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In the United States, annual vaccination against seasonal influenza is recommended for all persons aged ≥6 months (1). Each influenza season since 2004-05, CDC has estimated the effectiveness of seasonal influenza vaccine to prevent influenza-associated, medically attended, acute respiratory illness (ARI). This report uses data, as of February 4, 2017, from 3,144 children and adults enrolled in the U.S. Influenza Vaccine Effectiveness Network (U.S. Flu VE Network) during November 28, 2016-February 4, 2017, to estimate an interim adjusted effectiveness of seasonal influenza vaccine for preventing laboratory-confirmed influenza virus infection associated with medically attended ARI. During this period, overall vaccine effectiveness (VE) (adjusted for study site, age group, sex, race/ethnicity, self-rated general health, and days from illness onset to enrollment) against influenza A and influenza B virus infection associated with medically attended ARI was 48% (95% confidence interval [CI] = 37%-57%). Most influenza infections were caused by A (H3N2) viruses. VE was estimated to be 43% (CI = 29%-54%) against illness caused by influenza A (H3N2) virus and 73% (CI = 54%-84%) against influenza B virus. These interim VE estimates indicate that influenza vaccination reduced the risk for outpatient medical visits by almost half. Because influenza activity remains elevated (2), CDC and the Advisory Committee on Immunization Practices recommend that annual influenza vaccination efforts continue as long as influenza viruses are circulating (1). Vaccination with 2016-17 influenza vaccines will reduce the number of infections with most currently circulating influenza viruses. Persons aged ≥6 months who have not yet been vaccinated this season should be vaccinated as soon as possible. [ABSTRACT FROM AUTHOR]

Background: During the 2014-2015 US influenza season, expanded genetic characterization of circulating influenza A(H3N2) viruses was used to assess the impact of the genetic variability of influenza A(H3N2) viruses on influenza vaccine effectiveness (VE).Methods: A novel pyrosequencing assay was used to determine genetic group, based on hemagglutinin (HA) gene sequences, of influenza A(H3N2) viruses from patients enrolled at US Influenza Vaccine Effectiveness Network sites. VE was estimated using a test-negative design comparing vaccination among patients infected with influenza A(H3N2) viruses and uninfected patients.Results: Among 9710 enrollees, 1868 (19%) tested positive for influenza A(H3N2) virus; genetic characterization of 1397 viruses showed that 1134 (81%) belonged to 1 HA genetic group (3C.2a) of antigenically drifted influenza A(H3N2) viruses. Effectiveness of 2014-2015 influenza vaccination varied by influenza A(H3N2) virus genetic group from 1% (95% confidence interval [CI], -14% to 14%) against illness caused by antigenically drifted influenza A(H3N2) virus group 3C.2a viruses versus 44% (95% CI, 16%-63%) against illness caused by vaccine-like influenza A(H3N2) virus group 3C.3b viruses.Conclusions: Effectiveness of 2014-2015 influenza vaccination varied by genetic group of influenza A(H3N2) virus. Changes in HA genes related to antigenic drift were associated with reduced VE. [ABSTRACT FROM AUTHOR]

Background. Influenza causes significant morbidity and mortality, with considerable economic costs, including lost work productivity. Influenza vaccines may reduce the economic burden through primary prevention of influenza and reduction in illness severity. Methods. We examined illness severity and work productivity loss among working adults with medically attended acute respiratory illnesses and compared outcomes for subjects with and without laboratory-confirmed influenza and by influenza vaccination status among subjects with influenza during the 2012-2013 influenza season. Results. Illnesses laboratory-confirmed as influenza (ie, cases) were subjectively assessed as more severe than illnesses not caused by influenza (ie, noncases) based on multiple measures, including current health status at study enrollment (≤7 days from illness onset) and current activity and sleep quality status relative to usual. Influenza cases reported missing 45% more work hours (20.5 vs 15.0; P < .001) than noncases and subjectively assessed their work productivity as impeded to a greater degree (6.0 vs 5.4; P < .001). Current health status and current activity relative to usual were subjectively assessed as modestly but significantly better for vaccinated cases compared with unvaccinated cases; however, no significant modifications of sleep quality, missed work hours, or work productivity loss were noted for vaccinated subjects. Conclusions. Influenza illnesses were more severe and resulted in more missed work hours and productivity loss than illnesses not confirmed as influenza. Modest reductions in illness severity for vaccinated cases were observed. These findings highlight the burden of influenza illnesses and illustrate the importance of laboratory confirmation of influenza outcomes in evaluations of vaccine effectiveness. [ABSTRACT FROM AUTHOR]

Background. During the 2012-2013 influenza season, there was cocirculation of influenza A(H3N2) and 2 influenza B lineage viruses in the United States. Methods. Patients with acute cough illness for ⩽7 days were prospectively enrolled and had swab samples obtained at outpatient clinics in 5 states. Influenza vaccination dates were confirmed by medical records. The vaccine effectiveness (VE) was estimated as [100% × (1 - adjusted odds ratio)] for vaccination in cases versus test-negative controls. Results. Influenza was detected in 2307 of 6452 patients (36%); 1292 (56%) had influenza A(H3N2), 582 (25%) had influenza B/Yamagata, and 303 (13%) had influenza B/Victoria. VE was 49% (95% confidence interval [CI], 43%-55%) overall, 39% (95% CI, 29%-47%) against influenza A(H3N2), 66% (95% CI, 58%-73%) against influenza B/Yamagata (vaccine lineage), and 51% (95% CI, 36%-63%) against influenza B/Victoria. VE against influenza A(H3N2) was highest among persons aged 50-64 years (52%; 95% CI, 33%-65%) and persons aged 6 months- 8 years (51%; 95% CI, 32%-64%) and lowest among persons aged ⩾65 years (11%; 95% CI, -41% to 43%). In younger age groups, there was evidence of residual protection from receipt of the 2011-2012 vaccine 1 year earlier. Conclusions. The 2012-2013 vaccines were moderately effective in most age groups. Cross-lineage protection and residual effects from prior vaccination were observed and warrant further investigation. [ABSTRACT FROM AUTHOR]

The article presents an early estimate of seasonal influenza vaccine effectiveness for prevention of influenza virus infection associated with acute respiratory illness (ARI) in the U.S. Of the more than two thousand children and adults with ARI enrolled at the study sites, more than forty percent tested positive for influenza virus.

During the 2012–2013 influenza season, antiviral treatment was underutilized and antibiotics may have been overused among clinicians providing care to outpatients with laboratory-confirmed influenza.Background. Early antiviral treatment (≤2 days since illness onset) of influenza reduces the probability of influenza-associated complications. Early empiric antiviral treatment is recommended for those with suspected influenza at higher risk for influenza complications regardless of their illness severity. We describe antiviral receipt among outpatients with acute respiratory illness (ARI) and antibiotic receipt among patients with influenza.Methods. We analyzed data from 5 sites in the US Influenza Vaccine Effectiveness Network Study during the 2012–2013 influenza season. Subjects were outpatients aged ≥6 months with ARI defined by cough of ≤7 days’ duration; all were tested for influenza by polymerase chain reaction (PCR). Medical history and prescription information were collected by medical and pharmacy records. Four sites collected prescribing data on 3 common antibiotics (amoxicillin-clavulanate, amoxicillin, and azithromycin).Results. Of 6766 enrolled ARI patients, 509 (7.5%) received an antiviral prescription. Overall, 2366 (35%) had PCR-confirmed influenza; 355 (15%) of those received an antiviral prescription. Among 1021 ARI patients at high risk for influenza complications (eg, aged <2 years or ≥65 years or with ≥1 chronic medical condition) presenting to care ≤2 days from symptom onset, 195 (19%) were prescribed an antiviral medication. Among participants with PCR-confirmed influenza and antibiotic data, 540 of 1825 (30%) were prescribed 1 of 3 antibiotics; 297 of 1825 (16%) were prescribed antiviral medications.Conclusions. Antiviral treatment was prescribed infrequently among outpatients with influenza for whom therapy would be most beneficial; in contrast, antibiotic prescribing was more frequent. Continued efforts to educate clinicians on appropriate antibiotic and antiviral use are essential to improve healthcare quality. [ABSTRACT FROM AUTHOR]

This article presents information on the interim estimation of the effectiveness of seasonal influenza vaccine by the U.S. Centers for Disease Control and Prevention from 2013 to 2014. It mentions the objective of this report by the CDC, the methods used by the U.S. Flu Vaccine Effectiveness Network in its study of vaccine effectiveness and the growth in influenza activity in the country.

Influenza vaccine effectiveness in preventing medically attended influenza in the 2011–2012 season was modest overall, with low effectiveness against the predominant A (H3N2) virus. This may be related to antigenic drift, but past history of vaccination might also play a role.Background. Each year, the US Influenza Vaccine Effectiveness Network examines the effectiveness of influenza vaccines in preventing medically attended acute respiratory illnesses caused by influenza.Methods. Patients with acute respiratory illnesses of ≤7 days’ duration were enrolled at ambulatory care facilities in 5 communities. Specimens were collected and tested for influenza by real-time reverse-transcriptase polymerase chain reaction. Receipt of influenza vaccine was defined based on documented evidence of vaccination in medical records or immunization registries. Vaccine effectiveness was estimated in adjusted logistic regression models by comparing the vaccination coverage in those who tested positive for influenza with those who tested negative.Results. The 2011–2012 season was mild and peaked late, with circulation of both type A viruses and both lineages of type B. Overall adjusted vaccine effectiveness was 47% (95% confidence interval [CI], 36–56) in preventing medically attended influenza; vaccine effectiveness was 65% (95% CI, 44–79) against type A (H1N1) pdm09 but only 39% (95% CI, 23–52) against type A (H3N2). Estimates of vaccine effectiveness against both type B lineages were similar (overall, 58%; 95% CI, 35–73). An apparent negative effect of prior year vaccination on current year effectiveness estimates was noted, particularly for A (H3N2) outcomes.Conclusions. Vaccine effectiveness in the 2011–2012 season was modest overall, with lower effectiveness against the predominant A (H3N2) virus. This may be related to antigenic drift, but past history of vaccination might also play a role. [ABSTRACT FROM PUBLISHER]