All-Cause Mortality during First Wave of Pandemic (H1N1) 2009, New South Wales, Australia, 2009

In temperate countries, death rates increase in winter, but influenza epidemics often cause greater increases. The death rate time series that occurs without epidemic influenza can be called a seasonal baseline. Differentiating observed death rates from the seasonally oscillating baseline provides estimated influenza-associated death rates. During 2003–2009 in New South Wales, Australia, we used a Serfling approach with robust regression to estimate age-specific weekly baseline all-cause death rates. Total differences between weekly observed and baseline rates during May–September provided annual estimates of influenza-associated death rates. In 2009, which included our first wave of pandemic (H1N1) 2009, the all-age death rate was 6.0 (95% confidence interval 3.1–8.9) per 100,000 persons lower than baseline. In persons >80 years of age, it was 131.6 (95% confidence interval 126.2–137.1) per 100,000 lower. This estimate is consistent with a pandemic virus causing mild illness in most persons infected and sparing older persons.     

Age as Risk Factor for Death from Pandemic (H1N1) 2009, Chile

Pandemic (H1N1) 2009 affected Chile during the winter of 2009. The hospitalization rate was 0.56% overall and 3.47% for persons >60 years of age at risk for severe disease and death independent of concurrent conditions. Age >60 years was the major risk factor for death from pandemic (H1N1) 2009.     

Household Transmission of Pandemic (H1N1) 2009, San Antonio, Texas, USA, April�CMay 2009

To assess household transmission of pandemic (H1N1) 2009 in San Antonio, Texas, USA, during April 15–May 8, 2009, we investigated 77 households. The index case-patient was defined as the household member with the earliest onset date of symptoms of acute respiratory infection (ARI), influenza-like illness (ILI), or laboratory-confirmed pandemic (H1N1) 2009. Median interval between illness onset in index and secondary case-patients was 4 days (range 1–9 days); the index case-patient was likely to be <18 years of age (p = 0.034). The secondary attack rate was 4% for pandemic (H1N1) 2009, 9% for ILI, and 13% for ARI. The secondary attack rate was highest for children <5 years of age (8%–19%) and lowest for adults >50 years of age (4%–12%). Early in the outbreak, household transmission primarily occurred from children to other household members and was lower than the transmission rate for seasonal influenza.     

Epidemiology of Influenza-like Illness during Pandemic (H1N1) 2009, New South Wales, Australia

To rapidly describe the epidemiology of influenza-like illness (ILI) during the 2009 winter epidemic of pandemic (H1N1) 2009 virus in New South Wales, Australia, we used results of a continuous population health survey. During July–September 2009, ILI was experienced by 23% of the population. Among these persons, 51% were unable to undertake normal duties for <3 days, 55% sought care at a general practice, and 5% went to a hospital. Factors independently associated with ILI were younger age, daily smoking, and obesity. Effectiveness of prepandemic seasonal vaccine was ≈20%. The high prevalence of risk factors associated with a substantially increased risk for ILI deserves greater recognition.     

Effectiveness of Seasonal Influenza Vaccine against Pandemic (H1N1) 2009 Virus, Australia, 2010

To estimate effectiveness of seasonal trivalent and monovalent influenza vaccines against pandemic influenza A (H1N1) 2009 virus, we conducted a test-negative case–control study in Victoria, Australia, in 2010. Patients seen for influenza-like illness by general practitioners in a sentinel surveillance network during 2010 were tested for influenza; vaccination status was recorded. Case-patients had positive PCRs for pandemic (H1N1) 2009 virus, and controls had negative influenza test results. Of 319 eligible patients, test results for 139 (44%) were pandemic (H1N1) 2009 virus positive. Adjusted effectiveness of seasonal vaccine against pandemic (H1N1) 2009 virus was 79% (95% confidence interval 33%–93%); effectiveness of monovalent vaccine was 47% and not statistically significant. Vaccine effectiveness was higher among adults. Despite some limitations, this study indicates that the first seasonal trivalent influenza vaccine to include the pandemic (H1N1) 2009 virus strain provided significant protection against laboratory-confirmed pandemic (H1N1) 2009 infection.After the emergence and rapid global spread of pandemic influenza A (H1N1) 2009 virus, development of a pandemic (H1N1) 2009–specific vaccine began (1). A candidate reassortant vaccine virus, derived from the A/California/7/2009 (H1N1)v virus as recommended by the World Health Organization, was used to produce a monovalent, unadjuvanted, inactivated, split-virus vaccine for Australia (2,3). The national monovalent pandemic (H1N1) 2009 vaccination program in Australia ran from September 30, 2009, through December 31, 2010, and vaccination was publicly funded for all persons in Australia >6 months of age (4,5).In September 2009, the World Health Organization recommended that trivalent influenza vaccines for use in the 2010 influenza season (Southern Hemisphere winter) contain A/California/7/2009 (H1N1)–like virus, A/Perth/16/2009 (H3N2)–like virus, and B/Brisbane/60/2008 (of the B/Victoria/2/87 lineage) virus (6). Since March 2010, the Australian Government has provided free seasonal influenza vaccination to all Australia residents >65 years of age, all Aboriginal and Torres Strait Islander persons >50 years, all Aboriginal and Torres Strait Islander persons 15–49 years with medical risk factors, persons >6 months with conditions that predispose them to severe influenza, and pregnant women (7). Influenza vaccination is also recommended, but not funded, for persons who might transmit influenza to those at high risk for complications from influenza, persons who provide essential services, travelers, and anyone >6 months of age for whom reducing the likelihood of becoming ill with influenza is desired. Individual industries are also advised to consider the benefits of offering influenza vaccine in the workplace (8). Because pandemic (H1N1) 2009 was expected to be the dominant strain in 2010, the monovalent vaccine continued to be used despite the availability of the seasonal vaccine, particularly by persons who were not eligible for funded vaccine (M. Batchelor, pers. comm.). However, in 2010, there were no published data on the relative use of monovalent and seasonal vaccines at that time.The need for rapid implementation of programs results in initial studies using immunogenicity, rather than efficacy, to assess performance of influenza vaccines. After 1 dose of monovalent pandemic (H1N1) 2009 vaccine containing 15 µg hemagglutinin without adjuvant, seroprotection was estimated to be 94%–97% in working-age adults (3,9,10) and 75% in children (10). Observational studies provide a practical way to calculate vaccine effectiveness under field conditions (11,12). Effectiveness of monovalent pandemic (H1N1) 2009 was estimated to be 72%–97% by 3 studies in general practice and community-based settings in Europe (13–15), 90% in a hospital-based study in Spain (16), and 100% in a community-based study of children in Canada (17). These studies were conducted in populations for which the respective local or national pandemic vaccination program primarily used vaccine without adjuvant.We assessed effectiveness of the 2010 seasonal influenza vaccine against laboratory-confirmed pandemic (H1N1) 2009 influenza infection in Victoria, Australia. Data came from an established test-negative case–control study in a general practitioner sentinel surveillance network (18,19).     

Risk Factors for Pandemic (H1N1) 2009 Virus Seroconversion among Hospital Staff, Singapore

We describe incidence and risk factors for pandemic (H1N1) 2009 virus infection in healthcare personnel during the June–September 2009 epidemic in Singapore. Personnel contributed 3 serologic samples during June–October 2009, with seroconversion defined as a >4-fold increase in hemagglutination inhibition titers to pandemic (H1N1) 2009. Of 531 participants, 35 showed evidence of seroconversion. Seroconversion rates were highest in nurses (28/290) and lowest in allied health staff (2/116). Significant risk factors on multivariate analysis were being a nurse (adjusted odds ratio [aOR] 4.5, 95% confidence interval [CI] 1.0–19.6) and working in pandemic (H1N1) 2009 isolation wards (aOR 4.5, 95% CI 1.3–15.6). Contact with pandemic (H1N1) 2009–infected colleagues (aOR 2.5, 95% CI 0.9–6.6) and larger household size (aOR 1.2, 95% CI 1.0–1.4) were of borderline significance. Our study suggests that seroconversion was associated with occupational and nonoccupational risk factors.     

Oseltamivir Resistance in Adult Oncology and Hematology Patients Infected with Pandemic (H1N1) 2009 Virus, Australia

We describe laboratory-confirmed influenza A pandemic (H1N1) 2009 in 17 hospitalized recipients of a hematopoietic stem cell transplant (HSCT) (8 allogeneic) and in 15 patients with malignancy treated at 6 Australian tertiary centers during winter 2009. Ten (31.3%) patients were admitted to intensive care, and 9 of them were HSCT recipients. All recipients of allogeneic HSCT with infection <100 days posttransplantation or severe graft-versus-host disease were admitted to an intensive care unit. In-hospital mortality rate was 21.9% (7/32). The H275Y neuraminidase mutation, which confers oseltamivir resistance developed in 4 of 7 patients with PCR positive for influenza after >4 days of oseltamivir therapy. Three of these 4 patients were critically ill. Oseltamivir resistance in 4 (13.3%) of 30 patients who were administered oseltamivir highlights the need for ongoing surveillance of such resistance and further research on optimal antiviral therapy in the immunocompromised.     

Household Responses to Pandemic (H1N1) 2009�Crelated School Closures, Perth, Western Australia

School closure is often purported to reduce influenza transmission, but little is known about its effect on families. We surveyed families affected by pandemic (H1N1) 2009–related school closures in Perth, Western Australia, Australia. Surveys were returned for 233 (58%) of 402 students. School closure was deemed appropriate by 110 parents (47%); however, 91 (45%) parents of 202 asymptomatic students reported taking >1 day off work to care for their child, and 71 (35%) had to make childcare arrangements because of the class closures. During the week, 172 (74%) students participated in activities outside the home on >1 occasion, resulting in an average of 3.7 out-of-home activities for each student. In our survey, activities outside the home were commonly reported by students affected by school closure, the effect on families was substantial, and parental opinion regarding school closures as a means to mitigate the outbreak of pandemic (H1N1) 2009 was divided.     

Deaths Associated with Respiratory Syncytial and Influenza Viruses among Persons ≥5 Years of Age in HIV-Prevalent Area,South Africa, 1998–20091

We estimated deaths attributable to influenza and respiratory syncytial virus (RSV) among persons >5 years of age in South Africa during 1998–2009 by applying regression models to monthly deaths and laboratory surveillance data. Rates were expressed per 100,000 person-years. The mean annual number of seasonal influenza–associated deaths was 9,093 (rate 21.6). Persons >65 years of age and HIV-positive persons accounted for 50% (n = 4,552) and 28% (n = 2,564) of overall seasonal influenza-associated deaths, respectively. In 2009, we estimated 4,113 (rate 9.2) influenza A(H1N1)pdm09–associated deaths. The mean of annual RSV-associated deaths during the study period was 511 (rate 1.2); no RSV-associated deaths were estimated in persons >45 years of age. Our findings support the recommendation for influenza vaccination of older persons and HIV-positive persons. Surveillance for RSV should be strengthened to clarify the public health implications and severity of illness associated with RSV infection in South Africa.     

Seasonal and Pandemic A (H1N1) 2009 influenza vaccination coverage and attitudes among health-care workers in a Spanish University Hospital

Influenza vaccination coverage among health-care workers (HCWs) remains the lowest compared with other priority groups for immunization. Little is known about the acceptability and compliance with the pandemic (H1N1) 2009 influenza vaccine among HCWs during the current campaign. Between 23 December 2009 and 13 January 2010, once the workplace vaccination program was over, we conducted a cross-sectional, questionnaire-based survey at the University Hospital 12 de Octubre (Madrid, Spain). Five hundred twenty-seven HCWs were asked about their influenza immunization history during the 2009–2010 season, as well as the reasons for accepting or declining either the seasonal or pandemic vaccines. Multiple logistic-regression analysis was preformed to identify variables associated with immunization acceptance. A total of 262 HCWs (49.7%) reported having received the seasonal vaccine, while only 87 (16.5%) affirmed having received the pandemic influenza (H1N1) 2009 vaccine. “Self-protection” and “protection of the patient” were the most frequently adduced reasons for acceptance of the pandemic vaccination, whereas the existence of “doubts about vaccine efficacy” and “fear of adverse reactions” were the main arguments for refusal. Simultaneous receipt of the seasonal vaccine (odds ratio [OR]: 0.27; 95% confidence interval [95% CI]: 0.14–0.52) and being a staff (OR: 0.08; 95% CI: 0.04–0.19) or a resident physician (OR: 0.16; 95% CI: 0.05–0.50) emerged as independent predictors for pandemic vaccine acceptance, whereas self-reported membership of a priority group was associated with refusal (OR: 5.98; 95% CI: 1.35–26.5). The pandemic (H1N1) 2009 influenza vaccination coverage among the HCWs in our institution was very low (16.5%), suggesting the role of specific attitudinal barriers and misconceptions about immunization in a global pandemic scenario.     

Increased extent of and risk factors for pandemic (H1N1) 2009 and seasonal influenza among children, Israel

During the pandemic (H1N1) 2009 outbreak in Israel, incidence rates among children were 2× higher than that of the previous 4 influenza seasons; hospitalization rates were 5× higher. Children hospitalized for pandemic (H1N1) 2009 were older and had more underlying chronic diseases than those hospitalized for seasonal influenza.     

Pandemic (H1N1) 2009 and Seasonal Influenza A (H1N1) Co-infection, New Zealand, 2009

Co-infection with seasonal influenza A (H1N1) and pandemic (H1N1) 2009 could result in reassortant viruses that may acquire new characteristics of transmission, virulence, and oseltamivir susceptibility. Results from oseltamivir-sensitivity testing on viral culture suggested the possibility of co-infections with oseltamivir-resistant (seasonal A [H1N1]) and -susceptible (pandemic [H1N1] 2009) viruses.     

Influenza pandemic (H1N1) 2009 activity during summer 2009. Effectiveness of the 2008-9 trivalent vaccine against pandemic influenza in Spain

Introduction

The Spanish influenza surveillance system (SISS) maintained its activity during the summer of 2009 to monitor the influenza pandemic.

Objectives

To describe pandemic influenza activity from May to September 2009 and to estimate the effectiveness of the 2008-9 seasonal influenza vaccine against laboratory-confirmed pandemic (H1N1) 2009 influenza.

Methods

Data from the SISS were used to identify the trend of pandemic (H1N1) 2009 influenza outside the influenza season. For the effectiveness study, we compared the vaccination status of notified cases [influenza-like illnesses (ILI) laboratory confirmed as pandemic influenza] with that of the test-negative controls.

Results

The first laboratory-confirmed case of the pandemic virus was notified in the system in week 20/2009. The ILI rate increased gradually in the study period, exceeding basic activity in week 38. The proportion of pandemic (H1N1) 2009 influenza viruses detected by the system represented 14% in week 20/2009 and rapidly increased to 90% in week 34. The adjusted vaccine effectiveness of the 2008-9 seasonal vaccine against laboratory-confirmed pandemic influenza was 12% (-30; 41).

Conclusions

The SISS became an essential tool for pandemic monitoring in Spain. The improved SISS will provide more accurate information on influenza activity in future seasonal or pandemic waves. Using surveillance data, we could not demonstrate the effectiveness of the seasonal 2008-9 vaccine against laboratory-confirmed pandemic influenza.     

Pandemic (H1N1) 2009 Virus on Commercial Swine Farm, Thailand

A swine influenza outbreak occurred on a commercial pig farm in Thailand. Outbreak investigation indicated that pigs were co-infected with pandemic (H1N1) 2009 virus and seasonal influenza (H1N1) viruses. No evidence of gene reassortment or pig-to-human transmission of pandemic (H1N1) 2009 virus was found during the outbreak.     

Swine influenza virus antibodies in humans, western Europe, 2009

Serologic studies for swine influenza viruses (SIVs) in humans with occupational exposure to swine have been reported from the Americas but not from Europe. We compared levels of neutralizing antibodies against 3 influenza viruses--pandemic (H1N1) 2009, an avian-like enzootic subtype H1N1 SIV, and a 2007-08 seasonal subtype H1N1--in 211 persons with swine contact and 224 matched controls in Luxembourg. Persons whose profession involved contact with swine had more neutralizing antibodies against SIV and pandemic (H1N1) 2009 virus than did the controls. Controls also had antibodies against these viruses although exposure to them was unlikely. Antibodies against SIV and pandemic (H1N1) 2009 virus correlated with each other but not with seasonal subtype H1N1 virus. Sequential exposure to variants of seasonal influenza (H1N1) viruses may have increased chances for serologic cross-reactivity with antigenically distinct viruses. Further studies are needed to determine the extent to which serologic responses correlate with infection.     

Pandemic (H1N1) 2009 Surveillance and Prevalence of Seasonal Influenza, Singapore

On April 25, 2009, Singapore implemented strict containment measures for pandemic (H1N1) 2009 with enhanced surveillance and hospital isolation. In the first month, seasonal influenza, predominantly virus subtype H3N2, was diagnosed for 32% of patients with acute febrile respiratory illness. Our findings underscore the high prevalence of seasonal influenza in Singapore.     

Zoonotic Transmission of Avian Influenza Virus (H5N1), Egypt, 2006�C2009

During March 2006–March 2009, a total of 6,355 suspected cases of avian influenza (H5N1) were reported to the Ministry of Health in Egypt. Sixty-three (1%) patients had confirmed infections; 24 (38%) died. Risk factors for death included female sex, age >15 years, and receiving the first dose of oseltamivir >2 days after illness onset. All but 2 case-patients reported exposure to domestic poultry probably infected with avian influenza virus (H5N1). No cases of human-to-human transmission were found. Greatest risks for infection and death were reported among women >15 years of age, who accounted for 38% of infections and 83% of deaths. The lower case-fatality rate in Egypt could be caused by a less virulent virus clade. However, the lower mortality rate seems to be caused by the large number of infected children who were identified early, received prompt treatment, and had less severe clinical disease.