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Background: Worldwide, countries are examining whether to implement 1-dose human papillomavirus (HPV) vaccination instead of using 2 doses. To inform policy, we sought to project the population-level impact and efficiency of switching from 2-dose to 1-dose gender-neutral routine HPV vaccination in Canada. Methods: We used HPV-ADVISE, an individual-based transmission-dynamic model of HPV infections and diseases, to mathematically model vaccination programs in 2 provinces, Quebec, a province with high HPV vaccination coverage (around 85%), and Ontario, which has lower coverage (around 65%). We examined non-inferior and pessimistic scenarios of the efficacy (vaccine efficacy of 98% or 90%) and average vaccine duration (lifelong, 30 yr, or 25 yr) of 1 dose compared with 2 doses (98% vaccine efficacy, lifelong vaccine duration). Our main outcomes were the relative reduction in HPV-16 (by sex) and cervical cancers, and the number of doses needed to prevent 1 cervical cancer. Results: Our model projected that 1-dose HPV vaccination would avert a similar number of cervical cancers as 2 doses in Canada, under various scenarios. Under the most pessimistic scenario (25-yr vaccine duration), 1-dose vaccination would avert fewer cervical cancers than 2 doses, by about 3 percentage points over 100 years. All 1-dose scenarios were projected to lead to elimination of cervical cancer (< 4 cervical cancers/100 000 female-years) and to be a substantially more efficient use of vaccine doses than a 2-dose scenario (1-dose v. no vaccination = 8001000 doses needed to prevent 1 cervical cancer; incremental doses for 2-dose v. 1-dose vaccination > 10 000 doses needed to prevent 1 additional cervical cancer). Interpretation: If the average duration of 1-dose protection is longer than 25 years, a 1-dose HPV vaccination program would protect those vaccinated during their peak ages of sexual activity and prevent a similar number of HPV-related cancers as a 2-dose program, while being a more efficient use of vaccine doses., In April 2022, the World Health Organization (WHO) Strategic Advisory Group of Experts on Immunization (SAGE) announced that human papillomavirus (HPV) vaccination with a single dose could be considered for [...]

Background: The speed of vaccine development has been a singular achievement during the COVID-19 pandemic, although uptake has not been universal. Vaccine opponents often frame their opposition in terms of the rights of the unvaccinated. We sought to explore the impact of mixing of vaccinated and unvaccinated populations on risk of SARS-CoV-2 infection among vaccinated people. Methods: We constructed a simple susceptible-infectious-recovered compartmental model of a respiratory infectious disease with 2 connected subpopulations: people who were vaccinated and those who were unvaccinated. We simulated a spectrum of pat terns of mixing between vaccinated and unvaccinated groups that ranged from random mixing to complete like-with-like mixing (complete assortativity), in which people have contact exclusively with others with the same vaccination status. We evaluated the dynamics of an epidemic within each subgroup and in the population as a whole. Results: We found that the risk of infection was markedly higher among unvaccinated people than among vaccinated people under all mixing assumptions. The contact-adjusted contribution of unvaccinated people to infection risk was disproportionate, with unvaccinated people contributing to infections among those who were vaccinated at a rate higher than would have been expected based on contact numbers alone. We found that as like-with-like mixing increased, attack rates among vaccinated people decreased from 15% to 10% (and increased from 62% to 79% among unvaccinated people), but the contact-adjusted contribution to risk among vaccinated people derived from contact with unvaccinated people increased. Interpretation: Although risk associated with avoiding vaccination during a virulent pandemic accrues chiefly to people who are unvaccinated, their choices affect risk of viral infection among those who are vaccinated in a manner that is disproportionate to the portion of unvaccinated people in the population., The remarkable speed of vaccine development, production and administration during the COVID-19 pandemic is a singular human achievement. (1) While the ability to vaccinate to herd immunity has been held [...]

Background: Between February and June 2021, the initial wild-type strains of SARS-CoV-2 were supplanted in Ontario, Canada, by new variants of concern (VOCs), first those with the N501Y mutation (i.e., Alpha/B1.1.17, Beta/B.1.351 and Gamma/P.1 variants) and then the Delta/B.1.617 variant. The increased transmissibility of these VOCs has been documented, but knowledge about their virulence is limited. We used Ontario's COVID-19 case data to evaluate the virulence of these VOCs compared with nonVOC SARS-CoV-2 strains, as measured by risk of hospitalization, intensive care unit (ICU) admission and death. Methods: We created a retrospective cohort of people in Ontario who tested positive for SARS-CoV-2 and were screened for VOCs, with dates of test report between Feb. 7 and June 27, 2021. We constructed mixed-effect logistic regression models with hospitalization, ICU admission and death as outcome variables. We adjusted models for age, sex, time, vaccination status, comorbidities and pregnancy status. We included health units as random intercepts. Results: Our cohort included 212 326 people. Compared with non-VOC SARS-CoV-2 strains, the adjusted elevation in risk associated with N501Y-positive variants was 52% (95% confidence interval [CI] 42%-63%) for hospitalization, 89% (95% CI 67%-117%) for ICU admission and 51% (95% CI 30%-78%) for death. Increased risk with the Delta variant was more pronounced at 108% (95% CI 78%-140%) for hospitalization, 235% (95% CI 160%-331%) for ICU admission and 133% (95% CI 54%-231%) for death. Interpretation: The increasing virulence of SARS-CoV-2 VOCs will lead to a considerably larger, and more deadly, pandemic than would have occurred in the absence of the emergence of VOCs., Novel SARS-CoV-2 variants of concern (VOCs), including viral lineages carrying the N501Y (Alpha/B.1.1.7) or both the N501Y and E484K mutations (Beta/B.1.351 and Gamma /P.1), were first identified in Ontario, Canada, [...]

CONTEXTE: Au Canada, on utilise des interventions d'eloignement physique pour ralentir la propagation du SRAS-CoV-2 (coronavirus du syndrome respiratoire aigu severe 2), mais on ignore au juste quelle en sera l'efficacite. Nous avons evalue comment differentes interventions non pharmacologiques pouvaient etre utilisees pour maTtriser la pandemie de COVID-19 (maladie a coronavirus 2019) et alleger le fardeau qu'elle impose au systeme de sante. METHODES: Nous avons utilise un modele a compartiments structure selon l'age pour faire une analyse de la transmission de la COVID-19 dans la population de l'Ontario, au Canada. Nous avons compare un scenario de reference, soit depistage limite, isolement et quarantaine, a des scenarios incluant depistage accru, mesures strictes d'eloignement physique, ou combinaison de depistage accru et d'eloignement physique moins strict. Les interventions etaient appliquees soit pendant des durees fixes, soit selon un cycle dynamique en fonction de l'occupation projetee des lits dans les unites de soins intensifs (USI). Nous presentons les medianes et les intervalles de credibilite tires de 100 experiences repliquees par scenario sur un horizon temporel de 2 ans. RESULTATS: Selon le scenario de reference, nous avons estime que 56 % (intervalle de credibilite de 95 %o, 42 %-63%) de la population ontarienne contractait l'infection pendant l'epidemie. Au moment du sommet epidemique, nous avons projete 107000 (intervalle de credibilite de 95 %, 60 760-149 000) hospitalisations (soins standards) et 55500 (intervalle de credibilite de 95 %, 32 700-75 200) hospitalisations dans les USI. Pour les scenarios a duree fixe, selon les projections, toutes les interventions retardaient et reduisaient la hauteur du sommet epidemique par rapport au scenario de reference, et ce sont les mesures d'eloignement physique strict qui exergaient le plus d'effet; de meme, les interventions de duree plus longue etaient plus efficaces. Selon les projections, les interventions dynamiques reduisaient la proportion de la population atteinte a la fin de la periode de 2 ans et pouvaient ramener le nombre median de cas dans les USI en dega des estimations actuelles de leur capacite en Ontario. INTERPRETATION: Sans eloignement physique substantiel ou une combinaison d'eloignement physique modere et de depistage accru, nous projetons que les ressources des USI pourraient etre insuffisantes. L'eloignement physique dynamique maintiendrait la capacite du systeme de sante en plus de donner un repit psychologique et economique periodique aux populations., La pandemie de COVID-19 (maladie a coronavirus 2019) represente une urgence mondiale de sante publique sans precedent dans l'histoire recente. Depuis le rapport initial de l'Organisation mondiale de la sante [...]

BACKGROUND: Physical-distancing interventions are being used in Canada to slow the spread of severe acute respiratory syndrome coronavirus 2, but it is not clear how effective they will be. We evaluated how different nonpharmaceutical interventions could be used to control the coronavirus disease 2019 (COVID-19) pandemic and reduce the burden on the health care system. METHODS: We used an age-structured compartmental model of COVID-19 transmission in the population of Ontario, Canada. We compared a base case with limited testing, isolation and quarantine to scenarios with the following: enhanced case finding, restrictive physical-distancing measures, or a combination of enhanced case finding and less restrictive physical distancing. Interventions were either implemented for fixed durations or dynamically cycled on and off, based on projected occupancy of intensive care unit (ICU) beds. We present medians and credible intervals from 100 replicates per scenario using a 2-year time horizon. RESULTS: We estimated that 56% (95% credible interval 42%-63%) of the Ontario population would be infected over the course of the epidemic in the base case. At the epidemic peak, we projected 107 000 (95% credible interval 60 760-149 000) cases in hospital (non-ICU) and 55 500 (95% credible interval 32 700-75 200) cases in ICU. For fixed-duration scenarios, all interventions were projected to delay and reduce the height of the epidemic peak relative to the base case, with restrictive physical distancing estimated to have the greatest effect. Longer duration interventions were more effective. Dynamic interventions were projected to reduce the proportion of the population infected at the end of the 2-year period and could reduce the median number of cases in ICU below current estimates of Ontario's ICU capacity. INTERPRETATION: Without substantial physical distancing or a combination of moderate physical distancing with enhanced case finding, we project that ICU resources would be overwhelmed. Dynamic physical distancing could maintain health-system capacity and also allow periodic psychological and economic respite for populations., The coronavirus disease 2019 (COVID-19) pandemic represents a global public health emergency unparalleled in recent time. In the 2 months since the initial World Health Organization report describing the COVID-19 [...]