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Zhang Q, Wang D. Assessing the Role of Voluntary Self-Isolation in the Control of Pandemic Influenza Using a Household Epidemic Model. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2015; 12:9750-67. [PMID: 26295248 PMCID: PMC4555310 DOI: 10.3390/ijerph120809750] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/15/2015] [Revised: 08/06/2015] [Accepted: 08/12/2015] [Indexed: 11/16/2022]
Abstract
In the absence of effective vaccines, antiviral drugs and personal protective measures, such as voluntary self-isolation, have been a part of preparedness plans for the next influenza pandemic. We used a household model to assess the effect of voluntary self-isolation on outbreak control when antiviral drugs are not provided sufficiently early. We found that the early initiation of voluntary self-isolation can overcome the negative effects caused by a delay in antiviral drug distribution when enough symptomatic individuals comply with home confinement at symptom onset. For example, for the baseline household reproduction number RH0 = 2:5, if delays of one or two days occur between clinical symptom development and the start of antiviral prophylaxis, then compliance rates of q ≥ 0:41 and q ≥ 0:6, respectively, are required to achieve the same level of effectiveness as starting antiviral prophylaxis at symptom onset. When the time to beginning voluntary self-isolation after symptom onset increases from zero to two days, this strategy has a limited effect on reducing the transmission of influenza; therefore, this strategy should be implemented as soon as possible. In addition, the effect of voluntary self-isolation decreases substantially with the proportion of asymptomatic infections increasing.
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Affiliation(s)
- Qingxia Zhang
- School of Mathematical Sciences, University of Electronic Science and Technology of China, No. 2006, Xiyuan Avenue, West Hi-Tech Zone, Chengdu 611731, China.
- School of Sciences, Southwest Petroleum University, No.8, Xindu Avenue, Xindu District, Chengdu 610500, China.
| | - Dingcheng Wang
- School of Mathematical Sciences, University of Electronic Science and Technology of China, No. 2006, Xiyuan Avenue, West Hi-Tech Zone, Chengdu 611731, China.
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Greer AL, Schanzer D. Using a Dynamic Model to Consider Optimal Antiviral Stockpile Size in the Face of Pandemic Influenza Uncertainty. PLoS One 2013; 8:e67253. [PMID: 23805303 PMCID: PMC3689716 DOI: 10.1371/journal.pone.0067253] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Accepted: 05/14/2013] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The Canadian National Antiviral Stockpile (NAS) contains treatment for 17.5% of Canadians. This assumes no concurrent intervention strategies and no wastage due to non-influenza respiratory infections. A dynamic model can provide a mechanism to consider complex scenarios to support decisions regarding the optimal NAS size under uncertainty. METHODS We developed a dynamic model for pandemic influenza in Canada that is structured by age and risk to calculate the demand for antivirals to treat persons with pandemic influenza under a wide-range of scenarios that incorporated transmission dynamics, disease severity, and intervention strategies. The anticipated per capita number of acute respiratory infections due to viruses other than influenza was estimated for the full pandemic period from surveys based on criteria to identify potential respiratory infections. RESULTS Our results demonstrate that up to two thirds of the population could develop respiratory symptoms as a result of infection with a pandemic strain. In the case of perfect antiviral allocation, up to 39.8% of the population could request antiviral treatment. As transmission dynamics, severity and timing of the emergence of a novel influenza strain are unknown, the sensitivity analysis produced considerable variation in potential demand (median: 11%, IQR: 2-21%). If the next pandemic strain emerges in late spring or summer and a vaccine is available before the anticipated fall wave, the median prediction was reduced to 6% and IQR to 0.7-14%. Under the strategy of offering empirical treatment to all patients with influenza like symptoms who present for care, demand could increase to between 65 and 144%. CONCLUSIONS The demand for antivirals during a pandemic is uncertain. Unless an accurate, timely and cost-effective test is available to identify influenza cases, demand for antivirals from persons infected with other respiratory viruses will be substantial and have a significant impact on the NAS.
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Affiliation(s)
- Amy L. Greer
- Modelling and Projection Section, Professional Guidelines and Public Health Practice Division, Centre for Communicable Diseases and Infection Control, Public Health Agency of Canada, Ottawa, Ontario, Canada
- Division of Epidemiology, Dalla Lana School of Public Health, University of Toronto, Toronto, Ontario, Canada
| | - Dena Schanzer
- Modelling and Projection Section, Professional Guidelines and Public Health Practice Division, Centre for Communicable Diseases and Infection Control, Public Health Agency of Canada, Ottawa, Ontario, Canada
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McCaw JM, Howard PF, Richmond PC, Nissen M, Sloots T, Lambert SB, Lai M, Greenberg M, Nolan T, McVernon J. Household transmission of respiratory viruses - assessment of viral, individual and household characteristics in a population study of healthy Australian adults. BMC Infect Dis 2012; 12:345. [PMID: 23231698 PMCID: PMC3538067 DOI: 10.1186/1471-2334-12-345] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2012] [Accepted: 12/06/2012] [Indexed: 02/04/2023] Open
Abstract
Background Household transmission of influenza-like illness (ILI) may vary with viral and demographic characteristics. We examined the effect of these factors in a population-based sample of adults with ILI. Methods We conducted a prospective cohort study in community-dwelling Australian adults nested within an influenza vaccine effectiveness trial. On presentation with ILI, participants were swabbed for a range of respiratory viruses and asked to return a questionnaire collecting details of household members with or without similar symptoms. We used logistic and Poisson regression to assess the key characteristics of household transmission. Results 258 participants from multi-occupancy households experienced 279 ILI episodes and returned a questionnaire. Of these, 183 were the primary case in the household allowing assessment of factors associated with transmission. Transmission was significantly associated in univariate analyses with female sex (27% vs. 13%, risk ratio (RR) = 2.13 (1.08, 4.21)) and the presence of a child in the house (33% vs. 17%, RR = 1.90 (1.11, 3.26)). The secondary household attack proportion (SHAP) was 0.14, higher if influenza was isolated (RR = 2.1 (1.0, 4.5)). Vaccinated participants who nonetheless became infected with influenza had a higher SHAP (Incidence RR = 5.24 (2.17, 12.6)). Conclusions The increased SHAP in households of vaccinated participants who nonetheless had confirmed influenza infection supports the hypothesis that in years of vaccine mismatch, not only is influenza vaccine less protective for the vaccine recipient, but that the population’s immunity is also lower.
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Affiliation(s)
- James M McCaw
- Murdoch Children's Research Institute & Melbourne School of Population Health, The University of Melbourne, Parkville, Victoria, 3010, Australia.
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Pebody RG, Harris R, Kafatos G, Chamberland M, Campbell C, Nguyen-Van-Tam JS, McLean E, Andrews N, White PJ, Wynne-Evans E, Green J, Ellis J, Wreghitt T, Bracebridge S, Ihekweazu C, Oliver I, Smith G, Hawkins C, Salmon R, Smyth B, McMenamin J, Zambon M, Phin N, Watson JM. Use of antiviral drugs to reduce household transmission of pandemic (H1N1) 2009, United Kingdom. Emerg Infect Dis 2011. [PMID: 21749759 PMCID: PMC3358196 DOI: 10.3201/eid1706.101161] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
TOC Summary: Early treatment of primary case-patients and prophylaxis of household contacts provides effective protection. The United Kingdom implemented a containment strategy for pandemic (H1N1) 2009 through administering antiviral agents (AVs) to patients and their close contacts. This observational household cohort study describes the effect of AVs on household transmission. We followed 285 confirmed primary cases in 259 households with 761 contacts. At 2 weeks, the confirmed secondary attack rate (SAR) was 8.1% (62/761) and significantly higher in persons <16 years of age than in those >50 years of age (18.9% vs. 1.2%, p<0.001). Early (<48 hours) treatment of primary case-patients reduced SAR (4.5% vs. 10.6%, p = 0.003). The SAR in child contacts was 33.3% (10/30) when the primary contact was a woman and 2.9% (1/34) when the primary contact was a man (p = 0.010). Of 53 confirmed secondary case-patients, 45 had not received AV prophylaxis. The effectiveness of AV prophylaxis in preventing infection was 92%.
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Abstract
Modelling is valuable in the planning and evaluation of interventions, especially when a controlled trial is ethically or logistically impossible. Models are often used to calculate the expected course of events in the absence of more formal assessments. They are also used to derive estimates of rare or future events from recorded intermediate points. When developing models, decisions are needed about the appropriate level of complexity to be represented and about model structure and assumptions. The degree of rigor in model development and assessment can vary greatly, and there is a danger that existing beliefs inappropriately influence judgments about model assumptions and results.
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Affiliation(s)
- Geoffrey P Garnett
- Department of Infectious Disease Epidemiology, Imperial College London, London, UK
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Pebody RG, Harris R, Kafatos G, Chamberland M, Campbell C, Nguyen-Van-Tam JS, McLean E, Andrews N, White PJ, Wynne-Evans E, Green J, Ellis J, Wreghitt T, Bracebridge S, Ihekweazu C, Oliver I, Smith G, Hawkins C, Salmon R, Smyth B, McMenamin J, Zambon M, Phin N, Watson JM. Use of Antiviral Drugs to Reduce Household Transmission of Pandemic (H1N1) 2009, United Kingdom1. Emerg Infect Dis 2011; 17:990-9. [DOI: 10.3201/eid/1706.101161] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Becker NG, Wang D. Can antiviral drugs contain pandemic influenza transmission? PLoS One 2011; 6:e17764. [PMID: 21464934 PMCID: PMC3065466 DOI: 10.1371/journal.pone.0017764] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Accepted: 02/09/2011] [Indexed: 12/01/2022] Open
Abstract
Antiviral drugs dispensed during the 2009 influenza pandemic generally failed to
contain transmission. This poses the question of whether preparedness for a
future pandemic should include plans to use antiviral drugs to mitigate
transmission. Simulations using a standard transmission model that allows for infected arrivals
and delayed vaccination show that attempts to contain transmission require
relatively few antiviral doses. In contrast, persistent use of antiviral drugs
when the reproduction number remains above 1 use very many doses and are
unlikely to reduce the eventual attack rate appreciably unless the stockpile is
very large. A second model, in which the community has a household structure,
shows that the effectiveness of a strategy of dispensing antiviral drugs to
infected households decreases rapidly with time delays in dispensing the
antivirals. Using characteristics of past pandemics it is estimated that at
least 80% of primary household cases must present upon show of symptoms
to have a chance of containing transmission by dispensing antiviral drugs to
households. To determine data needs, household outbreaks were simulated with
50% receiving antiviral drugs early and 50% receiving antiviral
drugs late. A test to compare the size of household outbreaks indicates that at
least 100–200 household outbreaks need to be monitored to find evidence
that antiviral drugs can mitigate transmission of the newly emerged virus. Use of antiviral drugs in an early attempt to contain transmission should be part
of preparedness plans for a future influenza pandemic. Data on the incidence of
the first 350 cases and the eventual attack rates of the first 200 hundred
household outbreaks should be used to estimate the initial reproduction number
R and the effectiveness of antiviral drugs to mitigate
transmission. Use of antiviral drugs to mitigate general transmission should
cease if these estimates indicate that containment of transmission is
unlikely.
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Affiliation(s)
- Niels G Becker
- National Centre for Epidemiology and Population Health, The Australian National University, Canberra, Australian Capital Territory, Australia.
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van Boven M, Donker T, van der Lubben M, van Gageldonk-Lafeber RB, te Beest DE, Koopmans M, Meijer A, Timen A, Swaan C, Dalhuijsen A, Hahné S, van den Hoek A, Teunis P, van der Sande MAB, Wallinga J. Transmission of novel influenza A(H1N1) in households with post-exposure antiviral prophylaxis. PLoS One 2010; 5:e11442. [PMID: 20628642 PMCID: PMC2898802 DOI: 10.1371/journal.pone.0011442] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2009] [Accepted: 05/26/2010] [Indexed: 11/19/2022] Open
Abstract
Background Despite impressive advances in our understanding of the biology of novel influenza A(H1N1) virus, little is as yet known about its transmission efficiency in close contact places such as households, schools, and workplaces. These are widely believed to be key in supporting propagating spread, and it is therefore of importance to assess the transmission levels of the virus in such settings. Methodology/Principal Findings We estimate the transmissibility of novel influenza A(H1N1) in 47 households in the Netherlands using stochastic epidemic models. All households contained a laboratory confirmed index case, and antiviral drugs (oseltamivir) were given to both the index case and other households members within 24 hours after detection of the index case. Among the 109 household contacts there were 9 secondary infections in 7 households. The overall estimated secondary attack rate is low (0.075, 95%CI: 0.037–0.13). There is statistical evidence indicating that older persons are less susceptible to infection than younger persons (relative susceptibility of older persons: 0.11, 95%CI: 0.024–0.43. Notably, the secondary attack rate from an older to a younger person is 0.35 (95%CI: 0.14–0.61) when using an age classification of ≤12 versus >12 years, and 0.28 (95%CI: 0.12–0.50) when using an age classification of ≤18 versus >18 years. Conclusions/Significance Our results indicate that the overall household transmission levels of novel influenza A(H1N1) in antiviral-treated households were low in the early stage of the epidemic. The relatively high rate of adult-to-child transmission indicates that control measures focused on this transmission route will be most effective in minimizing the total number of infections.
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Affiliation(s)
- Michiel van Boven
- Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, The Netherlands.
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