The impact of parental postpartum pertussis vaccination on infection in infants: A population-based study of cocooning in Western Australia.

During a pertussis epidemic in 2011-2012 the Western Australian (WA) Department of Health implemented a 'cocooning' programme, offering free pertussis-containing vaccine (dTpa) to new parents. We assessed the impact of vaccinating parents with dTpa on the incidence of pertussis infection in newborns. Births in WA during 2011-2012 were linked to a register of parental pertussis vaccinations and to notified reports of laboratory-proven pertussis in children <6 months of age. Parents who received dTpa during the four weeks after their child's birth were defined as 'vaccinated postpartum.' Cox proportional-hazards methods were used to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for the risk of pertussis infection among infants born to parents vaccinated postpartum vs. unvaccinated parents, adjusted for maternal age, geographic region, timing of birth, and number of siblings. Of 64,364 live-births, 43,480 (68%) infants had at least one vaccinated parent (60% of mothers and 36% of fathers). After excluding records where parent(s) were either vaccinated prior to the birth, vaccinated >28 days after the birth, the vaccination date was uncertain, or the child died at birth (n=42), the final cohort contained 53,149 children, 118 of whom developed pertussis. There was no difference in the incidence of pertussis among infants whose parents were both vaccinated postpartum compared to those with unvaccinated parents (1.9 vs 2.2 infections per 1000 infants; adjusted HR 0.91; 95%CI 0.55-1.53). Similarly, when assessed independently, maternal postpartum vaccination was not protective (adjusted HR 1.19; 95%CI 0.82-1.72). Supplemental sensitivity analyses which varied the time period for parental vaccination and accounted for under-reporting of vaccination status did not significantly alter these findings. In our setting, vaccinating parents with dTpa during the four weeks following delivery did not reduce pertussis diagnoses in infants. WA now provides dTpa vaccine to pregnant women during the third trimester.

Intussusception is associated with the detection of adenovirus C, enterovirus B and rotavirus in a rotavirus vaccinated population.

BACKGROUND: Intussusception, a condition where one segment of intestine invaginates into another, occurs predominantly in infants and young children. A number of potential causes have been identified including infectious agents and rotavirus vaccination. Following the introduction of rotavirus vaccination of infants in Western Australia, a laboratory surveillance programme testing notified intussusception cases for infectious agents was commenced. This led to a PCR-based study of the association between gastrointestinal viruses and intussusception. OBJECTIVES: Conduct viral testing on stool samples from intussusception patients to determine viruses that may have an association with intussusception. STUDY DESIGN: A retrospective case-control study was conducted using stool samples collected from children with intussusception (n=74) and matched controls (n=289) between 2008 and 2011. Samples were tested for rotavirus, norovirus, adenovirus, enterovirus, rhinovirus, astrovirus, parechovirus and bocavirus. Adenovirus, enterovirus and rhinovirus species were determined by DNA sequencing. RESULTS: Human adenovirus C was detected in significantly more cases than controls with 31/74 (41.9%) cases testing positive compared to 39/289 (13.49%) controls (OR=4.38, p<0.001). A significant difference was seen in Enterovirus B detections with 11/74 (14.9%) cases testing positive compared to 21/289 (7.3%) controls (OR=2.24, p=0.04). Rotavirus was detected in 7/74 (9.46%) cases and 11/289 (3.81%) controls, which was also a significant difference (OR=2.88, p=0.045). CONCLUSIONS: Our results show that intussusception is associated with non-enteric adenovirus infections, and Enterovirus B infections. While a statistical association was seen with rotavirus and intussusception, we were not able to determine if this was related to vaccine strain or wild type rotavirus.

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. DISCUSSION: General practitioners lead the way in antenatal influenza vaccination in WA. Vaccination coverage can be improved if recommending and offering influenza vaccination becomes a routine part of antenatal care.

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.

Clinical Predictors of Influenza in Young Children: The Limitations of "Influenza-Like Illness".

BACKGROUND: Influenza-like illness (ILI) definitions have been infrequently studied in young children. Despite this, clinical definitions of ILI play an important role in influenza surveillance. This study aims to identify clinical predictors of influenza infection in children ≤5 years old from which age-specific ILI definitions are then constructed. METHODS: Children aged 6-59 months with a history of fever and acute respiratory symptoms were recruited in the Western Australia Influenza Vaccine Effectiveness (WAIVE) Study. Clinical data and per-nasal specimens were obtained from all children. Logistic regression identified significant predictors of influenza infection. Different ILI definitions were compared for diagnostic accuracy. RESULTS: Children were recruited from 2 winter influenza seasons (2008-2009; n = 944). Of 919 eligible children, 179 (19.5%) had laboratory-confirmed influenza infection. Predictors of infection included increasing age, lack of influenza vaccination, lower birth weight, fever, cough, and absence of wheeze. An ILI definition comprising fever ≥38°C, cough, and no wheeze had 58% sensitivity (95% confidence interval [CI], 50-66), 60% specificity (95% CI, 56-64), 26% positive predictive value (95% CI, 21-31), and 86% negative predictive value (95% CI, 82-89). The addition of other symptoms or higher fever thresholds to ILI definition had little impact. The Centers for Disease Control and Prevention definition of ILI (presence of fever [≥37.8°C] and cough and/or sore throat) was sensitive (92%; 95% CI, 86-95), yet lacked specificity (10%; 95% CI, 8-13) in this population. CONCLUSIONS: Influenza-like illness is a poor predictor of laboratory-confirmed influenza infection in young children but can be improved using age-specific data. Incorporating age-specific ILI definitions and/or diagnostic testing into influenza surveillance systems will improve the accuracy of epidemiological data.

Chronic disease and hospitalisation for pandemic (H1N1) 2009 influenza in Indigenous and non-Indigenous Western Australians.

Indigenous and non-indigenous Western Australians with pandemic (H1N1) 2009 influenza (pH1N1) infection were compared for risk factors, influenza vaccination history, symptoms, use of antiviral medications, and hospitalisation. Data were collected systematically on 856 notified cases with laboratory confirmed pH1N1 infection during the first 10 weeks of pH1N1 virus transmission in Western Australia in 2009. Indigenous people with pH1N1 were approximately 3 times more likely to be hospitalised and were more likely to have a range of underlying medical conditions and be smokers, compared with non-Indigenous cases. Age (P < 0.001) and the presence of two or more co-morbidities (P < 0.001) were independent predictors of hospitalisation, while Indigenous status was not, indicating that higher pH1N1 hospitalisation rates in Indigenous Australians during the 2009 winter season were attributable to the higher prevalence of underlying chronic disease. These results underscore the need to ensure that influenza vaccination is delivered as widely as possible among those with chronic health conditions.

Reactogenicity of two 2010 trivalent inactivated influenza vaccine formulations in adults.

OBJECTIVE: To assess the reactogenicity of two 2010 trivalent inactivated influenza vaccine (TIV) formulations among adults, including the formulation associated with febrile convulsions among children in Australia. DESIGN, SETTING AND PARTICIPANTS: We retrospectively interviewed persons aged ≥18 years who received TIV between 11 March and 24 April 2010 at a large general practice in Perth. All 160 persons who received Influvac® (Solvay) and a random sample of 190 of 451 persons who received Fluvax® (CSL Biotherapies) were included in the assessment; 127 (79%) recipients of Influvac® and 156 (82%) of the Fluvax® recipients completed the interview. MAIN OUTCOME MEASURES: Patient demographics, the presence of underlying medical conditions, prior influenza vaccination history, self-reported onset of local and/or systemic symptoms within 72 h following receipt of 2010 TIV, and use of anti-fever/pain medication following TIV vaccination were examined. RESULTS: The mean age of the vaccinees was 54 years for both the Fluvax® and Influvac® brand cohorts and there was no significant difference between the cohorts with regard to gender or the presence of underlying medical conditions. In bivariate analyses, reported swelling (18% vs 7%, p=0.009), muscle pain (12% vs 3%, p=0.014) and use of anti-fever/pain medication after TIV vaccination (12% vs 2%, p=0.008) were each significantly more common for patients who received Fluvax® compared to those who received Influvac®. In multivariate analyses simultaneously controlling for age, gender, receipt of seasonal influenza vaccine prior to 2010 and receipt of 2009 H1N1 pandemic vaccine, vaccination with Fluvax® TIV was a significant independent predictor of muscle pain and/or swelling (OR=3.3, 95% CI 1.5-7.4 p=0.004). No significant differences in the proportion of patients reporting systemic reactions were observed. CONCLUSIONS: In this setting, 2010 Fluvax® was associated with a greater likelihood of local reactions among adults, compared to 2010 Influvac® TIV.

Marketing paediatric influenza vaccination: results of a major metropolitan trial.

OBJECTIVES: After a cluster of rapidly fulminant influenza related toddler deaths in a Western Australian metropolis, children aged six to 59 months were offered influenza vaccination in subsequent winters. Some parental resistance was expected and previous poor uptake of paediatric influenza vaccination overseas was noted. A marketing campaign addressing barriers to immunization was developed to maximise uptake. DESIGN: Advertising occurred in major statewide newspapers, via public poster displays and static 'eye-lite' displays, via press releases, via a series of rolling radio advertisements, via direct marketing to child care centres, and via a linked series of web-sites. Parents were subsequently surveyed to assess reasons for vaccination. MAIN OUTCOME RESULTS: The campaign produced influenza vaccination coverage above that previously described elsewhere and led to a proportionate reduction in influenza notifications in this age group compared to previous seasons. CONCLUSIONS: Influenza in children comes with significant morbidity and some mortality. Paediatric influenza vaccination is safe, well tolerated and effective if two doses are given. A targeted media campaign can increase vaccine uptake if it reinforces the seriousness of influenza and addresses community 'myths' about influenza and influenza vaccine. The lessons learned enabling enhancements of similar programs elsewhere.

Vaccine Effectiveness Against Laboratory-confirmed Influenza in Healthy Young Children: A Case-Control Study.

BACKGROUND: the Western Australian Influenza Vaccine Effectiveness study commenced in 2008 to evaluate a new program to provide free influenza vaccine to all children aged 6 to 59 months. We aimed to assess the protective effect of inactivated influenza vaccination in these children. METHODS: We conducted a prospective case-control study in general practices and a hospital emergency department, testing all eligible patients for influenza and a range of other common respiratory viruses. Influenza vaccine effectiveness (VE) against laboratory-confirmed influenza was estimated with cases defined as children with an influenza-like illness who tested positive and controls as those with an influenza-like illness who tested negative for influenza virus. We calculated VE using the adjusted odds ratio from multivariate logistic regression. As a surrogate marker for adequate specimen collection, we explored the difference in VE point estimates defining controls as children in whom another respiratory virus was detected. RESULTS: a total of 75 children were enrolled from general practices and 214 through the emergency department, with 12 (27%) and 36 (17%), respectively, having laboratory-confirmed influenza. Using all the influenza-negative controls, the adjusted VE was 58% (95% confidence interval, 9-81). When controls were limited to those with another virus present, the adjusted VE was 68% (95% confidence interval, 26-86). CONCLUSIONS: VE estimates were higher when controls included only those children with another respiratory virus detected. Testing for other common respiratory viruses enables the control group to be restricted to those for whom an adequate sample is likely.

Comparison of pandemic (H1N1) 2009 and seasonal influenza, Western Australia, 2009.

We compared confirmed pandemic (H1N1) 2009 influenza and seasonal influenza diagnosed in Western Australia during the 2009 influenza season. From 3,178 eligible reports, 984 pandemic and 356 seasonal influenza patients were selected; 871 (88.5%) and 288 (80.9%) were interviewed, respectively. Patients in both groups reported a median of 6 of 11 symptoms; the difference between groups in the proportion reporting any given symptom was < or =10%. Fewer than half the patients in both groups had > or =1 underlying condition, and only diabetes was associated with pandemic (H1N1) 2009 influenza (odds ratio [OR] 1.9, 95% confidence interval [CI] 1.1-3.5). A total of 129 (14.8%) persons with pandemic (H1N1) 2009 and 36 (12.5%) persons with seasonal influenza were hospitalized (p = 0.22). After controlling for age, we found that patient hospitalization was associated with pandemic (H1N1) 2009 influenza (OR 1.5; 95% CI 1.1-2.1). Contemporaneous pandemic and seasonal influenza infections were substantially similar in terms of patients' symptoms, risk factors, and proportion hospitalized.

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.

Lessons from the first year of the WAIVE study investigating the protective effect of influenza vaccine against laboratory-confirmed influenza in hospitalised children aged 6-59 months.

BACKGROUND: Influenza is major cause of paediatric hospitalisation. Influenza vaccine was offered to all children aged 6-59 months resident in Western Australia in 2008, and we wished to evaluate the effectiveness of this immunisation programme. OBJECTIVES: To assess the practicalities of a nested matched case-control design to estimate the protective effect of inactivated influenza vaccination in hospitalised children aged 6-59 months. METHODS: Cases were hospitalised children with laboratory-confirmed influenza, while matched controls were recruited from children admitted for an acute non-respiratory illness. We estimated influenza vaccine effectiveness (VE) against influenza as 1--the adjusted odds ratio from multivariate logistic regression. RESULTS: The 2008 influenza season was characterised by a late peak and a predominance of influenza virus B. We recruited 26 hospitalised patients with laboratory-confirmed influenza and 50 matched controls. The proportion of cases who were fully vaccinated was 7% versus 30% of controls giving an adjusted VE of 83% (95% CI--54 to 98). CONCLUSIONS: Recruiting sufficient controls was problematic and in the future, we will select controls hospitalised for an influenza-like-illness but influenza negative by laboratory PCR testing. The VE estimate was high but non-significant, reflecting the low number of cases.

Household responses to pandemic (H1N1) 2009-related 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 >or=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 >or=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.