We built a SEIR (susceptible, exposed, infected, recovered) model of smallpox transmission for New York, New York, USA, and Sydney, New South Wales, Australia, that accounted for age-specific population immunosuppression and residual vaccine immunity and conducted sensitivity analyses to estimate the effect these parameters might have on smallpox reemergence. At least 19% of New York’s and 17% of Sydney’s population are immunosuppressed. The highest smallpox infection rates were in persons 0–19 years of age, but the highest death rates were in those >45 years of age. Because of the low level of residual vaccine immunity, immunosuppression was more influential than vaccination on death and infection rates in our model. Despite widespread smallpox vaccination until 1980 in New York, smallpox outbreak severity appeared worse in New York than in Sydney. Immunosuppression is highly prevalent and should be considered in future smallpox outbreak models because excluding this factor probably underestimates death and infection rates.

Objectives: Infection control policies and guidelines recommend using facemasks and respirators to protect healthcare workers (HCWs) from respiratory infections. Common types of respirators used in healthcare settings are filtering facepiece respirators (FFRs) and powered air-purifying respirators (PAPRs). Aims of this study were to examine the current attitudes and practices of HCWs regarding the selection and use of respiratory protection and determine the acceptability of a novel PAPR. Methods: In-depth interviews were undertaken with 20 HCWs from a large tertiary hospital in Sydney, Australia. Participants were fit tested with a lightweight tight-fitting half-facepiece PAPR (CleanSpace2™ Power Unit, PAF-0034, by CleanSpace Technology®) using the TSI™ Portacount quantitative fit test method. Results: Interview results showed that HCWs had a limited role in the selection and use of facemasks and respirators and had been using the devices provided by the hospital. The majority of subjects had no knowledge of hospital policy for the use of facemasks and respirators, had not been trained on the use of respirators, and had not been fit tested previously. Compliance with the use of facemasks and respirators was perceived as being low and facemasks and respirators were typically used only for short periods of time. All 20 participants were successfully fit tested to the CleanSpace2™ PAPR (overall geometric mean fit factor-6768). According to the exit surveys, CleanSpace2™ PAPRs were easy to don (14/20) and doff (15/20) and comfortable to wear (14/20). Most participants believed that PAPRs provide higher protection, comfort and reusability over N95 FFR and can be used during pandemics and other high-risk situations.

Introduction Smallpox has been eradicated but advances in synthetic biology have increased the risk of its re-emergence. Residual immunity in individuals who were previously vaccinated may mitigate the impact of an outbreak, but there is a high degree of uncertainty about the duration and degree of residual immunity. Both cell-mediated and humoral immunity are thought to be important but the exact mechanisms of protection are unclear. Guidelines usually suggest vaccine-induced immunity wanes to zero after 3–10 years post vaccination, whereas other estimates show long term immunity over decades. Materials and Methods A systematic review of the literature was conducted to quantify the duration and extent of residual immunity to smallpox after vaccination. Results Twenty-nine papers related to quantifying residual immunity to smallpox after vaccination were identified: neutralizing antibody levels were used as immune correlates of protection in 11/16 retrospective cross-sectional studies, 2/3 epidemiological studies, 6/7 prospective vaccine trials and 0/3 modeling studies. Duration of protection of >20 years was consistently shown in the 16 retrospective cross-sectional studies, while the lowest estimated duration of protection was 11.7 years among the modeling studies. Childhood vaccination conferred longer duration of protection than vaccination in adulthood, and multiple vaccinations did not appear to improve immunity. Conclusions Most studies suggest a longer duration of residual immunity (at least 20 years) than assumed in smallpox guidelines. Estimates from modeling studies were less but still greater than the 3–10 years suggested by the WHO Committee on International Quarantine or US CDC guidelines. These recommendations were probably based on observations and studies conducted while smallpox was endemic. The cut-off values for pre-existing antibody levels of >1:20 and >1:32 reported during the period of endemic smallpox circulation may not be relevant to the contemporary population, but have been used as a threshold for identifying people with residual immunity in post-eradication era studies. Of the total antibodies produced in response to smallpox vaccination, neutralizing antibodies have shown to contribute significantly to immunological memory. Although the mechanism of immunological memory and boosting is unclear, revaccination is likely to result in a more robust response. There is a need to improve the evidence base for estimates on residual immunity to better inform planning and preparedness for re-emergent smallpox.

Planning for a re-emergent epidemic of smallpox requires surge capacity of space, resources and personnel within health systems. There are many uncertainties in such a scenario, including likelihood and size of an attack, speed of response and health system capacity. We used a model for smallpox transmission to determine requirements for hospital beds, contact tracing and health workers (HCWs) in Sydney, Australia, during a modelled epidemic of smallpox. Sensitivity analysis was done on attack size, speed of response and proportion of case isolation and contact tracing. We estimated 100638 clinical HCWs and 14595 public hospital beds in Sydney. Rapid response, case isolation and contact tracing are influential on epidemic size, with case isolation more influential than contact tracing. With 95% of cases isolated, outbreak control can be achieved within 100 days even with only 50% of contacts traced. However, if case isolation and contact tracing both fall to 50%, epidemic control is lost. With a smaller initial attack and a response commencing 20 days after the attack, health system impacts are modest. The requirement for hospital beds will vary from up to 4% to 100% of all available beds in best and worst case scenarios. If the response is delayed, or if the attack infects 10000 people, all available beds will be exceeded within 40 days, with corresponding surge requirements for clinical health care workers (HCWs). We estimated there are 330 public health workers in Sydney with up to 940,350 contacts to be traced. At least 3 million respirators will be needed for the first 100 days. To ensure adequate health system capacity, rapid response, high rates of case isolation, excellent contact tracing and vaccination, and protection of HCWs should be a priority. Surge capacity must be planned. Failures in any of these could cause health system failure, with inadequate beds, quarantine spaces, personnel, PPE and inability to manage other acute health conditions.

ObjectiveTo understand the global outbreak surveillance needs of stakeholders involved in epidemic response in selected countries and areas in the Asia–Pacific region to inform development of an epidemic observatory, Epi-watch.MethodsWe designed an online, semi-structured stakeholder questionnaire to collect information on global outbreak surveillance sources and limitations from participants who use epidemic intelligence and outbreak alert services in their work in government and nongovernment organizations in the Asia–Pacific region.ResultsAll respondents agreed that it was important to remain up to date with global outbreaks. The main reason cited for following global outbreak news was as an early warning for serious epidemics. Mainstream media and specialist Internet sources such as the World Health Organization (n = 54/91; 59%), the Program for Monitoring Emerging Diseases (ProMED)-mail (n = 45/91; 49%) and the United States Centers for Disease Control and Prevention (n = 31/91; 34%) were the most common sources for global outbreak news; rapid intelligence services such as HealthMap were less common (n = 9/91; 10%). Only 51% (n = 46/91) of respondents thought that their sources of outbreak news were timely and sufficient for their needs.ConclusionFor those who work in epidemic response, epidemic intelligence is important and widely used. Stakeholders are less aware of and less frequently use rapid sources such as HealthMap and rely more on validated but less timely traditional sources of disease surveillance. Users identified a need for more timely and reliable epidemic intelligence.