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Modeling rotavirus strain dynamics in developed countries to understand the potential impact of vaccination on genotype distributions.

ABSTRACT: Understanding how immunity shapes the dynamics of multistrain pathogens is essential in determining the selective pressures imposed by vaccines. There is currently much interest in elucidating the strain dynamics of rotavirus to determine whether vaccination may lead to the replacement of vaccine-type strains. In developed countries, G1P[8] strains constitute the majority of rotavirus infections most years, but occasionally other genotypes dominate for reasons that are not well understood. We developed a mathematical model to examine the interaction of five common rotavirus genotypes. We explored a range of estimates for the relative strength of homotypic vs. heterotypic immunity and compared model predictions against observed genotype patterns from six countries. We then incorporated vaccination in the model to examine its impact on rotavirus incidence and the distribution of strains. Our model can explain the coexistence and cyclical pattern in the distribution of genotypes observed in most developed countries. The predicted frequency of cycling depends on the relative strength of homotypic vs. heterotypic immunity. Vaccination that provides strong protection against G1 and weaker protection against other strains will likely lead to an increase in the relative prevalence of non-G1 strains, whereas a vaccine that provides equally strong immunity against all strains may promote the continued predominance of G1. Overall, however, disease incidence is expected to be substantially reduced under both scenarios and remain below prevaccination levels despite the possible emergence of new strains. Better understanding of homotypic vs. heterotypic immunity, both natural and vaccine-induced, will be critical in predicting the impact of vaccination.

SUBMITTER: Pitzer VE

PROVIDER: S-EPMC3228484 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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Modeling rotavirus strain dynamics in developed countries to understand the potential impact of vaccination on genotype distributions.

Pitzer Virginia E VE Patel Manish M MM Lopman Ben A BA Viboud Cécile C Parashar Umesh D UD Grenfell Bryan T BT

Proceedings of the National Academy of Sciences of the United States of America 20111114 48

Understanding how immunity shapes the dynamics of multistrain pathogens is essential in determining the selective pressures imposed by vaccines. There is currently much interest in elucidating the strain dynamics of rotavirus to determine whether vaccination may lead to the replacement of vaccine-type strains. In developed countries, G1P[8] strains constitute the majority of rotavirus infections most years, but occasionally other genotypes dominate for reasons that are not well understood. We de ...[more]

PMID: 22084114

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Project description:BackgroundRotavirus incidence remains relatively high in low-income countries (LICs) compared to high-income countries (HICs) after vaccine introduction. Ghana introduced monovalent rotavirus vaccine in April 2012 and despite the high coverage, vaccine performance has been modest compared to developed countries. The predictors of low vaccine effectiveness in LICs are poorly understood, and the drivers of subnational heterogeneity in rotavirus vaccine impact are unknown.MethodsWe used mathematical models to investigate variations in rotavirus incidence in children <5 years old in Ghana. We fit models to surveillance and case-control data from three different hospitals: Korle-Bu Teaching Hospital in Accra, Komfo Anokye Teaching Hospital in Kumasi, and War Memorial Hospital in Navrongo. The models were fitted to both pre- and post-vaccine data to estimate parameters describing the transmission rate, waning of maternal immunity, and vaccine response rate.ResultsThe seasonal pattern and age distribution of rotavirus cases varied among the three study sites in Ghana. Our model was able to capture the spatio-temporal variations in rotavirus incidence across the three sites and showed good agreement with the age distribution of observed cases. The rotavirus transmission rate was highest in Accra and lowest in Navrongo, while the estimated duration of maternal immunity was longer (~5 months) in Accra and Kumasi and shorter (~3 months) in Navrongo. The proportion of infants who responded to the vaccine was estimated to be high in Accra and Kumasi and low in Navrongo.ConclusionsRotavirus vaccine impact varies within Ghana. A low vaccine response rate was estimated for Navrongo, where rotavirus is highly seasonal and incidence limited to a few months of the year. Our findings highlight the need to further explore the relationship between rotavirus seasonality, maternal immunity, and vaccine response rate to determine how they influence vaccine effectiveness and to develop strategies to improve vaccine impact.

Project description:BackgroundRotavirus infection is responsible for about 500,000 deaths annually, and the disease burden is disproportionately borne by children in low-income countries. Recently the World Health Organization (WHO) has released a global recommendation that all countries include infant rotavirus vaccination in their national immunization programs. Our objective was to provide information on the expected health, economic and financial consequences of rotavirus vaccines in the 72 GAVI support-eligible countries.MethodsWe synthesized population-level data from various sources (primarily from global-level databases) for the 72 countries eligible for the support by the GAVI Alliance (GAVI-eligible countries) in order to estimate the health and economic impact associated with rotavirus vaccination programs. The primary outcome measure was incremental cost (in 2005 international dollars [I$]) per disability-adjusted life year (DALY) averted. We also projected the expected reduction in rotavirus disease burden and financial resources required associated with a variety of scale-up scenarios.ResultsUnder the base-case assumptions (70% coverage), vaccinating one single birth cohort would prevent about 55% of rotavirus associated deaths in the 72 GAVI-eligible countries. Assuming I$25 per vaccinated child (approximately $5 per dose), the number of countries with the incremental cost per DALY averted less than I$200 was 47. Using the WHO's cost-effectiveness threshold based on per capita GDP, the vaccines were considered cost-effective in 68 of the 72 countries (approximately 94%). A 10-year routine rotavirus vaccination would prevent 0.9-2.8 million rotavirus associated deaths among children under age 5 in the poorest parts of the world, depending on vaccine scale-up scenarios. Over the same intervention period, rotavirus vaccination programs would also prevent 4.5-13.3 million estimated cases of hospitalization and 41-107 million cases of outpatient clinic visits in the same population.ConclusionsOur findings suggest that rotavirus vaccination would be considered a worthwhile investment for improving general development as well as childhood health level in most low-income countries, with a favorable cost-effectiveness profile even under a vaccine price ($1.5-$5.0 per dose) higher than those of traditional childhood vaccines.

Project description:Over the last 5 years, prophylactic vaccination against human papillomavirus (HPV) in pre-adolescent females has been introduced in most developed countries, supported by modeled evaluations that have almost universally found vaccination of pre-adolescent females to be cost-effective. Studies to date suggest that vaccination of pre-adolescent males may also be cost-effective at a cost per vaccinated individual of ~US$400-500 if vaccination coverage in females cannot be increased above ~50%; but if it is possible, increasing coverage in females appears to be a better return on investment. Comparative evaluation of the quadrivalent (HPV16,18,6,11) and bivalent (HPV16,18) vaccines centers around the potential trade-off between protection against anogenital warts and vaccine-specific levels of cross-protection against infections not targeted by the vaccines. Future evaluations will also need to consider the cost-effectiveness of a next generation nonavalent vaccine designed to protect against ~90% of cervical cancers. The timing of the effect of vaccination on cervical screening programs will be country-specific and will depend on vaccination catch-up age range and coverage and the age at which screening starts. Initial evaluations suggest that if screening remains unchanged, it will be less cost-effective in vaccinated compared to unvaccinated women but, in the context of current vaccines, will remain an important prevention method. Comprehensive evaluation of new approaches to screening will need to consider the population-level effects of vaccination over time. New screening strategies of particular interest include delaying the start age of screening, increasing the screening interval and switching to primary HPV screening. Future evaluations of screening will also need to focus on the effects of disparities in screening and vaccination uptake, the potential effects of vaccination on screening participation, and the effects of imperfect compliance with screening recommendations. This article forms part of a special supplement entitled "Comprehensive Control of HPV Infections and Related Diseases" Vaccine Volume 30, Supplement 5, 2012.

Project description:IntroductionRotavirus gastroenteritis (RVGE) remains a leading cause of hospitalization and death in children under five years of age in the Philippines. Rotavirus (RV) vaccination was introduced into the national immunization program (NIP) in 2012 but has since been limited to one region due to cost considerations and conflicting local cost-effectiveness estimates. Updated estimates of the cost-effectiveness of RV vaccination are required to inform prioritization of national immunization activities.MethodsWe calculated the potential costs and benefits of rotavirus vaccination over a 10-year-period (2021-2031) from a government and societal perspective, comparing four alternative rotavirus vaccines: Rotavac, Rotasiil, Rotarix and Rotateq. For each vaccine, a proportionate outcomes model was used to calculate the expected number of disease events, DALYs, vaccination program costs, and healthcare costs, with and without vaccination. The primary outcome measure was the cost per DALY averted. Assuming each product would generate similar benefits, the dominant (lowest cost) product was identified. We then calculated the cost-effectiveness (US$ per Disability Adjusted Life Year [DALY] averted) of the least costly product and compared it to willingness-to-pay thresholds of 0.5 and 1 times the national GDP per capita ($3,485), and ran deterministic and probabilistic sensitivity analyses.ResultsIntroducing any of the four rotavirus vaccines would avert around 40% of RVGE visits, hospitalizations, and deaths over the period 2021-2031. Over the same ten-year period, the incremental cost of vaccination from a government perspective was estimated to be around $104, $105, $220, and $277 million for Rotavac, Rotasiil, Rotarix and Rotateq, respectively. The equivalent cost from a societal perspective was $58, $60, $178 and $231 million. The cost-effectiveness of the least costly product (Rotavac) was $1,148 ($830-$1682) from a government perspective and $646 ($233-1277) from a societal perspective. All other products offered similar benefits but at a higher cost. There is a >99% probability that Rotavac would be cost-effective at a willingness-to-pay threshold set at 0.5 times the national GDP per capita.ConclusionBoth Rotavac and Rotasiil are likely to be cost-effective options in the Philippines, but it is not possible to say definitively which product should be preferred. Rotarix and Rotateq are expected to offer similar benefits at more cost, so would need to be priced far more competitively to be considered for introduction.

Project description:BackgroundThe majority of countries with the highest rotavirus-associated death rates are in sub-Saharan Africa. In 2009, the World Health Organization (WHO) recommended routine vaccination against rotavirus worldwide, with unique age recommendations to administer the first dose before 15 weeks of age and last dose by 32 weeks of age. These age restrictions were relaxed in January 2013, but they may still lead to lower rotavirus vaccine coverage.MethodsChildren age-eligible to have received rotavirus vaccine that were enrolled in Ghana, Zimbabwe, Rwanda or Burkina Faso's active rotavirus surveillance platforms from 2013 to 2017 and had a stool specimen that tested rotavirus-negative were included in the analysis. Proportion vaccinated and timeliness of rotavirus vaccine versus DTPw-HepB-Hib (pentavalent) first dose and last dose were compared at weeks 15 and 32, respectively, using Chi-square analyses. Odds ratios were calculated using logistic regression.ResultsAmong children who received rotavirus vaccine dose 1, 96-99% received this dose by 15 weeks of age and among children who received the last dose, 98-99% received it by 32 weeks of age. In all four countries, there was no significant difference in the proportion of children who received first dose rotavirus versus pentavalent vaccine by week 15, or last dose rotavirus versus concordant pentavalent vaccine by week 32. Delayed administration of first dose pentavalent vaccine was significantly associated with missing first dose of rotavirus vaccine in 3 of the 4 countries studied, although delays in administration were rare (1-4%).ConclusionsRotavirus vaccination was timely among sentinel sites in these four early rotavirus vaccine-introducing countries in Africa. Late presentation for vaccination may have resulted in some children with access to care missing first dose of rotavirus vaccine; however, vaccination delays were infrequent and therefore the potential impact of the age restrictions on overall proportion vaccinated was minimal.

Project description:BackgroundLimited data are available describing human papillomavirus (HPV) genotype distributions in cervical cancer in the United States. Such studies are needed to predict how HPV vaccination and HPV-based screening will influence cervical cancer prevention.MethodsWe used the New Mexico Surveillance, Epidemiology, and End Results Registry to ascertain cases of in situ (n = 1213) and invasive (n = 808) cervical cancer diagnosed during 1985-1999 and 1980-1999, respectively, in the state of New Mexico. HPV genotyping was performed using two polymerase chain reaction-based methods on paraffin-embedded tissues from in situ and invasive cancers and on cervical Papanicolaou test specimen from control subjects (ie, women aged 18-40 years attending clinics for routine cervical screening [n = 4007]). Relative risks for cervical cancer were estimated, and factors associated with age at cancer diagnosis and the prevalence of HPV genotypes in cancers were examined.ResultsThe most common HPV genotypes detected in invasive cancers were HPV type 16 (HPV16, 53.2%), HPV18 (13.1%), and HPV45 (6.1%) and those in in situ cancers were HPV16 (56.3%), HPV31 (12.6%), and HPV33 (8.0%). Invasive cancer case subjects who were positive for HPV16 or 18 were diagnosed at younger ages than those who were positive for other carcinogenic HPV genotypes (mean age at diagnosis: 48.1 [95% confidence interval {CI} = 46.6 to 49.6 years], 45.9 [95% CI = 42.9 to 49.0 years], and 52.3 years [95% CI = 50.0 to 54.6 years], respectively). The proportion of HPV16-positive in situ and invasive cancers, but not of HPV18-positive cancers, declined with more recent calendar year of diagnosis, whereas the proportion positive for carcinogenic HPV genotypes other than HPV18 increased.ConclusionsHPV16 and 18 caused the majority of invasive cervical cancer in this population sample of US women, but the proportion attributable to HPV16 declined over the last 20 years. The age at diagnosis of HPV16- and HPV18-related cancers was 5 years earlier than that of cancers caused by carcinogenic HPV genotypes other than HPV16 and 18, suggesting that the age at initiation of cervical screening could be delayed in HPV-vaccinated populations.

Dataset Information

Modeling rotavirus strain dynamics in developed countries to understand the potential impact of vaccination on genotype distributions.

Publications

Modeling rotavirus strain dynamics in developed countries to understand the potential impact of vaccination on genotype distributions.

Similar Datasets

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