ABSTRACT
Objectives: To describe time trends in social contacts of individuals according to comorbidity and vaccination status before and during the first three waves of the COVID-19 pandemic in Quebec, Canada. Design: Repeated cross-sectional population-based surveys. Setting: General population. Participants: Non-institutionalized adults from Quebec, Canada, recruited by random digit dialling before (2018/2019) and during the pandemic (April 2020 to July 2021). A total of 1441 and 5185 participants with and without comorbidities, respectively, were included in the analyses. Main outcome measures: Number of social contacts (two-way conversation at a distance [≤]2 meters or a physical contact, irrespective of masking) documented in a self-administered web-based questionnaire. We compared the mean number of contacts according to the comorbidity status of participants (pre-existing medical conditions with symptoms/medication in the past 12 months) and 1-dose vaccination status during the third wave. All analyses were performed using weighted generalized linear models with a Poisson distribution and robust variance. Results: Contacts significantly decreased from a mean of 6.1 (95% confidence interval 4.9 to 7.3) before the pandemic to 3.2 (2.5 to 3.9) during the first wave among individuals with comorbidities, and from 8.1 (7.3 to 9.0) to 2.7 (2.2 to 3.2) among individuals without comorbidities. Individuals with comorbidities maintained fewer contacts than those without comorbidities in the second wave, with a significant difference before the Christmas 2020/2021 holidays (2.9 (2.5 to 3.2) v 3.9 (3.5 to 4.3); P<0.001). During the third wave, contacts were similar for individuals with (4.1, 3.4 to 4.7) and without comorbidities (4.5, 4.1 to 4.9; P=0.27). This could be partly explained by individuals with comorbidities vaccinated with their first dose who increased their contacts to the level of those without comorbidities. Conclusions: The lower level of contacts maintained by individuals with comorbidities could have influenced the burden of hospitalisations and deaths of the second wave in Quebec. It will be important to closely monitor COVID-19-related outcomes and social contacts by comorbidity and vaccination status to inform targeted or population-based interventions.
Subject(s)
COVID-19ABSTRACT
Background The Canadian COVID-19 immunization strategy deferred second doses and allowed mixed schedules. We compared two-dose vaccine effectiveness (VE) by vaccine type (mRNA and/or ChAdOx1), interval between doses, and time since second dose in two of Canada's larger provinces. Methods Two-dose VE against infections and hospitalizations due to SARS-CoV-2, including variants of concern, was assessed between May 30 and October 2, 2021 using test-negative designs separately conducted among community-dwelling adults [≥]18-years-old in British Columbia (BC) and Quebec, Canada. Findings In both provinces, two doses of homologous or heterologous SARS-CoV-2 vaccines were associated with ~95% reduction in the risk of hospitalization. VE exceeded 90% against SARS-CoV-2 infection when at least one dose was an mRNA vaccine, but was lower at ~70% when both doses were ChAdOx1. Estimates were similar by age group (including adults [≥]70-years-old) and for Delta-variant outcomes. VE was significantly higher against both infection and hospitalization with longer 7-8-week vs. manufacturer-specified 3-4-week interval between doses. Two-dose mRNA VE was maintained against hospitalization for the 5-7-month monitoring period and while showing some decline against infection, remained [≥]80%. Interpretation Two doses of mRNA and/or ChAdOx1 vaccines gave excellent protection against hospitalization, with no sign of decline by 5-7 months post-vaccination. A 7-8-week interval between doses improved VE and may be optimal in most circumstances. Findings indicate prolonged two-dose protection and support the use of mixed schedules and longer intervals between doses, with global health, equity and access implications in the context of recent third-dose proposals.
Subject(s)
COVID-19ABSTRACT
ABSTRACT Background: Since the beginning of the Covid-19 pandemic, many countries, including Canada, have adopted unprecedented physical distancing measures such as closure of schools and non-essential businesses, and restrictions on gatherings and household visits. We described time trends in social contacts for the pre-pandemic and pandemic periods in Quebec, Canada. Methods: CONNECT is a population-based study of social contacts conducted shortly before (2018/2019) and during the Covid-19 pandemic (April 2020 to February 2021), using the same methodology for both periods. We recruited participants by random-digit-dialing and collected data by self-administered web-based questionnaires. Questionnaires documented socio-demographic characteristics and social contacts for two assigned days. A contact was defined as a two-way conversation at a distance [≤]2 meters or as a physical contact, irrespective of masking. We used weighted generalized linear models with a Poisson distribution and robust variance (taking possible overdispersion into account) to compare the mean number of social contacts over time by characteristics. Results: A total of 1291 and 5516 Quebecers completed the study before and during the pandemic, respectively. Contacts significantly decreased from a mean of 8 contacts/day prior to the pandemic to 3 contacts/day during the spring 2020 lockdown. Contacts remained lower than the pre-Covid period thereafter (lowest=3 contacts/day during the Christmas 2020/2021 holidays, highest=5 in September 2020). Contacts at work, during leisure activities/other locations, and at home with visitors showed the greatest decreases since the beginning of the pandemic. All sociodemographic subgroups showed significant decreases of contacts since the beginning of the pandemic. Conclusion: Physical distancing measures in Quebec significantly decreased social contacts, which most likely mitigated the spread of Covid-19.
Subject(s)
COVID-19ABSTRACT
IntroductionIn Canada, first and second doses of mRNA vaccines against SARS-CoV-2 were uniquely spaced 16 weeks apart, but the duration of single-dose protection remains uncertain. We estimated one- and two-dose mRNA vaccine effectiveness (VE) among healthcare workers (HCWs) in Quebec, Canada including protection against varying outcome severity, variants of concern (VOC), and the stability of single-dose protection out to 16 weeks post-vaccination. MethodsA test-negative design compared vaccination among SARS-CoV-2 test-positive and weekly-matched (10:1), randomly-sampled, test-negative HCWs using linked surveillance and immunization databases. Vaccine status was defined by one dose [≥]14 days or two doses [≥]7 days before illness onset or specimen collection. Adjusted VE was estimated by conditional logistic regression. ResultsPrimary analysis included 5,316 cases and 53,160 controls. Single-dose VE was 70% (95%CI: 68-73) against SARS-CoV-2 infection, 73% (95%CI: 71-75) against COVID-19 illness and 97% (95%CI: 92-99) against associated hospitalization. Two-dose VE was 86% (95%CI: 81-90) and 93% (95%CI: 89-95), respectively, with no associated hospitalizations. VE was higher for non-VOC than VOC (73% Alpha) among single-dose (77%, 95%CI: 73-81 versus 63%, 95%CI: 57-67) but not two-dose recipients (87%, 95%CI: 57-96 versus 94%, 95%CI: 89-96). Across 16 weeks, no decline in single-dose VE was observed with appropriate stratification based upon prioritized vaccination determined by higher versus lower likelihood of direct patient contact. ConclusionOne mRNA vaccine dose provided substantial and sustained protection to HCWs extending at least four months post-vaccination. In circumstances of vaccine shortage, delaying the second dose may be a pertinent public health strategy to consider.
Subject(s)
COVID-19ABSTRACT
Background To eliminate cervical cancer as a public health problem, the World Health Organization currently recommends routine vaccination of adolescent girls with two doses of the human papillomavirus (HPV) vaccine before sexual initiation. However, many countries have yet to implement HPV vaccination because of financial or logistical barriers to delivering two doses outside the infant immunisation programme. Methods Using three independent HPV transmission models, we estimated the long-term health benefits and cost-effectiveness of one-dose versus two-dose HPV vaccination, in 188 countries, assuming that one dose of the vaccine gives either a shorter duration of full protection (20 or 30 years) or lifelong protection but lower vaccine efficacy (e.g., 80%) compared to two doses. We simulated routine vaccination with the 9-valent HPV vaccine in 10-year-old girls at 80% coverage for the years 2021–2120, with a one-year catch-up campaign of 11–14-year-old girls at 80% coverage in the first year of the programme. Results Over the years 2021–2120, one-dose vaccination at 80% coverage was projected to avert 112.9 million (range of medians: 75.8–176.2) and 148.0 million (111.6–187.6) cervical cancer cases assuming one dose of the vaccine confers 20 and 30 years of protection, respectively. Should one dose of the vaccine provide lifelong protection at 80% vaccine efficacy, 155.2 million (143.7–170.3) cervical cancer cases could be prevented. Around 65 to 889 additional girls would need to be vaccinated with the second dose to prevent one cervical cancer case, depending on the epidemiological profiles of the country. Across all income groups, the threshold cost for the second dose was low: from 0.85 (0.07–3.82) USD in low-income countries to 18.08 (−3.62–85.64) USD in high-income countries, assuming one-dose confers 30-year protection. Conclusions Results: were consistent across the three independent models and suggest that one-dose vaccination has similar health benefits to a two-dose programme while simplifying vaccine delivery, reducing costs, and alleviating vaccine supply constraints. The second dose may be cost-effective if there is a shorter duration of protection from one dose, cheaper vaccine and vaccination delivery strategies, and high burden of cervical cancer.
Subject(s)
Neoplasms , Papillomavirus Infections , Uterine Cervical NeoplasmsABSTRACT
Background: The Canadian epidemics of COVID-19 exhibit distinct early trajectories, with Quebec bearing a very high initial burden. The semaine de relache, or March break, took place two weeks earlier in Quebec as compared to the rest of Canada. This event may have played a role in the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We aimed to examine the role of case importation in the early transmission dynamics of SARS-CoV-2 in Quebec. Methods: Using detailed surveillance data, we developed and calibrated a deterministic SEIR-type compartmental model of SARS-CoV-2 transmission. We explored the impact of altering the number of imported cases on hospitalizations. Specifically, we investigated scenarios without case importation after March break, and as scenarios where cases were imported with the same frequency/timing as neighboring Ontario. Results: A total of 1,544 and 1,150 returning travelers were laboratory-confirmed in Quebec and Ontario, respectively (with symptoms onset before 2020-03-25). The cumulative number of hospitalizations could have been reduced by 55% (95% credible interval [95%CrI]: 51-59%) had no cases been imported after Quebec's March break. However, had Quebec experienced Ontario's number of imported cases, cumulative hospitalizations would have only been reduced by 12% (95%CrI: 8-16%). Interpretation: Our results suggest that case importation played an important role in the early spread of COVID-19 in Quebec. Yet, heavy importation of SARS-CoV-2 in early March could be insufficient to resolve interprovincial heterogeneities in cumulative hospitalizations. The importance of other factors -public health preparedness, responses, and capacity- should be investigated.