The study objective was to evaluate the effects of vaccination (respiratory and clostridial vaccination or no vaccination) and deworming (fenbendazole and levamisole or no deworming) of high risk stocker calves on-arrival on health and growth performance. Eighty sale barn origin calves were purchased three separate years (n=240) from local order buyer. Steers (n=61) and bulls (n=179) were received over three days (d -3 to -1). On d 0 calves were stratified by arrival BW and FEC into 20 pens of 4 calves each, and treatment was applied to pens in 2 x 2 factorial. Vaccination increased the likelihood of BRD 1.7 times (P=0.07) versus calves not vaccinated. Vaccination did not affect gain, but calves receiving dewormer had greater ADG than those not receiving dewormer. Calves that arrived uncastrated or with high fever (≥40.0°C) gained less and were 1.7 and 4.3 times more likely (P<0.10) to be treated for disease, respectively.

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Introduction: Pediatric health care settings are high risk environments for spreading communicable and vaccine preventable diseases from health care workers to susceptible patients. Methods: All managers of pediatric clinics operating in the state of Utah were included. Participants were invited to complete a two-page questionnaire regarding their clinic vaccination policies. Results: Half (n = 23, 50%) of Utah pediatric outpatient clinics recommend employee vaccinations, although employee refusal is allowed without consequence. Of all adult vaccines, influenza was most often included as part of the employee vaccination policy. Some clinics required unvaccinated employees to wear masks in the event of illness, but many had no additional requirements for unvaccinated and ill employees. Discussion: Vaccination of health care workers is an effective approach to reduce disease transmission. Mandatory vaccination policies can significantly improve vaccination rates among health care workers.

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

<p>The main body of this thesis deals with three related concepts pertaining to vaccination strategies for childhood infectious disease. Chapter 2 deals with the implications of reversion in the Oral Polio Vaccine on global polio eradication programs. Chapter 3 explores the phenomenon of contact or secondary vaccination in the use of live-attenuated virus vaccines. Chapter 4 explores the importance of demographic stochasticity in pulse vaccination campaigns. largely focusing on measles dynamics. Abstracts for each chapter are given below.</p><p>Poliomyelitis vaccination via live Oral Polio Vaccine (OPV) suffers from the inherent problem of reversion: the vaccine may, upon replication in the human gut, mutate back to virulence and transmissibility resulting in circulating vaccine derived polio viruses (cVDPVs). We formulate a general mathematical model to assess the impact of cVDPVs on prospects for polio eradication. We find that for OPV coverage levels below a certain threshold, cVDPVs have a small impact in comparison to the expected endemic level of the disease in the absence of reversion. Above this threshold, the model predicts a small but significant endemic level of the disease, even where standard models predict eradication. In light of this, we consider and analyze three alternative eradication strategies involving a transition from continuous OPV vaccination to either continuous Inactivated Polio Vaccine (IPV), pulsed OPV vaccination, or a one-time IPV pulse vaccination. Stochastic modeling shows continuous IPV vaccination is effective at achieving eradication for moderate coverage levels, while pulsed OPV is effective if higher coverage levels are maintained. The one-time pulse IPV method may also be a viable strategy, especially in terms of the number of vaccinations required and time to eradication, provided that a sufficiently large pulse is practically feasible. More investigation is needed rq?;arding the frequency of revertant virus infection resulting directly from vaccination, the ability of IPV to induce gut immunity, and the potential role of spatial transmission dynamics in eradication efforts.</p> <p>Viruses contained in live-attenuated vims vaccines (LAVV) can be transmitted between individuals, resulting in secondary or contact vaccinations. This fact has been exploited successfully in the use of the Oral Polio Vaccine (OPV) to better control wild polio viruses. In this work we analyze general LAVV vaccination models for infections that confer lifelong immunity. We consider both standard (continuous) vaccination strategies and pulse vaccination programs (where mass vaccination is carried out at regular intervals). For continuous vaccination, we provide a complete global analysis of a very general compartmental ordinary differential equation LAVV model. We find that the threshold vaccination level required for eradication of wild virus depends on the basic reproduction numbers of both the wild and vaccine viruses, but is otherwise independent of the distributions of the durations in each of the sequence of stages of disease progression (e.g., latent, infectious, etc.). Furthermore, even for vaccine viruses with reproduction numbers below one. which would naturally fade from the population upon cessation of vaccination, there can be a significant reduction in the threshold vaccination level. The dependence of the threshold vaccination level on the virus reproduction numbers largely generalizes to the pulse vaccination model. For shorter pulsing periods there is negligible difference in threshold vaccination level as compared to continuous vaccination campaigns. Thus, we conclude that current policy in many countries to employ annual pulsed OPV vaccination does not significantly diminish the benefits of contact vaccination.</p><p> In the last two decades, many countries have implemented pulse vaccination for infectious diseases (mass vaccination campaigns repeated annually or at other regular intervals). Based on deterministic mathematical models, previous work has shown that the total expected cost of control or eradication (measured by the number of vaccine doses required) is identical for pulse vaccination (with any pulse interval) and for traditional, continuous vaccination. We reconsider this problem using stochastic epidemic models (both by direct simulation and by employing a moment closure approximation). We focus on measles and show that demographic stochasticity has a large impact on the relative success of pulse and continuous vaccination programs, even for well-mixed populations as large as 10 million.</p> / Thesis / Doctor of Philosophy (PhD)

Objectifs : Dans plusieurs pays la couverture vaccinale contre les virus du papillome humain (VPH) est associée aux déterminants sociaux des comportements sexuels et la participation au dépistage du cancer du col utérin. Ces vaccins protègent uniquement contre certains types de VPH, donc leur impact futur sur les VPH nonvaccinaux demeure incertain. L’hétérogénéité comportementale entre individus et biologique entre types de VPH affectera l’efficacité populationnelle de la vaccination contre les VPH. Les objectifs spécifiques de cette thèse étaient 1) de modéliser comment une couverture vaccinale inégale entre filles préadolescentes qui différeront selon leur activité sexuelle et leur participation au dépistage du cancer du col affectera l’efficacité populationnelle de la vaccination, 2) faire une synthèse et comparer les estimés d’efficacité croisée des vaccins contre les VPH dans des populations ADN-négatives aux VPH et 3) d’identifier, avec la modélisation, les devis d’étude épidémiologique qui réduisent les biais dans l’estimation des interactions biologiques entre types de VPH. Méthode : Nous avons utilisé des modèles de transmission dynamique et une revue systématique de la littérature pour répondre aux objectifs. 1) Nous avons modélisé une couverture vaccinale inégale entre filles qui différeront selon leur activité sexuelle et leur participation au dépistage, et examiné les changements postvaccination dans l’inégalité dans la prévalence des VPH et l’incidence des carcinomes malpighien (SCC) du col de l’utérus entre femmes ayant différents comportements. 2) Nous avons effectué une revue systématique et méta-analyse des efficacités croisées des vaccins contre les VPH estimées dans des populations ADNnégatives aux VPH. 3) Nous avons développé des modèles de transmission dynamique et d’interaction de deux types de VPH pour simuler les études épidémiologiques d’interactions entre les VPH. Résultats : Pour l’objectif 1), notre modèle de transmission prédit que l’efficacité populationnelle du vaccin dépendra de la distribution du vaccin dans la population. Après la vaccination, les inégalités absolues dans l’incidence de l’infection et des SCC entre groupes de femmes qui diffèrent selon leur activité sexuelle et leur participation au dépistage devraient diminuer. Inversement, les inégalités relatives pourraient augmenter si les femmes plus sexuellement actives et celles qui ne se font jamais dépister ont une couverture vaccinale moins élevée que les autres. Le taux d’incidence des SCC demeurera élevé chez les femmes qui ne sont jamais dépistées après la vaccination. L’efficacité croisée vaccinale et les interactions biologiques entre VPH ne sont pas encore assez bien caractérisées pour pouvoir prédire l’impact du vaccin sur les types de VPH nonvaccinaux. Pour l’objectif 2), notre méta-analyse des essais cliniques des vaccins suggère que le vaccin bivalent a une efficacité croisée significativement plus élevée que le quadrivalent contre les infections persistantes et lésions précancéreuses avec les VPH-31, 33 et 45. Les essais cliniques plus longs estiment une efficacité croisée plus faible. La modélisation des études épidémiologiques d’interactions pour l’objectif 3) montre que l’estimation des interactions biologiques entre types de VPH dans les études épidémiologiques est systématiquement biaisée par la corrélation entre le temps à risque d’infection avec un type de VPH et le temps à risque d’infection avec d’autres types de VPH. L’ajustement pour des marqueurs d’activité sexuelle ne réussit pas à contrôler ce biais. Une mesure valide des interactions biologiques entre types de VPH peut être obtenue uniquement avec des études épidémiologiques prospectives qui restreignent les analyses à des individus susceptibles ayant des partenaires sexuels infectés. Conclusion : L’hétérogénéité comportementale entre individus et l’hétérogénéité biologique entre VPH affecteront l’efficacité populationnelle du vaccin contre les VPH. Dans les contextes où les déterminants sociaux des comportements sexuels et la participation au dépistage sont aussi associés à la couverture vaccinale chez les préadolescentes, l’inégalité relative dans l’incidence des SCC risque d’augmenter. Ces comportements demeureront des facteurs de risque importants du cancer du col à l’avenir. L’effet à long terme du vaccin sur les types de VPH non-vaccinaux demeure incertain. Quoique nos résultats suggèrent que les vaccins offrent une efficacité croisée contre certains types de VPH, celle-ci pourrait diminuer après quelques années. Des interactions compétitives entre VPH pourraient exister malgré les associations observées entre les incidences des infections VPH, donc une augmentation post-vaccination de la prévalence des VPH non-vaccinaux demeure possible. Des devis d’analyse plus complexes sont nécessaires pour mesurer de façon valide les interactions biologiques entre les VPH dans les études épidémiologiques. / Objective: In many countries, uptake of the human papillomavirus (HPV) vaccine is associated with many of the same social determinants as cervical cancer and its behavioural risk factors, most notably sexual activity and screening participation. HPV vaccines only protect against a handful of oncogenic HPV types, so their impact on non-vaccine HPV types is uncertain. This behavioural heterogeneity between individuals and biological heterogeneity between HPV types will affect the population-level impact of HPV vaccination. The specific objectives were to 1) model how differential vaccine uptake between preadolescent girls who will have different sexual and cervical cancer screening behaviours can affect vaccination effectiveness, 2) review and compare estimates of HPV vaccine cross-efficacy in HPV-negative populations, and 3) use transmission modelling to identify the epidemiological study designs which reduce bias in the estimation of biological interactions between HPV types. Methods: We used transmission dynamic models and a systematic review of the literature to address these objectives. 1) We modeled different vaccine uptakes between preadolescent girls who will have different sexual and cervical cancer screening behaviours, and examined the predicted post-vaccination changes in inequalities in the prevalence of HPV and the incidence of cervical squamous cell carcinomas (SCC) between women with different behaviours. 2) We performed a systematic review and meta-analysis of HPV vaccine cross-efficacy in HPV-negative populations. 3) We developed dynamic transmission models of two HPV types to simulate epidemiological studies of biological interactions between HPV types. Results: For objective 1), our transmission dynamic model predicts that the population-level effectiveness of HPV vaccines will depend on its uptake distribution in the population. Absolute inequalities in the prevalence of infection and the incidence of SCC between women with different sexual and screening behaviours should diminish following vaccination. Inversely, relative inequalities between these women could increase if those who are more sexually active and who are never screened also have the lowest vaccine uptake. The incidence rate of SCC will remain high in women who are never screened post-vaccination. HPV vaccines’ cross-efficacy and the biological interactions between HPV types were not sufficiently quantified to allow predicting the impact of HPV vaccination on non-vaccine HPV types. For objective 2), our meta-analysis of vaccine clinical trials suggest that the bivalent vaccine has a significantly higher efficacy than the quadrivalent vaccine against infections and lesions with HPV-31, 33, and 45. Longer clinical trials estimate lower cross-efficacies. The simulation of epidemiological studies for objective 3) revealed that the estimation of biological interactions between HPV types in epidemiological studies is systematically biased by the correlation between the times at-risk for infection with different HPV types, which results in a cross-sectional and prospective correlation between their infection incidences. Adjusting for sexual behaviour markers does not control this bias. A valid measure of biological interactions between HPV types can only be obtained in prospective epidemiological studies which restrict analyses to times where individuals have an infected partner and thus are at-risk of infection. Conclusions: Behavioural heterogeneity between individuals and biological heterogeneity between HPV types will affect the population-level impact of HPV vaccination and should be considered in mathematical models and epidemiological studies. In contexts where the social determinants of sexual activity and screening are also associated with vaccine uptake in preadolescent girls, relative health inequalities may increase. These behaviours will remain important risk factors for cervical cancer in the vaccine era. The long-term effect of HPV vaccines on non-vaccine HPV types remains uncertain. While our results suggest that vaccines offer crossefficacy against certain HPV types, this cross-efficacy could wane within a few years. Competitive interactions between HPV types could exist despite observed associations between the incidences of different HPV type infections, so a post-vaccination increase in non-vaccine HPV types remains possible. More complex analysis designs are required to validly measure biological interactions between HPV types in epidemiological studies.

Human papillomavirus (HPV) is a sexually transmitted disease that often presents as genital warts, but may also lead to cancers, including those of the vagina, penis, mouth and tonsils. Despite three vaccines being currently available to prevent HPV, the HPV vaccine retains a low national average vaccination rate when compared to the Tetanus-Diptheria- Pertussis (Tdap) vaccine. Considering the need for improvement it is important to identify factors that may be contributing to this low national immunization rate, one of them being parental race. The purpose of this literature review is to identify whether race affects parents' intent to vaccinate their children against HPV. A database search of CINAHL Plus with Full Text, MEDLINE, and PsycINFO was conducted and a total of 13 articles were reviewed based on the relevance to the purpose of the literature review. While racial differences were noted, there were other factors that also affect a parent's intent to vaccinate their children against HPV. There is more research to be done when looking at how race may independently affect a parent's intent to vaccinate their children against HPV.

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