Household Responses to Pandemic (H1N1) 2009–related School Closures, Perth, Western Australia

Results from closures will determine the appropriateness and efficacy of this mitigation measure

Pandemic (H1N1) 2009 influenza community transmission was established in one Australian state when the virus was first identified in North America

BACKGROUND In mid-June 2009 the State of Victoria in Australia appeared to have the highest notification rate of pandemic (H1N1) 2009 influenza in the world. We hypothesise that this was because community transmission of pandemic influenza was already well established in Victoria at the time testing for the novel virus commenced. In contrast, this was not true for the pandemic in other parts of Australia, including Western Australia (WA). METHODS We used data from detailed case follow-up of patients with confirmed infection in Victoria and WA to demonstrate the difference in the pandemic curve in two Australian states on opposite sides of the continent. We modelled the pandemic in both states, using a susceptible-infected-removed model with Bayesian inference accounting for imported cases. RESULTS Epidemic transmission occurred earlier in Victoria and later in WA. Only 5% of the first 100 Victorian cases were not locally acquired and three of these were brothers in one family. By contrast, 53% of the first 102 cases in WA were associated with importation from Victoria. Using plausible model input data, estimation of the effective reproductive number for the Victorian epidemic required us to invoke an earlier date for commencement of transmission to explain the observed data. This was not required in modelling the epidemic in WA. CONCLUSION Strong circumstantial evidence, supported by modelling, suggests community transmission of pandemic influenza was well established in Victoria, but not in WA, at the time testing for the novel virus commenced in Australia. The virus is likely to have entered Victoria and already become established around the time it was first identified in the US and Mexico

Comparison of Pandemic (H1N1) 2009 and Seasonal Influenza, Western Australia, 2009

TOC summary: Infections were similar in terms of symptoms, risk factors, and proportion of patients hospitalized

Factors determining vaccine uptake in Western Australian adolescents

Aim Adolescence is the final opportunity for a large-scale immunisation programme before adulthood. The Western Australian (WA) school-based vaccination programme provides Year 7 students with free vaccination against hepatitis B virus (HBV); diphtheria, tetanus and pertussis (dTpa); varicella zoster virus (VZV); and human papilloma virus (HPV). We aimed to identify factors determining consent form return and vaccination uptake. Methods Data were collected via a statewide, web-based database in 2009 and 2010. Proportions of students who returned a vaccine consent form, and completed HBV and HPV multi-dose courses and dTpa and VZV vaccination were determined. Factors associated with these outcomes were identified with multivariate analysis using logistic regression, accounting for clustering by school. Results In 2010, 92.8% of WA Year 7 students returned a vaccination consent form and 85.3%, 74.3%, 66.7.0% and 26.4% completed their adolescent vaccination(s) against dTpa, HPV (females only), HBV and VZV, respectively. Consent form return and dTpa vaccination uptake improved between 2009 and 2010. Independent and consistently negative associations were observed between outcome variables (consent form return and vaccine uptake) and male gender, geographically remote schools, government schools and schools in the most socio-economically disadvantaged areas. Both HBV and HPV course completion were higher in Catholic than government schools, and the same in government and independent schools. Conclusion To effectively maximise vaccination coverage, the WA school-based adolescent vaccination programme must specifically target male students and schools in the most disadvantaged and remote areas

Predictors of uptake of influenza vaccination: A survey of pregnant women in Western Australia

Background Pregnant women are at increased risk of complications following influenza infection. Vaccination is the most effective preventive strategy. This survey aimed to determine the levels of uptake of influenza vaccine in pregnant women in Western Australia (WA), the proportion of women offered vaccination as part of antenatal care, and women’s attitudes toward influenza vaccination in pregnancy. Methods Computer assisted telephone interviews were conducted with 416 randomly selected women who were pregnant during the 2012 influenza vaccination season. Results Influenza vaccination coverage was 23%. Predictors of vaccination included believing that vaccination is safe for the infant, having been recommended vaccination by an antenatal care provider, and attending a general practitioner for most antenatal care. The majority (74%) of unvaccinated women reported that they would have the vaccine if their antenatal care provider recommended it

Comparison of the pandemic H1N1 2009 experience in the Southern Hemisphere with pandemic expectations

Objective: To describe the epidemiological characteristics of the 2009 H1N1 pandemic virus (pH1N1) over the 2009 and 2010 influenza seasons in Australia and New Zealand (NZ) and compare them with expectations based on previous pandemics. Methods: Laboratory-confirmed influenza and influenza-like illness (ILI) data were collected from established general practitioner sentinel surveillance schemes in NZ, Victoria and Western Australia (WA) throughout the 2009 and 2010 winter influenza seasons. Respiratory swabs from a sample of ILI patients were tested for influenza type and subtype. ILI rates and laboratory-confirmed influenza data were analysed by age group and over time. Morbidity, mortality and reproductive number data were collated from the published literature. Results: Peak ILI rates and the percentage of influenza-positive swabs from ILI patients from all sentinel surveillance schemes were considerably lower in 2010 than 2009. Compared to the population, cases of ILI were over-represented in the young. While the age distributions in NZ and WA remained consistent, ILI cases were significantly younger in Victoria in 2009 compared to 2010. In Victoria, laboratory-confirmed pH1N1 comprised up to 97% of influenza-positive swabs in 2009 but only 56-87% in 2010. Mortality and hospitalisations were lower in 2010. The effective reproduction number (R) for pH1N1 was estimated to be 1.2-1.5 in NZ and WA, similar to estimated R values for seasonal influenza. Data from the surveillance systems indicated differences in the epidemiology of pH1N1 compared to expectations based on previous pandemics. In particular, there was no evidence of a second pandemic wave associated with increased mortality, and complete influenza strain replacement did not occur. Implications: Pandemic planning needs to accommodate the potential for influenza viruses to produce pandemics of various infectiousness and degrees of severity

Secondary attack rate of pandemic influenza A(H1N1)2009 in Western Australian households, 29 May–7 August 2009

Understanding household transmission of the pandemic influenza A(H1N1)2009 virus, including risk factors for transmission, is important for refining public health strategies to reduce the burden of the disease. During the influenza season of 2009 we investigated transmission of the emerging virus in 595 households in which the index case was the first symptomatic case of influenza A(H1N1)2009. Secondary cases were defined as household contacts with influenza-like illness (ILI) or laboratory-confirmed influenza A(H1N1)2009, occurring at least one day after but within seven days following symptom onset in the index case. ILI developed in 231 of the 1,589 household contacts, a secondary attack rate of 14.5% (95% confidence interval (CI): 12.9–16.4). At least one secondary case occurred in 166 of the 595 households (a household transmission rate of 27.9%; 95% CI: 24.5–31.6). Of these, 127 (76.5%) households reported one secondary case and 39 (23.5%) households reported two or more secondary cases. Secondary attack rates were highest in children younger than five years (p=0.001), and young children were also more efficient transmitters (p=0.01). Individual risk was not associated with household size. Prophylactic antiviral therapy was associated with reduced transmission (p=0.03). The secondary attack rate of ILI in households with a confirmed pandemic influenza A(H1N1)2009 index case was comparable to that described previously for seasonal influenza