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Background Estimates of influenza disease burden are broadly useful for public health, helping national and local authorities monitor epidemiologic trends, plan and allocate resources, and promote influenza vaccination. Historically, estimates of the burden of seasonal influenza in the United States, focused mainly on influenza‐related mortality and hospitalization, were generated every few years. Since the 2010‐2011 influenza season, annual US influenza burden estimates have been generated and expanded to include estimates of influenza‐related outpatient medical visits and symptomatic illness in the community. Methods We used routinely collected surveillance data, outbreak field investigations, and proportions of people seeking health care from survey results to estimate the number of illnesses, medical visits, hospitalizations, and deaths due to influenza during six influenza seasons (2010‐2011 through 2015‐2016). Results We estimate that the number of influenza‐related illnesses that have occurred during influenza season has ranged from 9.2 million to 35.6 million, including 140 000 to 710 000 influenza‐related hospitalizations. Discussion These annual efforts have strengthened public health communications products and supported timely assessment of the impact of vaccination through estimates of illness and hospitalizations averted. Additionally, annual estimates of influenza burden have highlighted areas where disease surveillance needs improvement to better support public health decision making for seasonal influenza epidemics as well as future pandemics.

Increasing use of immunosuppressive biologic therapies poses a challenge for infectious diseases. Immunosuppressed patients have a high risk for influenza complications and an impaired immune response to vaccines. The total burden of immunosuppressive conditions in the United States, including those receiving emerging biologic therapies, remains unknown. We used the national claims database MarketScan to estimate the prevalence of immunosuppressive conditions and risk for acute respiratory illnesses (ARIs). We studied 47.2 million unique enrollees, representing 115 million person-years of observation during 2012-2017, and identified immunosuppressive conditions in 6.2% adults 18-64 years of age and 2.6% of children <18 years of age. Among 542,105 ARI hospitalizations, 32% of patients had immunosuppressive conditions. The risk for ARI hospitalizations was higher among enrollees with immunosuppression than among nonimmunosuppressed enrollees. Future efforts should focus on developing improved strategies, including vaccines, for preventing influenza in immunosuppressed patients, who are an increasing population in the United States.

During February 7─September 3, 2022, a total of 39 US states experienced outbreaks of highly pathogenic avian influenza A(H5N1) virus in birds from commercial poultry farms and backyard flocks. Among persons exposed to infected birds, highly pathogenic avian influenza A(H5) viral RNA was detected in 1 respiratory specimen from 1 person.

Repeat vaccination with egg-based influenza vaccines could preferentially boost antibodies targeting the egg-adapted epitopes and reduce immunogenicity to circulating viruses. In this randomized trial (Clinicaltrials.gov: NCT03722589), sera pre- and post-vaccination with quadrivalent inactivated egg-based (IIV4), cell culture-based (ccIIV4), and recombinant (RIV4) influenza vaccines were collected from healthcare personnel (18-64 years) in 2018−19 ( N  = 723) and 2019−20 ( N  = 684) influenza seasons. We performed an exploratory analysis. Vaccine egg-adapted changes had the most impact on A(H3N2) immunogenicity. In year 1, RIV4 induced higher neutralizing and total HA head binding antibodies to cell- A(H3N2) virus than ccIIV4 and IIV4. In year 2, among the 7 repeat vaccination arms (IIV4-IIV4, IIV4-ccIIV4, IIV4-RIV4, RIV4-ccIIV4, RIV4-RIV4, ccIIV4-ccIIV4 and ccIIV4-RIV4), repeat vaccination with either RIV4 or ccIIV4 further improved antibody responses to circulating viruses with decreased neutralizing antibody egg/cell ratio. RIV4 also had higher post-vaccination A(H1N1)pdm09 and A(H3N2) HA stalk antibodies in year 1, but there was no significant difference in HA stalk antibody fold rise among vaccine groups in either year 1 or year 2. Multiple seasons of non-egg-based vaccination may be needed to redirect antibody responses from immune memory to egg-adapted epitopes and re-focus the immune responses towards epitopes on the circulating viruses to improve vaccine effectiveness. Here the authors report an exploratory analysis of a clinical trial that tested different influenza virus vaccination platforms. The results show that multiple seasons of recombinant or cell-based influenza vaccinations may be needed to redirect antibody responses away from immune memory to egg-adapted epitopes and refocus on epitopes on the circulating viruses.

Background. Widespread use of pneumococcal conjugate vaccine (PCV7) resulted in decreases in invasive disease among children and elderly persons. The benefits may be offset by increases in disease due to serotypes not included in the vaccine (hereafter, \"nonvaccine serotypes\"). We evaluated the effect of PCV7 on incidence of disease due to nonvaccine serotypes. Methods. Cases of invasive disease were identified in 8 geographic areas through the Centers for Disease Control and Prevention's Active Bacterial Core surveillance. Serotyping and susceptibility testing of isolates were performed. We calculated the incidence of disease for children aged <5 years and adults aged ⩾65 years. We compared rates of serotype-specific disease before and after PCV7 was licensed for use. Results. The annual incidence of disease due to nonvaccine serotypes increased from an average of 16.3 cases/100,000 population during prevaccine years (1998–1999) to 19.9 cases/100,000 population in 2004 for children aged <5 years (P=.01) and from 27.0 cases/100,000 population during prevaccine years to 29.8 cases/100,000 population in 2004 for adults aged ⩾65 years (P=.05). Significant increases in the incidences of disease due to serotypes 3, 15, 19A, 22F, and 33F were observed among children during this period (P<.05 for each serotype); serotype 19A has become the predominant cause of invasive disease in children. The incidence of disease due to these serotypes also increased among elderly persons. Conclusions. The incidence of pneumococcal disease caused by nonvaccine serotypes is increasing. Ongoing surveillance is needed to monitor the magnitude of disease caused by nonvaccine serotypes, to ensure that future vaccines target the appropriate serotypes.

Elevated body mass index (BMI) has been linked to severe influenza illness and impaired vaccine immunogenicity, but the relationship between BMI and clinical vaccine effectiveness (VE) is less well described. This secondary analysis of data from a test-negative study of outpatients with acute respiratory illness assessed BMI and VE against medically attended, PCR-confirmed influenza over seven seasons (2011–12 through 2017–18). Vaccination status was determined from electronic medical records (EMR) and self-report; BMI was estimated from EMR-documented height and weight categorized for adults as obesity (≥ 30 kg/m 2 ), overweight (25–29 kg/m 2 ), or normal and for children based on standardized z-scales. Current season VE by virus type/subtype was estimated separately for adults and children. Pooled VE for all seasons was calculated as 1—adjusted odds ratios from logistic regression with an interaction term for BMI and vaccination. Among 28,089 adults and 12,380 children, BMI category was not significantly associated with VE against outpatient influenza for any type/subtype. Adjusted VE against A/H3N2, A/H1N1pdm09, and B in adults ranged from 16–31, 46–54, and 44–57%, and in children from 29–34, 57–65, and 50–55%, respectively, across the BMI categories. Elevated BMI was not associated with reduced VE against laboratory confirmed, outpatient influenza illness.

We assessed determinants of work attendance during the first 3 days after onset of acute respiratory illness (ARI) among workers 19-64 years of age who had medically attended ARI or influenza during the 2017-2018 influenza season. The total number of days worked included days worked at the usual workplace and days teleworked. Access to paid leave was associated with fewer days worked overall and at the usual workplace during illness. Participants who indicated that employees were discouraged from coming to work with influenza-like symptoms were less likely to attend their usual workplace. Compared with workers without a telework option, those with telework access worked more days during illness overall, but there was no difference in days worked at the usual workplace. Both paid leave benefits and business practices that actively encourage employees to stay home while sick are necessary to reduce the transmission of ARI and influenza in workplaces.

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 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.

In 2006, Brazil began routine immunization of infants <15 wk of age with a single-strain rotavirus vaccine. We evaluated whether the rotavirus vaccination program was associated with declines in childhood diarrhea deaths and hospital admissions by monitoring disease trends before and after vaccine introduction in all five regions of Brazil with varying disease burden and distinct socioeconomic and health indicators. National data were analyzed with an interrupted time-series analysis that used diarrhea-related mortality or hospitalization rates as the main outcomes. Monthly mortality and admission rates estimated for the years after rotavirus vaccination (2007-2009) were compared with expected rates calculated from pre-vaccine years (2002-2005), adjusting for secular and seasonal trends. During the three years following rotavirus vaccination in Brazil, rates for diarrhea-related mortality and admissions among children <5 y of age were 22% (95% confidence interval 6%-44%) and 17% (95% confidence interval 5%-27%) lower than expected, respectively. A cumulative total of ~1,500 fewer diarrhea deaths and 130,000 fewer admissions were observed among children <5 y during the three years after rotavirus vaccination. The largest reductions in deaths (22%-28%) and admissions (21%-25%) were among children younger than 2 y, who had the highest rates of vaccination. In contrast, lower reductions in deaths (4%) and admissions (7%) were noted among children two years of age and older, who were not age-eligible for vaccination during the study period. After the introduction of rotavirus vaccination for infants, significant declines for three full years were observed in under-5-y diarrhea-related mortality and hospital admissions for diarrhea in Brazil. The largest reductions in diarrhea-related mortality and hospital admissions for diarrhea were among children younger than 2 y, who were eligible for vaccination as infants, which suggests that the reduced diarrhea burden in this age group was associated with introduction of the rotavirus vaccine. These real-world data are consistent with evidence obtained from clinical trials and strengthen the evidence base for the introduction of rotavirus vaccination as an effective measure for controlling severe and fatal childhood diarrhea.

Persons with COVID-19-like illnesses are advised to stay home to reduce the spread of SARS-CoV-2. We assessed relationships between telework experience and COVID-19 illness with work attendance when ill. Adults experiencing fever, cough, or loss of taste or smell who sought healthcare or COVID-19 testing in the United States during March-November 2020 were enrolled. Adults with telework experience before illness were more likely to work at all (onsite or remotely) during illness (87.8%) than those with no telework experience (49.9%) (adjusted odds ratio 5.48, 95% CI 3.40-8.83). COVID-19 case-patients were less likely to work onsite (22.1%) than were persons with other acute respiratory illnesses (37.3%) (adjusted odds ratio 0.36, 95% CI 0.24-0.53). Among COVID-19 case-patients with telework experience, only 6.5% worked onsite during illness. Telework experience before illness gave mildly ill workers the option to work and improved compliance with public health recommendations to stay home during illness.