What do epidemiologists expect with containment, mitigation, business-as-usual strategies for swine-origin human influenza A?

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1 What do epidemiologists expect with containment, mitigation, business-as-usual strategies for swine-origin human influenza A? Dr Thomas TSANG Controller, Centre for Health Protection, Department of Health 18 July 2009

2 Containment ( ) Intended to stop - or at least slow down - a human influenza pandemic before it has the opportunity to spread No / small number of cases, limited local transmission E.g., border screening, case isolation, contact tracing, quarantine, chemoprophylaxis

3 Mitigation ( ) Relief disease burden and impact by human pandemic influenza When containment no longer feasible significant number of cases or local transmission E.g., Personal protection measures, self-care, social distancing, medical resource mobilization, anti-viral treatment

4 Evidence for containment Containing pandemic influenza with antiviral agents (Am J Epidemiol Apr 1;159(7):623-33) Model of an influenza pandemic / bioterrorist attack for an agent similar to the pandemic of Simulated influenza case and death rates and effectiveness of interventions based on 200 simulations VEIII = overall effectiveness; EPP = epidemic prevention potential; CI = confidence interval.

5 Evidence for containment Modeling the worldwide spread of pandemic influenza: baseline case and containment interventions (PLoS Med Jan;4(1):e13) For R 0 up to 1.9: Large-scale therapeutic usage of antivirals in all hit countries could mitigate pandemic effect during first year For 1.9 < R 0 < 2.3: Even treatment of 20% of population leaves 30-50% of the population infected In the case of limited antiviral supplies and pandemics with R 0 as high as 1.9, the more cooperative the strategy, the more effective are the containment results in all regions of the world

7 Evidence for containment Australian experience during 1918 pandemic flu Oct 1918, Australia began to quarantine arriving ships upon which a case of influenza had occurred during voyage Oct May 1919, 79 infected vessels containing 2,795 patients, 48,072 passengers, and 10,456 crew arrived at Australian ports First cases in Australia reported in Jan 1919, suggesting that these measures delayed entry of the disease for 3 months

8 Pandemic travel time from literature Baseline Scenario with No Containment Intervention: Attack Rates and Peak Time in Different Geographical Areas Source: PLoS Med Jan;4(1):e13

9 Containment Does it work in practice? 26/4/09 Source:

10 Containment Does it work in practice?

11 Containment Does it work in practice?

12 Containment Does it work in practice?

13 Containment Does it work in practice?

14 HK containment objective DELAY, not prevent, local transmission for as long as possible Buy time for understanding virus properties development of diagnostic tests medical services preparation school holiday vaccine

16 HK containment strategies

17 HK containment strategies

18 Containment phase statistics From 1 May - 17 June (containment phase): 197 cases isolated Traced 71 planes & 1 train Quarantined ~280 contacts in camps Put ~1,300 persons on directly observed chemoprophylaxis (DOC)

19 The turning point Outbreak of HSI in St. Paul s Convent School (Secondary Section) on 11 June 2009 First cluster of indigenous HSI cases in Hong Kong Gradual transition from containment to mitigation

20 Mitigation objectives Slow down epidemic progress Prevent large explosive outbreaks Focus on individuals at risk of serious illness Avoid overloading medical system Reduce impact of epidemic on society

21 Evidence for social distancing Simulation suggests that rapid activation of social distancing can arrest epidemic development due to a novel strain of influenza (BMC Public Health Apr 29;9:117) For an epidemic with R 0 =1.5, a combination of social distancing measures could reduce the final attack rate from 33% to below 10% if introduced within 6 weeks from the introduction of the first case Social distancing measures in the study referred to school closure, increased isolation of symptomatic individuals in household, workplace nonattendance, and reduction of contact in the wider community)

23 Effect of social distancing on respiratory viruses isolation Respiratory Infections during SARS Outbreak, Hong Kong, 2003 (Emerg Infect Dis Nov;11(11): ) Effect of community hygienic measures during SARS outbreak studied by comparing proportion of +ve specimens of various respiratory viruses in 2003 with those from 1998 to 2002 Community hygienic measures significantly reduced incidence of respiratory viral infections

24 Evidence for school closure Israeli studies (effect of nationwide elementary school teachers strike in 2000): Changes in weekly ratio of ILI diagnoses to nonrespiratory diagnoses statistically significant (P=0 0074) for school children for the strike year compared to other years (A. D. HEYMANN, et al. Epidemiology and Infection, 07 Apr 2009) Significant decreases in diagnoses of respiratory infections (42%), visits to physicians (28%) and emergency departments (28%), and medication purchases (35%) among children (Pediatric Infectious Disease Journal 2004; 23: )

25 Evidence for school closure French study (Nature 2008; 452: ) Analysis of surveillance data and holiday timing Holidays lead to a 20-29% reduction in rate at which influenza is transmitted to children; prevent 16-18% of seasonal influenza cases (18-21% in children). By extrapolation: prolonged school closure might reduce cumulative number of cases by 13-17% (18-23% in children) and peak attack rates by up to 39-45% (47-52% in children)

26 Evidence for school closure Mathematical modeling (Eurosurveillance, Vol. 14, Issue 24) Assess impact of intervention strategies on spread of HSI in European setting When initiating 100% school closure in a community of 2,000 people at a threshold of 1% cumulative attack rate, total number of symptomatic cases is predicted to decrease by 89.3%

27 Effect of school closure in HK (2008 Easter) Sentinel ILI consultation rates (GOPCs/GPs) Influenza virus isolation at Public Health Laboratory Centre : school closure period

28 Effect of school closure on respiratory viruses isolation (2008) Effects of School Closures, 2008 Winter Influenza Season, Hong Kong (Emerg Infect Dis Oct;14(10):1660-2) In winter 2008, kindergartens and primary schools in Hong Kong were closed for 2 weeks after media coverage indicated that 3 children had died, apparently from influenza Reviewed prospective surveillance data on influenza and ILI activity Authors noted a decline in laboratory isolations of influenza viruses that preceded the intervention and the lack of association between school closures and the effective reproductive number R t

29 Mitigation phase measures Class suspension / early summer breaks for All primary schools, kindergartens, child-care centres and special schools Secondary schools with confirmed case(s) Personal hygiene campaign Provide relevant information and guidelines to different sectors and stakeholders in the community, and mobilize them to initiate response plans

30 Mitigation phase measures 8 Designated Flu Clinics for managing patients with fever and influenza-like illnesses (ILI) Priority to pregnant women, aged <2 years, high risk groups Tamiflu only given to ILI patients with chronic diseases or immuno-compromised states New hospital admission criteria Based on clinical condition HSI patients with mild symptoms would not be admitted

31 Evolution of HSI epidemic in HK

32 % of HSI among DFC attendees

33 Flu virus isolates by week Influenza virus detections (Laboratory Surveillance),

34 From now on, business as usual? Virus mutation Change in severity, antiviral resistance Winter peak and surges HSI vaccination challenges

35 What else from here? Surveillance and monitoring Sustained publicity campaign Antiviral stockpile replenishment Vaccination preparations

Ralph KY Lee Honorary Secretary HKIOEH

HKIOEH Round Table: Updates on Human Swine Influenza Facts and Strategies on Disease Control & Prevention in Occupational Hygiene Perspectives 9 July 2009 Ralph KY Lee Honorary Secretary HKIOEH 1 Influenza