Influenza vaccine effectiveness among elderly persons living in the community during the 2003--2004 season

To examine the effectiveness of influenza vaccine among community-dwelling elderly (65-79 years old), we conducted a population-based cohort study during the 2003--2004 influenza season. A total of 4787 elderly individuals were interviewed regarding acute febrile illness, hospital visits, hospitalization and death by telephone every month. The vaccination status and physician-diagnosed clinical influenza (hereinafter referred as clinical influenza) were determined based on data obtained from the city office and hospitals, respectively. After adjusting for confounders, the odds ratio (OR) of vaccination for influenza-like illness (ILI) with high-fever, which was defined as an acute febrile illness (> or =38.5 degrees C) during the epidemic period, was 0.38 (95% confidence interval [CI], 0.17-0.85) and the OR for clinical influenza was 0.76 (95%CI, 0.28-2.06). Due to the inadequate sample size, ORs for preventing hospitalization for influenza or pneumonia (OR, 0.37; 95%CI, 0.09-1.47) and death (OR, 3.68; 95%CI, 0.75-18.12) were not conclusive. These results suggested that vaccination was therefore effective for elderly persons living in the community.     

Influenza vaccination coverage among persons aged 50-64 years enrolled in commercial managed health-care plans--United States, 2003-04 and 2004-05 influenza seasons

To combat an unexpected shortage of influenza vaccine in the fall of 2004, CDC issued guidance to direct available vaccine supplies to persons in designated priority groups (e.g., persons aged >/=65 years, persons with certain health conditions, health-care workers, and close contacts of persons at high risk for complications from influenza). Analyses of influenza vaccination coverage for the 2004-05 influenza season indicated that coverage levels for adults in priority groups nearly reached the levels of previous years, whereas coverage levels among adults not in priority groups were approximately half the levels of the 2003-04 season. These findings suggested that national public health actions to direct available vaccine supply to persons at high risk for complications from influenza during the supply disruption were successful. To assess influenza vaccination coverage among persons aged 50-64 years for the 2004-05 influenza season relative to the 2003-04 season and to estimate the effect of shortages on selected subgroups, the National Committee for Quality Assurance (NCQA) analyzed data from a survey of persons enrolled in commercial managed care health plans. This report summarizes the findings of that analysis, which indicated that, although vaccination coverage declined substantially from 2003-04 to 2004-05 among all subgroups in this age range, respondents who were older or who reported poorer health status exhibited smaller relative declines in vaccination coverage between the two seasons.     

Influenza vaccination coverage among persons with asthma--United States, 2005-06 influenza season

During 2006, approximately 6.8 million (9.3%) U.S. children and 16.1 million (7.3%) U.S. adults were reported to have asthma. Since 1964, the Advisory Committee on Immunization Practices (ACIP) has recommended influenza vaccination of all persons with asthma because of the higher risk for medical complications from influenza for those persons. Influenza vaccination coverage of persons with asthma varies by age group and remains below Healthy People 2010 targets of 60% coverage of persons aged 18--64 years with high-risk conditions (14-29 c) and 90% of all persons aged > or =65 years (14-29 a). Influenza vaccination rates of children and older adults with asthma have not been well studied. Using 2006 National Health Interview Survey (NHIS) data, this report provides the first examination of influenza vaccination rates and related factors across a national sample of persons with asthma aged > or =2 years. The results indicated that 36.2% received influenza vaccination during the 2005--06 influenza season. Vaccination rates remained below target levels among all subgroups examined, including those reporting the greatest number of health-care visits in the past 12 months. The results of this study indicate that influenza vaccination coverage of all persons with asthma can be improved by increasing access to health care and using opportunities for vaccination during health-care visits.     

Influenza vaccination coverage among children with asthma--United States, 2004-05 influenza season

In 2005, approximately 8.9% (6.5 million) of U.S. children aged <18 years were reported to have current asthma. Children with asthma are at high risk for complications from influenza, and influenza vaccination has been determined to safely and effectively reduce rates of influenza in these children. Since its establishment in 1964, the Advisory Committee on Immunization Practices (ACIP) has recommended that all children with asthma aged > or =6 months receive vaccination with inactivated influenza vaccine during each influenza season; however, national influenza vaccination coverage rates specifically for children with asthma have not been determined. Previous studies have assessed influenza vaccination rates in children with asthma at the local level using health maintenance organization and clinician group-practice information, with estimates ranging from 10% to 43% for various influenza seasons. Another study used Behavioral Risk Factor Surveillance System (BRFSS) data to estimate influenza vaccination coverage in children aged 2-17 years with one or more conditions putting them at high risk for complications from influenza (including asthma, although asthma was not assessed separately); in that study, the national rate was estimated at 34.8% for the 2004-05 influenza season (based on a sample size of 685, which included all states and the District of Columbia [DC]). To estimate national influenza vaccination coverage rates among children aged 2-17 years with current asthma, CDC analyzed data from the 2005 National Health Interview Survey (NHIS). This report describes the results of that analysis and provides the first national estimates of influenza vaccination coverage among children with asthma. The findings indicated that although children with current asthma were more likely to receive influenza vaccination than children without current asthma, the vaccination coverage rate among children with asthma was low, at 29.0% (95% confidence interval [CI] = 24.5-33.9). These findings underscore the need to increase influenza vaccination coverage in children with asthma aged 2-17 years by identifying and overcoming barriers to vaccination.     

Influenza vaccination in pregnancy: practices among obstetrician-gynecologists--United States, 2003-04 influenza season

Women infected with influenza virus during pregnancy are at increased risk for serious complications and hospitalization. During 1997-2003, the Advisory Committee on Immunization Practices (ACIP) included healthy pregnant women who would be in their second or third trimester of pregnancy during the influenza season among those persons at high risk for whom influenza vaccination was indicated. Also included were women at any stage of pregnancy with certain chronic medical conditions, such as asthma, diabetes mellitus, or heart disease. ACIP emphasized that the influenza vaccine was safe for breastfeeding mothers and their infants and that household contacts of children aged <2 years also should be vaccinated. However, despite these recommendations, only 13% of pregnant women received influenza vaccination in 2003. To assess understanding of the ACIP recommendations among obstetrician-gynecologists (OB/GYNs), the American College of Obstetricians and Gynecologists (ACOG), with support from CDC, surveyed a national sample of OB/GYNs in May 2004. This report describes the results of that survey, which indicated that 52% of OB/GYNs surveyed would recommend influenza vaccination for a healthy woman in the first trimester of pregnancy, 95% would recommend the vaccine for a healthy pregnant woman beyond the first trimester, and 63% would recommend vaccination for a woman with a medical condition in the first trimester. However, of the physicians who would recommend vaccination, 36%-38% reported that influenza vaccination was not offered in their practices. Increased efforts are needed to improve vaccine availability and to educate OB/GYNs regarding the updated ACIP recommendations on the use of influenza vaccine in the first trimester for both healthy pregnant women and pregnant women at high risk.     

Influenza vaccination coverage among health-care personnel --- United States, 2010-11 influenza season

The Advisory Committee on Immunization Practices (ACIP) and the Healthcare Infection Control Practices Advisory Committee recommend that all U.S. health-care personnel (HCP) be vaccinated annually against influenza. Nonetheless, influenza vaccination coverage among HCP in the United States has increased slowly over the past decade; during the 2009-10 influenza season, 61.9% of HCP received seasonal influenza vaccination. To update data with estimates from the 2010-11 influenza season, CDC conducted an Internet-based survey of 1,931 HCP who participated in three online survey panels. This report summarizes the results of that survey, which indicated that overall influenza vaccination coverage among HCP was 63.5% during the 2010--11 influenza season, similar to coverage for the 2009-10 season. Among HCP who reported working at a facility where vaccination was required by their employer, 98.1% were vaccinated. Among HCP without such an employer requirement but who were offered vaccination onsite, greater coverage was associated with a personal reminder from the employer to get vaccinated (69.9%), vaccination availability at no cost (67.9%), and vaccination availability for >1 day (68.8%). Influenza vaccination of HCP is needed to protect patients from HCP-transmitted disease. Maximizing influenza vaccination for all HCP is an important part of any comprehensive infection-control program.     

Influenza vaccination coverage among pregnant women --- United States, 2010-11 influenza season

Women are at increased risk for morbidity and mortality from influenza during pregnancy. Vaccinating pregnant women for influenza can protect both the women and their infants, especially infants aged <6 months who are not old enough to receive influenza vaccination. Since 2004, the Advisory Committee on Immunization Practices and the American College of Obstetricians and Gynecologists have recommended inactivated influenza vaccine for all women who are pregnant during influenza season, regardless of trimester. Before 2009, estimated influenza vaccination coverage among pregnant women had been consistently low (approximately 15%). However, vaccination levels increased substantially in response to the 2009 influenza A (H1N1) pandemic to nearly 50%. To estimate influenza vaccination coverage among pregnant women for the 2010-11 season, CDC analyzed data from an Internet panel survey conducted in April 2011 among women who were pregnant any time during October 2010-January 2011. Among 1,457 survey respondents, 49% reported that they had received influenza vaccination: 12% were vaccinated before pregnancy, 32% during pregnancy, and 5% after pregnancy. Women offered influenza vaccination by a health-care provider (62%) were more likely to be vaccinated (71%) than other women (14%) and were more likely to have positive attitudes about vaccine effectiveness and safety. These results indicate that the higher vaccination level achieved the previous season (2009-10) was sustained and emphasize the critical role of health-care providers in promoting influenza vaccination. Continued efforts are needed to encourage health-care providers to strongly recommend and offer influenza vaccination to pregnant patients to protect both the mothers and their infants.     

Update: influenza activity United States, 2004-05 season

Influenza activity has increased steadily in the United States since late December and, as of February 19, might not have peaked. Laboratory-confirmed influenza infections have been reported from all 50 states. This report summarizes influenza activity during October 3, 2004-February 19, 2005.     

Update: influenza activity--United States and worldwide, 2003-04 season, and composition of the 2004-05 influenza vaccine

During the 2003-04 influenza season, influenza A (H1), A (H3N2), and B viruses co-circulated worldwide, and influenza A (H3N2) viruses predominated. Several Asian countries reported widespread outbreaks of avian influenza A (H5N1) among poultry. In Vietnam and Thailand, these outbreaks were associated with severe illnesses and deaths among humans. In the United States, the 2003-04 influenza season began earlier than most seasons, peaked in December, was moderately severe in terms of its impact on mortality, and was associated predominantly with influenza A (H3N2) viruses. This report 1) summarizes information collected by World Health Organization (WHO) and National Respiratory and Enteric Virus Surveillance System (NREVSS) collaborating laboratories, state and local health departments, health-care providers, vital statistics registries, and CDC and 2) describes influenza activity in the United States and worldwide during the 2003-04 influenza season and the composition of the 2004-05 influenza vaccine.     

Effectiveness of the 2003-2004 influenza vaccine among U.S. military basic trainees: a year of suboptimal match between vaccine and circulating strain

Effectiveness of the 2003-2004 influenza vaccine was evaluated at five military basic training centers throughout the United States. Data from surveillance conducted in December and January 2003-2004 in this highly vaccinated population were evaluated. During this period, 10.6% (37/350) of specimens were positive for influenza A. A 14-day period after vaccination was considered the period prior to immune protection; vaccine effectiveness (VE) was calculated based on febrile respiratory illness presentation and laboratory confirmation of influenza before or after this 14-day period. Thirty-two cases presented within 14 days of vaccination, and five cases presented beyond 14 days from vaccination. VE in this population was estimated to be 94.4% for laboratory-confirmed influenza. In contrast, VE was only 13.9% for influenza-like illness (ILI) without a laboratory confirmation.     

Influenza vaccine effectiveness among US military basic trainees, 2005-06 season

Virtually all US military basic trainees receive seasonal influenza vaccine. Surveillance data collected from December 2005 through March 2006 were evaluated to estimate effectiveness of the influenza vaccine at 6 US military basic training centers. Vaccine effectiveness against laboratory-confirmed influenza was 92% (95% confidence interval 85%-96%).     

Influenza vaccine uptake in adults aged 50-64 years: policy and practice in England 2003/2004

A small national study was carried out in England in 2003/2004 to ascertain the views of primary care trusts (PCTs) and general practitioners (GPs) on whether influenza immunisation should be extended to all people aged 50-64 years from the current recommendation of 65 years or more. Results showed that as many primary care trusts would be in favour, as would not be in favour. A similarly divided view was expressed by general practitioners. Vaccine uptake rates for high-risk (HR) and low-risk (LR) adults aged 50-64 years in the study population were higher in those practices where the GP was in favour of a more inclusive policy of offering flu vaccine to all persons aged 50 years or more, compared with those that did not favour this policy (60% versus 54% HR (p=0.02) and 16% versus 11% LR (p=0.02)). Higher rates of vaccine uptake for low-risk patients aged 50-64 years were also reported from practices where GPs perceived a greater health benefit of immunisation for this age group. Although policy for recommending vaccine to all patients aged 50 years or more is established elsewhere, opinion on whether such a policy should be adopted in England is currently divided amongst those providing local health services.     

Place of influenza vaccination among adults --- United States, 2010-11 influenza season

The 2010-11 influenza season was the first season after the 2009 influenza A (H1N1) pandemic and the first season that the Advisory Committee on Immunization Practices (ACIP) recommended influenza vaccination for all persons aged ≥6 months (1). During the pandemic, many new partnerships between public health agencies and medical and nonmedical vaccination providers were formed, increasing the number of vaccination providers (2). To provide a baseline for places where adults received influenza vaccination since the new ACIP recommendation and to help vaccination providers plan for the 2011-12 influenza season, CDC analyzed information from 46 states and the District of Columbia (DC) on influenza vaccination of adults aged ≥18 years for the 2010-11 season, collected during January-March 2011 by the Behavioral Risk Factor Surveillance System (BRFSS). This report summarizes the results of that analysis, which found that, for adults overall, a doctor's office was the most common place (39.8%) for receipt of the 2010-11 influenza vaccine, with stores (e.g., supermarkets or drug stores) (18.4%) and workplaces (17.4%) the next most common. For those aged 18-49 years and 50-64 years, a workplace was the second most common place of vaccination (25.7% and 21.1%, respectively). Persons aged ≥65 years who were not vaccinated at a doctor's office were most likely (24.3%) to have been vaccinated at a store. The results indicate that both medical and nonmedical settings are common places for adults to receive influenza vaccinations, that a doctor's office is the most important medical setting, and that workplaces and stores are important nonmedical settings.     

Experiences with obtaining influenza vaccination among persons in priority groups during a vaccine shortage--United States, October-November, 2004

After the announcement that the supply of inactivated influenza vaccine available to the U.S. public for the 2004-05 influenza season would be reduced by approximately one half, the Advisory Committee on Immunization Practices (ACIP) recommended that the remaining vaccine supply should be reserved for 1) certain groups of persons at high risk for serious health problems from influenza, 2) health-care workers involved in direct patient care, and 3) close contacts of children aged <6 months. To determine what proportion of persons at increased risk for influenza complications had been vaccinated as of the day of the survey, what proportion sought vaccination but did not receive it because of the shortage, and what factors might be dissuading persons at high risk from seeking influenza vaccination, Harvard School of Public Health (HSPH), in collaboration with International Communications Research, conducted a national survey. This report summarizes the results of that survey, which indicated that approximately 63% of persons aged > or =65 years and 46% of chronically ill adults who tried to get the influenza vaccine were able to do so. More than half of adults at high risk did not try to get the influenza vaccine. Because available supplies of inactivated influenza vaccine are targeted to high-risk groups, persons in these groups should continue to pursue vaccination.     

Inactivated influenza vaccine effectiveness in children under 6 years of age during the 2002-2003 season

This study was carried out to investigate the effectiveness of influenza vaccine among 2913 children (1512 vaccinees and 1401 nonvaccinees) under 6 years of age during the 2002-2003 season. Study subjects were recruited from 54 paediatric clinics, located in eight areas in Japan. Maximum body temperatures were obtained weekly from parents between 2002 December 16 and 2003 April 13. Influenza-like illness (ILI) was defined as an acute febrile illness (> or =38.0 degrees C) during the peak epidemic period in each study area. The vaccine antigens included were A/New Caledonia/20/99(H1N1), A/Panama/2007/99(H3N2) and B/Shandong/7/97. Vaccine effectiveness was analyzed by comparing the frequencies of ILI between vaccinees and nonvaccinees. The adjusted odds ratio (OR) and its 95% confidence interval (95% CI) were calculated by the proportional odds model using logistic regression with three-level outcome variables (<38.0/38.0-38.9/> or =39.0 degrees C). A significantly decreased OR of vaccination was observed (OR: 0.76; 95% CI: 0.66-0.88), corresponding to a vaccine effectiveness (1-OR) of 24% (95% CI: 12%-34%). When the analysis was confined to those aged > or =2 years, a more pronounced OR (0.67, 0.56-0.79) was obtained with a vaccine effectiveness of 33% (21%-44%). On the other hand, no significant vaccine effectiveness was detected among very young children; the ORs were 1.84 (0.81-4.19) for those <1 year of age and 0.99 (0.72-1.36) for those 1.0-1.9 years of age and 1.07 (0.80-1.44) when these two age groups were combined. Thus, among very young children vaccine effectiveness could not be demonstrated.     

Influenza vaccination levels among persons aged > or =65 years and among persons aged 18-64 years with high-risk conditions--United States, 2003

Influenza vaccination is an effective tool for preventing hospitalization and death among persons aged > or =65 years and among persons aged 18-64 years with medical conditions that increase the risk for influenza-related complications. Two national health objectives for 2010 are to increase influenza vaccination coverage to 90% among persons aged > or =65 years and to 60% among persons aged 18-64 years who have one or more high-risk conditions (objectives 14-29a and 14-29c, respectively). To determine influenza vaccination coverage among persons in both targeted groups, CDC analyzed data from the 2003 National Health Interview Survey (NHIS). This report summarizes the results of that analysis, which determined that influenza vaccination coverage among persons aged > or =65 years and persons aged 18-64 years with high-risk conditions remains substantially below 2010 target levels. In addition, racial/ethnic disparities in coverage levels persist in both targeted populations. To improve overall influenza vaccination coverage and reduce racial/ethnic disparities, combinations of evidence-based effective interventions should be implemented, and the influenza vaccine supply should be stabilized.     

Influenza vaccination coverage among children aged 6-23 months--United States, 2005-06 influenza season

Children aged <2 years are at increased risk for influenza-related hospitalizations, and those aged <5 years have more influenza-related health-care visits than older children. In 2004, the Advisory Committee on Immunization Practices (ACIP) recommended annual influenza vaccination of children aged 6-23 months. Two doses, at least 4 weeks apart, were recommended to fully vaccinate children aged <9 years who were receiving influenza vaccination for the first time. To assess influenza vaccination coverage among children aged 6-23 months during the 2005-06 influenza season, data from the 2006 National Immunization Survey (NIS) were analyzed. This report describes the results of that analysis, which indicated that 31.9% of children in this age group received at least 1 dose of influenza vaccine and 20.6% were fully vaccinated according to ACIP recommendations; however, results varied substantially among states. The results underscore the need to continue to monitor influenza vaccination coverage among young children, develop systems to provide childhood influenza vaccination services more efficiently, and increase awareness among health-care providers and caregivers about the effectiveness of influenza vaccination among young children.     

Influenza vaccination coverage among children aged 6-23 months--United States, 2006-07 influenza season

Children aged <5 years have more influenza-related medical-care visits compared with older children, and those aged <2 years are at the greatest risk for influenza-related hospitalizations. In 2002, the Advisory Committee on Immunization Practices (ACIP) encouraged annual influenza vaccination of children aged 6-23 months and then, in 2004, recommended vaccination for this group. Two doses, spaced at least 4 weeks apart, are recommended to fully vaccinate children aged <9 years who are receiving influenza vaccination for the first time. This report, based on data from the 2007 National Immunization Survey (NIS), provides an assessment of influenza vaccination coverage among children aged 6-23 months during September-December of the 2006-07 influenza season. Nationally, 31.8% of children received 1 or more doses of influenza vaccine, and 21.3% were fully vaccinated, with substantial variability among states. The findings underscore the need to increase interest in and access to influenza vaccination for more children in the United States. Further study is needed to identify knowledge deficits or logistical barriers that might contribute to continued low influenza vaccination coverage among young children.     

Update: influenza activity - United States, 2011-12 season and composition of the 2012-13 influenza vaccine

During the 2011-12 influenza season in the United States, influenza activity* occurred at low levels during October through December and increased in January and February before peaking in mid-March. Influenza A (H3N2) viruses predominated overall, but influenza A (H1N1)pdm09 (pH1N1) and influenza B viruses also circulated widely. This influenza season was mild compared with recent years, with a lower percentage of outpatient visits for influenza-like illness (ILI),? lower rates of hospitalizations, and fewer deaths attributed to pneumonia and influenza. This report summarizes influenza activity in the United States during the 2011-12 influenza season (October 2, 2011-May 19, 2012) and reports the recommendations for the components of the 2012-13 Northern Hemisphere influenza vaccine.     

Update: influenza activity--United States and worldwide, 2002-03 season,and composition of the 2003-04 influenza vaccine

In collaboration with the World Health Organization (WHO), its collaborating laboratories, state and local health departments, health-care providers, and vital statistic registries, CDC conducts surveillance to monitor influenza activity and to detect antigenic changes in the circulating strains of influenza viruses. During the 2002-03 influenza season, influenza A (H1), A (H3N2), and B viruses co-circulated in the Northern Hemisphere. Human infections with avian influenza A (H5N1) and A (H7N7) viruses were reported in Hong Kong and the Netherlands, respectively. In the United States, the 2002-03 influenza season was mild; influenza A (H1) and B viruses circulated widely, and the predominant virus varied by region and time of season. This report summarizes influenza activity in the United States and worldwide during the 2002-03 influenza season and describes the composition of the 2003-04 influenza vaccine.