The impact of vaccination status on importation of COVID-19 among international travellers.

Governments worldwide are looking for ways to safely enable international travel while mitigating the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and the associated coronavirus disease 2019 (COVID-19). However, few data describe the impact of vaccination on importation of COVID-19. We took advantage of the sequential introduction of two government policies in Canada to evaluate the real-world evidence of vaccine effectiveness among 30,361 international travellers arriving by air in Alberta, Canada. The proportion of COVID-19-positive results for travellers who were either fully vaccinated or partially vaccinated was 0.02% (95% CI: 0.00-0.10) (i.e. one positive case among 5,817 travellers). In contrast, 1.42% (95% CI: 1.27-1.58) of unvaccinated travellers tested positive for SARS-CoV-2 (341 cases among 24,034 travellers). These findings suggest that COVID-19 vaccinations approved in Canada, substantially reduced the risk of travel-related importation of COVID-19 when combined with other public health measures. The low absolute rate of infection among fully vaccinated or partially vaccinated international travellers may inform quarantine requirements in this population.

Successful containment of a flight-imported COVID-19 outbreak through extensive contact tracing, systematic testing and mandatory quarantine: Lessons from Vietnam.

BACKGROUND: The importation of SARS-CoV-2 through air travel poses substantial risks to generate new COVID-19 outbreaks. Timely contact tracing is particularly crucial to limit onwards transmission in settings without established community transmission. METHODS: We conducted an in-depth analysis of the response to a big flight-associated COVID-19 outbreak in Vietnam in March 2020 that involved contact tracing, systematic testing and strict quarantine up to third generation contacts. RESULTS: 183 primary contacts from the flight as well as 1000 secondary and 311 third generation contacts were traced, tested, and quarantined across 15 provinces across Vietnam. The protracted confirmation of the index case at 3 days and 19 h after arrival resulted in isolation/quarantine delays of 6.8 days (IQR 6.3-6.8) and 5.8 days (IQR 5.8-7.0) for primary and secondary cases, respectively, which generated 84.0 and 26.4 person-days of community exposure from primary and secondary cases, respectively. Nevertheless, only 5 secondary cases occurred. CONCLUSIONS: A large flight-related COVID-19 cluster was successfully contained through timely, systematic and comprehensive public health responses despite delayed index case identification. Multiagency collaboration and pre-established mechanisms are crucial for low and middle income countries like Vietnam to limit community transmission after COVID-19 importation through air travel.

Effectiveness of interventions as part of the One Health approach to control coronavirus disease 2019 and stratified case features in Anhui Province, China: A real-world population-based cohort study.

BACKGROUND: Coronavirus-Disease-2019 (COVID-19) caused by Severe-Acute-Respiratory-Syndrome-Coronavirus-2 (SARS-CoV-2) is rapidly spreading worldwide causing a pandemic. To control the pandemic, the One Health approach (https://www.who.int/news-room/q-a-detail/one-health) is very important. We herein provide a real-world example of efficient COVID-19 control in Anhui Province, China with outbreak originating from imported cases through implementation of a series of measures as part of the One Health approach and describe the stratified cases features. METHODS: Since the identification of the first imported COVID-19 case on Jan 22, 2020, Anhui immediately initiated a sequence of systematic and forceful interventions. We detailed the control measures and analyzed the effects as demonstrated by the corresponding temporal changes of overall epidemiology data on confirmed, cured, and hospitalized cases and contacts. An accumulated number of 991 cases were confirmed, with a total number of 29,399 contacts traced. We further retrieved individual-level data of confirmed cases and compared them across stratifications by sex, age group, linkage to Wuhan, and period of diagnosis. RESULTS: With a series of interventions including active field investigation, case tracing, quarantine, centralization, education, closed management, and boundary control implemented, number of hospitalized COVID-19 cases peaked, new case disappeared, and all cases were discharged 21, 36, and 46 days after the identification of the initial case, respectively. Male patients were younger, more often had linkage to Wuhan, and received timelier care, but less often had infected cohabitants. Patients aged 25-44 years most often had linkage to Wuhan, while such frequency was lowest in those ≥65 years. Cases <25 years most often had a known contact with COVID-19 patients and any infected family member and cohabitant and were beforehand quarantined, and received fastest management. Patients with linkage to Wuhan were younger, less often had infected family member, had longer incubation period, and received earlier quarantine and timelier care. With more recent periods, the proportion of cases with linkage to Wuhan markedly decreased while the proportion of cases with known contact with COVID-19 cases dramatically increased; the proportions of patients with any infected family member or cohabitant, those beforehand quarantined, and those taking drugs before admission increased; incubation period lengthened, and patients received timelier professional care. Nonspecific systemic symptoms were most common, whose proportion decreased in more recent periods. CONCLUSIONS: Timely and powerful measures as part of the One Health approach (https://www.who.int/news-room/q-a-detail/one-health) effectively and efficiently controlled the COVID-19 outbreak in Anhui, which can be a good real-world example strongly demonstrating the usefulness of such measures in places with outbreaks originating from imported cases. Precise and dynamic prevention and control measures should be implemented and based on features including sex, age group, exposure history, and phase of outbreak.