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Background Influenza causes significant morbidity and mortality and stresses hospital resources during periods of increased circulation. We evaluated the effectiveness of the 2019–2020 influenza vaccine against influenza-associated hospitalization in the United States. Methods We included adults hospitalized with acute respiratory illness at 14 hospitals and tested for influenza viruses by reserve-transcription polymerase chain reaction. Vaccine effectiveness (VE) was estimated by comparing the odds of current-season influenza vaccination in test-positive influenza cases vs test-negative controls, adjusting for confounders. VE was stratified by age and major circulating influenza types along with A(H1N1)pdm09 genetic subgroups. Results A total of 3116 participants were included, including 18% (n = 553) influenza-positive cases. Median age was 63 years. Sixty-seven percent (n = 2079) received vaccination. Overall adjusted VE against influenza viruses was 41% (95% confidence interval [CI], 27%–52%). VE against A(H1N1)pdm09 viruses was 40% (95% CI, 24%–53%) and 33% against B viruses (95% CI, 0–56%). Of the 2 major A(H1N1)pdm09 subgroups (representing 90% of sequenced H1N1 viruses), VE against one group (5A + 187A,189E) was 59% (95% CI, 34%–75%) whereas no VE was observed against the other group (5A + 156K) (–1% [95% CI, –61% to 37%]). Conclusions In a primarily older population, influenza vaccination was associated with a 41% reduction in risk of hospitalized influenza illness.

We estimated vaccine effectiveness (VE) for prevention of influenza-associated hospitalizations among adults during the 2018–2019 influenza season. Adults admitted with acute respiratory illness to 14 hospitals of the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) and testing positive for influenza were cases; patients testing negative were controls. VE was estimated using logistic regression and inverse probability of treatment weighting. We analyzed data from 2863 patients with a mean age of 63 years. Adjusted VE against influenza A(H1N1)pdm09–associated hospitalization was 51% (95% confidence interval [CI], 25%–68%). Adjusted VE against influenza A(H3N2) virus–associated hospitalization was −2% (95% CI, −65% to 37%) and differed significantly by age, with VE of −130% (95% CI, −374% to −27%) among adults 18 to ≤56 years of age. Although vaccination halved the risk of influenza A(H1N1)pdm09–associated hospitalizations, it conferred no protection against influenza A(H3N2)–associated hospitalizations. We observed negative VE for young and middle-aged adults but cannot exclude residual confounding as a potential explanation.

Background Parainfluenza virus (PIV) is a leading cause of acute respiratory illness (ARI) in children. However, few studies have characterized the clinical features and outcomes associated with PIV infections among young children in the Middle East. Methods We conducted hospital-based surveillance for ARI among children Results PIV was detected in 221/3168 (7.0%) children hospitalized with ARI. PIV-3 was the most commonly detected serotype (125/221; 57%). Individual clinical features of PIV infections varied little by individual serotype, although admission diagnosis of ‘croup’ was only associated with PIV-1 and PIV-2. Children with PIV-associated ARI had lower frequency of cough (71% vs 83%; p p = 0.68) and infections in which no virus was detected. Conclusions PIV is frequently associated with ARI requiring hospitalization in young Jordanian children. Substantial overlap in clinical features may preclude distinguishing PIV infections from other viral infections at presentation.

Background Human coronaviruses (HCoVs) are a significant cause of acute respiratory illness (ARI) in children; however, the role of HCoVs in ARI among hospitalized children in the Middle East is not well defined. Methods Children under 2 years admitted with fever and/or respiratory symptoms were enrolled from 2010 to 2013 in Amman, Jordan. Nasal/throat swabs were collected and stored for testing. Demographic and clinical characteristics were collected through parent/guardian interviews and medical chart abstractions. Prior stored specimens were tested for HCoVs (HKU1, OC43, 229E and NL63) by qRT-PCR. Results Of the 3168 children enrolled, 6.7% were HCoVs-positive. Among HCoV-positive children, the median age was 3.8 (1.9-8.4) months, 59% were male, 14% were premature, 11% had underlying medical conditions and 76% had viral-codetection. The most common presenting symptoms were cough, fever, wheezing and shortness of breath. HCoVs were detected year-round, peaking in winter-spring months. Overall, 56%, 22%, 13% and 6% were OC43, NL63, HKU1 and 229E, respectively. There was no difference in disease severity between the species, except higher intensive care unit admission frequency in NL63-positive subjects. Conclusions HCoVs were detected in around 7% of children enrolled in our study. Despite HCoV detection in children with ARI with highest peaks in respiratory seasons, the actual burden and pathogenic role of HCoVs in ARI merits further evaluation given the high frequency of viral codetection.