Publications
160 results found
Jafari H, Deshpande JM, Sutter RW, et al., 2014, Efficacy of inactivated poliovirus vaccine in India, Science, Vol: 345, Pages: 922-925, ISSN: 0036-8075
Inactivated poliovirus vaccine (IPV) is efficacious against paralytic disease, but its effect on mucosal immunity is debated. We assessed the efficacy of IPV in boosting mucosal immunity. Participants received IPV, bivalent 1 and 3 oral poliovirus vaccine (bOPV), or no vaccine. A bOPV challenge was administered 4 weeks later, and excretion was assessed 3, 7, and 14 days later. Nine hundred and fifty-four participants completed the study. Any fecal shedding of poliovirus type 1 was 8.8, 9.1, and 13.5% in the IPV group and 14.4, 24.1, and 52.4% in the control group by 6- to 11-month, 5-year, and 10-year groups, respectively (IPV versus control: Fisher’s exact test P < 0.001). IPV reduced excretion for poliovirus types 1 and 3 between 38.9 and 74.2% and 52.8 and 75.7%, respectively. Thus, IPV in OPV-vaccinated individuals boosts intestinal mucosal immunity.
Blake IM, Martin R, Goel A, et al., 2014, The role of older children and adults in wild poliovirus transmission, Proceedings of the National Academy of Sciences of the United States of America, Vol: 111, Pages: 10604-10609, ISSN: 0027-8424
As polio eradication inches closer, the absence of poliovirus circulation in most of the world and imperfect vaccination coverage are resulting in immunity gaps and polio outbreaks affecting adults. Furthermore, imperfect, waning intestinal immunity among older children and adults permits reinfection and poliovirus shedding, prompting calls to extend the age range of vaccination campaigns even in the absence of cases in these age groups. The success of such a strategy depends on the contribution to poliovirus transmission by older ages, which has not previously been estimated. We fit a mathematical model of poliovirus transmission to time series data from two large outbreaks that affected adults (Tajikistan 2010, Republic of Congo 2010) using maximum-likelihood estimation based on iterated particle-filtering methods. In Tajikistan, the contribution of unvaccinated older children and adults to transmission was minimal despite a significant number of cases in these age groups [reproduction number, R = 0.46 (95% confidence interval, 0.42–0.52) for >5-y-olds compared to 2.18 (2.06–2.45) for 0- to 5-y-olds]. In contrast, in the Republic of Congo, the contribution of older children and adults was significant [R = 1.85 (1.83–4.00)], perhaps reflecting sanitary and socioeconomic variables favoring efficient virus transmission. In neither setting was there evidence for a significant role of imperfect intestinal immunity in the transmission of poliovirus. Bringing the immunization response to the Tajikistan outbreak forward by 2 wk would have prevented an additional 130 cases (21%), highlighting the importance of early outbreak detection and response.
Mangal TD, Aylward RB, Grassly NC, 2014, Integration, community engagement, and polio eradication in Nigeria Reply, LANCET GLOBAL HEALTH, Vol: 2, Pages: E316-E316, ISSN: 2214-109X
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- Citations: 1
Mangal TD, Aylward RB, Mwanza M, et al., 2014, Key issues in the persistence of poliomyelitis in Nigeria: a case-control study, The Lancet Global Health, Vol: 2, Pages: E90-E97, ISSN: 2214-109X
BackgroundThe completion of poliomyelitis eradication is a global emergency for public health. In 2012, more than 50% of the world's cases occurred in Nigeria following an unanticipated surge in incidence. We aimed to quantitatively analyse the key factors sustaining transmission of poliomyelitis in Nigeria and to calculate clinical efficacy estimates for the oral poliovirus vaccines (OPV) currently in use.MethodsWe used acute flaccid paralysis (AFP) surveillance data from Nigeria collected between January, 2001, and December, 2012, to estimate the clinical efficacies of all four OPVs in use and combined this with vaccination coverage to estimate the effect of the introduction of monovalent and bivalent OPV on vaccine-induced serotype-specific population immunity. Vaccine efficacy was determined using a case-control study with CIs based on bootstrap resampling. Vaccine efficacy was also estimated separately for north and south Nigeria, by age of the children, and by year. Detailed 60-day follow-up data were collected from children with confirmed poliomyelitis and were used to assess correlates of vaccine status. We also quantitatively assessed the epidemiology of poliomyelitis and programme performance and considered the reasons for the high vaccine refusal rate along with risk factors for a given local government area reporting a case.FindingsAgainst serotype 1, both monovalent OPV (median 32·1%, 95% CI 26·1–38·1) and bivalent OPV (29·5%, 20·1–38·4) had higher clinical efficacy than trivalent OPV (19·4%, 16·1–22·8). Corresponding data for serotype 3 were 43·2% (23·1–61·1) and 23·8% (5·3–44·9) compared with 18·0% (14·1–22·1). Combined with increases in coverage, this factor has boosted population immunity in children younger than age 36 months to a record high (64–69% against serotypes 1 and 3). Vacci
Li LM, Grassly NC, Fraser C, 2014, Genomic analysis of emerging pathogens: methods, application and future trends, GENOME BIOLOGY, Vol: 15, ISSN: 1474-760X
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- Citations: 19
Mangal TD, Aylward RB, Grassly NC, 2013, The Potential Impact of Routine Immunization with Inactivated Poliovirus Vaccine on Wild-type or Vaccine-derived Poliovirus Outbreaks in a Posteradication Setting, AMERICAN JOURNAL OF EPIDEMIOLOGY, Vol: 178, Pages: 1579-1587, ISSN: 0002-9262
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- Citations: 18
Grassly NC, 2013, The final stages of the global eradication of poliomyelitis, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 368, ISSN: 0962-8436
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- Citations: 56
Doddington BJ, Bosch J, Oliver JA, et al., 2013, Context-dependent amphibian host population response to an invading pathogen, ECOLOGY, Vol: 94, Pages: 1795-1804, ISSN: 0012-9658
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- Citations: 54
Koukounari A, Moustaki I, Grassly NC, et al., 2013, Using a Nonparametric Multilevel Latent Markov Model to Evaluate Diagnostics for Trachoma, American Journal of Epidemiology, Vol: 177, Pages: 913-922, ISSN: 0002-9262
In disease control or elimination programs, diagnostics are essential for assessing the impact of interventions, refining treatment strategies, and minimizing the waste of scarce resources. Although high-performance tests are desirable, increased accuracy is frequently accompanied by a requirement for more elaborate infrastructure, which is often not feasible in the developing world. These challenges are pertinent to mapping, impact monitoring, and surveillance in trachoma elimination programs. To help inform rational design of diagnostics for trachoma elimination, we outline a nonparametric multilevel latent Markov modeling approach and apply it to 2 longitudinal cohort studies of trachoma-endemic communities in Tanzania (2000–2002) and The Gambia (2001–2002) to provide simultaneous inferences about the true population prevalence of Chlamydia trachomatis infection and disease and the sensitivity, specificity, and predictive values of 3 diagnostic tests for C. trachomatis infection. Estimates were obtained by using data collected before and after mass azithromycin administration. Such estimates are particularly important for trachoma because of the absence of a true “gold standard” diagnostic test for C. trachomatis. Estimated transition probabilities provide useful insights into key epidemiologic questions about the persistence of disease and the clearance of infection as well as the required frequency of surveillance in the postelimination setting.
O'Reilly KM, Durry E, ul Islam O, et al., 2012, The effect of mass immunisation campaigns and new oral poliovirus vaccines on the incidence of poliomyelitis in Pakistan and Afghanistan, 2001-11: a retrospective analysis, LANCET, Vol: 380, Pages: 491-498, ISSN: 0140-6736
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- Citations: 46
Grassly NC, Jafari H, Bahl S, et al., 2012, Waning Intestinal Immunity After Vaccination With Oral Poliovirus Vaccines in India, JOURNAL OF INFECTIOUS DISEASES, Vol: 205, Pages: 1554-1561, ISSN: 0022-1899
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- Citations: 54
Hird TR, Grassly NC, 2012, Systematic Review of Mucosal Immunity Induced by Oral and Inactivated Poliovirus Vaccines against Virus Shedding following Oral Poliovirus Challenge, PLOS PATHOGENS, Vol: 8, ISSN: 1553-7366
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- Citations: 146
Solomon AW, Engels D, Bailey RL, et al., 2012, A Diagnostics Platform for the Integrated Mapping, Monitoring and Surveillance of Neglected Tropical Diseases: Rationale and Target Product Profiles, PLoS Neglected Tropical Diseases
Marsh KA, Nyamukapa CA, Donnelly CA, et al., 2011, Monitoring trends in HIV prevalence among young people, aged 15 to 24 years, in Manicaland, Zimbabwe, Journal of the International AIDS Society, Vol: 14, ISSN: 1758-2652
O'Reilly KM, Chauvin C, Aylward RB, et al., 2011, A statistical model of the international spread of wild poliovirus in Africa used to predict and prevent outbreaks, PLoS Med, Vol: 8, Pages: 1-10, ISSN: 1549-1676
BACKGROUND: Outbreaks of poliomyelitis in African countries that were previously free of wild-type poliovirus cost the Global Polio Eradication Initiative US$850 million during 2003-2009, and have limited the ability of the program to focus on endemic countries. A quantitative understanding of the factors that predict the distribution and timing of outbreaks will enable their prevention and facilitate the completion of global eradication. METHODS AND FINDINGS: Children with poliomyelitis in Africa from 1 January 2003 to 31 December 2010 were identified through routine surveillance of cases of acute flaccid paralysis, and separate outbreaks associated with importation of wild-type poliovirus were defined using the genetic relatedness of these viruses in the VP1/2A region. Potential explanatory variables were examined for their association with the number, size, and duration of poliomyelitis outbreaks in 6-mo periods using multivariable regression analysis. The predictive ability of 6-mo-ahead forecasts of poliomyelitis outbreaks in each country based on the regression model was assessed. A total of 142 genetically distinct outbreaks of poliomyelitis were recorded in 25 African countries, resulting in 1-228 cases (median of two cases). The estimated number of people arriving from infected countries and <5-y childhood mortality were independently associated with the number of outbreaks. Immunisation coverage based on the reported vaccination history of children with non-polio acute flaccid paralysis was associated with the duration and size of each outbreak, as well as the number of outbreaks. Six-month-ahead forecasts of the number of outbreaks in a country or region changed over time and had a predictive ability of 82%. CONCLUSIONS: Outbreaks of poliomyelitis resulted primarily from continued transmission in Nigeria and the poor immunisation status of populations in neighbouring countries. From 1 January 2010 to 30 June 2011, reduced transmission in Nigeria and in
Gambhir M, Basanez MG, Blake IM, et al., 2010, Modelling trachoma for control programmes, Modelling Parasite Transmission and Control, Editors: Michael, Spear, Publisher: Austin, Texas: Landes Bioscience, ISBN: 9781441960641
Blake IM, Burton MJ, Solomon AW, et al., 2010, Targeting Antibiotics to Households for Trachoma Control, PLOS NEGLECTED TROPICAL DISEASES, Vol: 4, ISSN: 1935-2735
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- Citations: 16
Jenkins HE, Aylward RB, Gasasira A, et al., 2010, Implications of a Circulating Vaccine-Derived Poliovirus in Nigeria., NEW ENGLAND JOURNAL OF MEDICINE, Vol: 362, Pages: 2360-2369, ISSN: 0028-4793
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- Citations: 103
Grassly NC, Jafari H, Bahl S, et al., 2010, Asymptomatic Wild-Type Poliovirus Infection in India among Children with Previous Oral Poliovirus Vaccination, JOURNAL OF INFECTIOUS DISEASES, Vol: 201, Pages: 1535-1543, ISSN: 0022-1899
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- Citations: 38
Gambhir M, Basanez M-G, Blake IM, et al., 2010, Modelling Trachoma for Control Programmes, MODELLING PARASITE TRANSMISSION AND CONTROL, Vol: 673, Pages: 141-156, ISSN: 0065-2598
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- Citations: 6
Ribas L, Li MS, Doddington BJ, et al., 2009, Expression Profiling the Temperature-Dependent Amphibian Response to Infection by Batrachochytrium dendrobatidis, PLOS One, Vol: 4, ISSN: 1932-6203
Amphibians are experiencing a panzootic of unprecedented proportions caused by the emergence of Batrachochytrium dendrobatidis (Bd). However, all species are not equally at risk of infection, and risk is further modified by environmental variables, specifically temperature. In order to understand how, and when, hosts mount a response to Bd we analysed infection dynamics and patterns of gene expression in the model amphibian species Silurana (Xenopus) tropicalis. Mathematical modelling of infection dynamics demonstrate the existence of a temperature-dependent protective response that is largely independent of the intrinsic growth-rate of Bd. Using temporal expression-profiling by microarrays and qRT-PCR, we characterise this response in the main amphibian lymphoid tissue, the spleen. We demonstrate that clearance of Bd at the host-optimal temperature is not clearly associated with an adaptive immune response, but rather is correlated with the induction of components of host innate immunity including the expression of genes that are associated with the production of the antimicrobial skin peptide preprocareulein (PPCP) as well as inflammatory responses. We find that adaptive immunity appears to be lacking at host-optimal temperatures. This suggests that either Bd does not stimulate, or suppresses, adaptive immunity, or that trade-offs exist between innate and adaptive limbs of the amphibian immune system. At cold temperatures, S. tropicalis loses the ability to mount a PPCP-based innate response, and instead manifests a more pronounced inflammatory reaction that is characterised by the production of proteases and higher pathogen burdens. This study demonstrates the temperature-dependency of the amphibian response to infection by Bd and indicates the influence that changing climates may exert on the ectothermic host response to pathogens.
Grassly NC, Jafari H, Bahl S, et al., 2009, Mucosal Immunity after Vaccination with Monovalent and Trivalent Oral Poliovirus Vaccine in India, JOURNAL OF INFECTIOUS DISEASES, Vol: 200, Pages: 794-801, ISSN: 0022-1899
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- Citations: 52
Fraser C, Donnelly CA, Cauchemez S, et al., 2009, Influenza: Making Privileged Data Public Response, SCIENCE, Vol: 325, Pages: 1072-1073, ISSN: 0036-8075
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- Citations: 2
Fraser C, Donnelly CA, Cauchemez S, et al., 2009, Pandemic Potential of a Strain of Influenza A (H1N1): Early Findings, SCIENCE, Vol: 324, Pages: 1557-1561, ISSN: 0036-8075
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- Citations: 1393
Gambhir M, Basanez M-G, Burton MJ, et al., 2009, The Development of an Age-Structured Model for Trachoma Transmission Dynamics, Pathogenesis and Control, PLOS Neglected Tropical Diseases, Vol: 3, ISSN: 1935-2735
Background: Trachoma, the worldwide leading infectious cause of blindness, is due to repeated conjunctival infection with Chlamydia trachomatis. The effects of control interventions on population levels of infection and active disease can be promptly measured, but the effects on severe ocular sequelae require long-term monitoring. We present an age-structured mathematical model of trachoma transmission and disease to predict the impact of interventions on the prevalence of blinding trachoma.Methodology/Principal Findings: The model is based on the concept of multiple reinfections leading to progressive conjunctival scarring, trichiasis, corneal opacity and blindness. It also includes aspects of trachoma natural history, such as an increasing rate of recovery from infection and a decreasing chlamydial load with subsequent infections that depend upon a (presumed) acquired immunity that clears infection with age more rapidly. Parameters were estimated using maximum likelihood by fitting the model to pre-control infection prevalence data from hypo-, meso- and hyperendemic communities from The Gambia and Tanzania. The model reproduces key features of trachoma epidemiology: 1) the age-profile of infection prevalence, which increases to a peak at very young ages and declines at older ages; 2) a shift in this prevalence peak, toward younger ages in higher force of infection environments; 3) a raised overall profile of infection prevalence with higher force of infection; and 4) a rising profile, with age, of the prevalence of the ensuing severe sequelae (trachomatous scarring, trichiasis), as well as estimates of the number of infections that need to occur before these sequelae appear.Conclusions/Significance: We present a framework that is sufficiently comprehensive to examine the outcomes of the A (antibiotic) component of the SAFE strategy on disease. The suitability of the model for representing population-level patterns of infection and disease sequelae is discussed in
Blake IM, Burton MJ, Bailey RL, et al., 2009, Estimating Household and Community Transmission of Ocular <i>Chlamydia trachomatis</i>, PLOS NEGLECTED TROPICAL DISEASES, Vol: 3, ISSN: 1935-2735
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- Citations: 38
Grassly NC, Ward ME, Ferris S, et al., 2008, The Natural History of Trachoma Infection and Disease in a Gambian Cohort with Frequent Follow-Up, PLOS NEGLECTED TROPICAL DISEASES, Vol: 2, ISSN: 1935-2735
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- Citations: 67
Jenkins HE, Aylward RB, Gasasira A, et al., 2008, Effectiveness of immunization against paralytic poliomyelitis in Nigeria, NEW ENGLAND JOURNAL OF MEDICINE, Vol: 359, Pages: 1666-U111, ISSN: 0028-4793
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- Citations: 45
Grassly NC, Fraser C, 2008, Mathematical models of infectious disease transmission, NATURE REVIEWS MICROBIOLOGY, Vol: 6, Pages: 477-487, ISSN: 1740-1526
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- Citations: 351
Cooper A, Grassly N, Rambaut A, 2007, Using Molecular Data to Estimate Divergence Times, Palaeobiology II, Pages: 532-534, ISBN: 9780632051496
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- Citations: 1
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