in adults aged 18–55 years. With the exception of a higher rate of chills (RR = 1.33, 95% CI 1.03–1.72), the safety profile of recombinant HA vaccines was comparable to that of traditional influenza vaccines. The evidence base for the efficacy and effectiveness of recombinant HA influenza vaccines is limited at present, although one study found that the quadrivalent recombinant HA influenza vaccine had higher rVE compared with traditional quadrivalent vaccination in adults aged ≥50 years. [ABSTRACT FROM AUTHOR]

The most effective means of preventing seasonal influenza is through strain‐specific vaccination. In this study, we investigated the efficacy, effectiveness and safety of cell‐based trivalent and quadrivalent influenza vaccines. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials (RCTs) and non‐randomised studies of interventions (NRSIs) were eligible for inclusion. Two reviewers independently screened, extracted data and assessed the risk of bias of included studies. Certainty of evidence for key outcomes was assessed using the GRADE methodology. The search returned 28,846 records, of which 868 full‐text articles were assessed for relevance. Of these, 19 studies met the inclusion criteria. No relative efficacy data were identified for the direct comparison of cell‐based vaccines compared with traditional vaccines (egg‐based). Efficacy data were available comparing cell‐based trivalent influenza vaccines with placebo in adults (aged 18–49 years). Overall vaccine efficacy was 70% against any influenza subtype (95% CI 61%–77%, two RCTS), 82% against influenza A(H1N1) (95% CI 71%–89%, 2 RCTs), 72% against influenza A(H3N2) (95% CI 39%–87%, 2 RCTs) and 52% against influenza B (95% CI 30%–68%, 2 RCTs). Limited and heterogeneous data were presented for effectiveness when compared with no vaccination. One NRSI compared cell‐based trivalent and quadrivalent vaccination with traditional trivalent and quadrivalent vaccination, finding a small but significant difference in favour of cell‐based vaccines for influenza‐related hospitalisation, hospital encounters and physician office visits. The safety profile of cell‐based trivalent vaccines was comparable to traditional trivalent influenza vaccines. Compared with placebo, cell‐based trivalent influenza vaccines have demonstrated greater efficacy in adults aged 18–49 years. Overall cell‐based vaccines are well‐tolerated in adults, however, evidence regarding the effectiveness of these vaccines compared with traditional seasonal influenza vaccines is limited. [ABSTRACT FROM AUTHOR]

This review sought to assess the efficacy, effectiveness and safety of high‐dose inactivated influenza vaccines (HD‐IIV) for the prevention of laboratory‐confirmed influenza in individuals aged 18 years or older. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials (RCTs) and non‐randomised studies of interventions (NRSIs) were included. The search returned 28,846 records, of which 36 studies were included. HD‐IIV was shown to have higher relative vaccine efficacy in preventing influenza compared with standard‐dose influenza vaccines (SD‐IIV3) in older adults (Vaccine effectiveness (VE) = 24%, 95% CI 10–37, one RCT). One NRSI demonstrated significant effect for HD‐IIV3 against influenza B (VE = 89%, 95% CI 47–100), but not for influenza A(H3N2) (VE = 22%, 95% CI −82 to 66) when compared with no vaccination in older adults. HD‐IIV3 showed significant relative effect compared with SD‐IIV3 for influenza‐related hospitalisation (VE = 11.8%, 95% CI 6.4–17.0, two NRSIs), influenza‐ or pneumonia‐related hospitalisation (VE = 13.7%, 95% CI 9.5–17.7, three NRSIs), influenza‐related hospital encounters (VE = 13.1%, 95% CI 8.4–17.7, five NRSIs), and influenza‐related office visits (VE = 3.5%, 95% CI 1.5–5.5, two NRSIs). For safety, HD‐IIV were associated with significantly higher rates of local and systemic adverse events compared with SD‐IIV (combined local reactions, pain at injection site, swelling, induration, headache, chills and malaise). From limited data, compared with SD‐IIV, HD‐IIV were found to be more effective in the prevention of laboratory‐confirmed influenza, for a range of proxy outcome measures, and associated with more adverse events. [ABSTRACT FROM AUTHOR]

Background: A population‐based pregnancy cohort was established in Norway to study potential effects of exposure to the 2009 influenza pandemic or pandemic vaccination during pregnancy. Objectives: We studied maternal A(H1N1)pdm09‐specific hemagglutination inhibition (HI)‐titer levels and waning in women with influenza‐like illness (ILI) in pregnancy compared to vaccinated women. Moreover, we studied the association between HI‐titers and self‐reported severity and duration of ILI. Methods: HI‐titers against the pandemic virus were measured in maternal blood samples obtained at birth, 3‐9 months after exposure, and linked with information about pregnancy, influenza and vaccination from national registries and a cohort questionnaire. Results: Among 1821 pregnant women included, 43.7% were unvaccinated and 19.3% of these had ILI. HI‐titers were low (geometric mean titer (GMT) 11.3) in the unvaccinated women with ILI. Higher HI‐titers (GMT 37.8) were measured in the vaccinated women. Estimated HI‐titer waning was similar for vaccinated women and women with ILI. Most ILI episodes were moderate and lasted 3‐5 days. Women with ILI reporting specific influenza symptoms such as fever or cough had higher HI‐titers than women without these symptoms. Women who reported being "very ill" or illness duration of >5 days had higher HI‐titers than women reporting less severe illness or illness of shorter duration, respectively. Conclusions: Antibody waning was similar in vaccinated women and women with ILI. More severe ILI or longer duration of illness was associated with higher HI‐titers. Most unvaccinated pregnant women with ILI had low HI‐titers, probably due to moderate illness and HI‐titer waning between exposure and sampling. [ABSTRACT FROM AUTHOR]

The most effective means of preventing seasonal influenza is through vaccination. In this systematic review, we investigated the efficacy, effectiveness and safety of MF59 ® adjuvanted trivalent and quadrivalent influenza vaccines to prevent laboratory-confirmed influenza. A systematic literature search was conducted in electronic databases and grey literature sources up to 7 February 2020. Randomised controlled trials and non-randomised studies of interventions (NRSIs) were eligible for inclusion. The search returned 28,846 records, of which 48 studies on MF59 ® adjuvanted vaccines met our inclusion criteria. No efficacy trials were identified. In terms of vaccine effectiveness (VE), MF59 ® adjuvanted trivalent influenza vaccines were effective in preventing laboratory-confirmed influenza in older adults (aged ≥65 years) compared with no vaccination (VE = 45%, 95% confidence interval (CI) 23%-61%, 5 NRSIs across 3 influenza seasons). By subtype, significant effect was found for influenza A(H1N1) (VE = 61%, 95% CI 44%-73%) and B (VE = 29%, 95% CI 5%-46%), but not for A(H3N2). In terms of relative VE, there was no significant difference comparing MF59 ® adjuvanted trivalent vaccines with either non-adjuvanted trivalent or quadrivalent vaccines. Compared with traditional trivalent influenza vaccines, MF59 ® adjuvanted trivalent influenza vaccines were associated with a greater number of local adverse events (RR = 1.90, 95% CI 1.50-2.39) and systemic reactions (RR = 1.18, 95% CI 1.02-1.38). In conclusion, MF59 ® adjuvanted trivalent influenza vaccines were found to be more effective than 'no vaccination'. Based on limited data, there was no significant difference comparing the effectiveness of MF59 ® adjuvanted vaccines with their non-adjuvanted counterparts., (© 2022 John Wiley & Sons Ltd.)