RESUMO
Objective: To investigate a cluster epidemic of coronavirus disease 2019 (COVID-19) infections in a school in Longchuan County, Yunnan Province, and further guide the prevention and control of COVID-19 in the border area. Methods: According to the Protocol on Prevention and Control of Novel Coronavirus Pneumonia (8th Edition), an epidemiological investigation was performed on all COVID-19 cases to collect the information on demographics, onset, diagnosis and treatment, prognosis, and epidemiological history. Close contacts were also tracked to determine the transmission chains. Results: In this cluster epidemic, a total of 37 COVID-19 cases were identified, including 32 females and 5 males aged from 13 to 25 years, who were 35 students and 2 teachers. The student cases were found in four classes of two grades. Furthermore, gene sequencing showed that all cases had been infected with delta variants, belonging to the same transmission chain that was not related to the previous epidemics in Dehong Prefecture. In additionally, a total of 2 127 close contacts were found. After 21 days of centralized quarantine for medical observation, all close contacts tested negative for SARS-CoV-2. In the COVID-19 cases, only one case remained positive for SARS-CoV-2, while the other 36 cases were successfully treated and became negative. Conclusion: This school cluster is caused by the border villagers who contacted the water polluted with SARS-CoV-2. It warrants more strict management of students from border villages and their belongings to prevent similar epidemics in school settings.
RESUMO
BACKGROUND: In partial response to the coronavirus disease 2019 (COVID-19) pandemic, countries around the world are conducting large-scale vaccination campaigns. Real-world estimates of vaccine effectiveness (VE) against the B.1.617.2 (Delta) variant are still limited. An outbreak in Ruili city of Chinaprovided an opportunity to evaluate VE against the Delta variant of two types of COVID-19 vaccines in use in China and globally - inactivated (CoronaVac and BBIBP-CorV) and adenovirus type 5 vectored (Convidecia) vaccines. METHODS: We estimated VE using a retrospective cohort study two months after the Ruili vaccination campaign (median: 63 days). Close contacts of infected people (Chinese nationality, 18 years and above) were included to assess VE against symptomatic Covid-19, COVID-19 pneumonia, and severe COVID-19. We calculated the relative risks (RR) of the outcomes for unvaccinated compared with fully vaccinated individuals. We used logistic regression analyses to estimate adjusted VEs, controlling for gender and age group (18-59 years and 60 years and over).We compared unvaccinated and fully vaccinated individuals on duration of RT-PCR positivity and Ct value. FINDINGS: There were 686 close contacts eligible for VE estimates. Adjusted VE ofad5-vectored vaccine was 61.5% (95% CI, 9.5-83.6) against symptomatic COVID-19, 67.9% (95%CI: 1.7-89.9) against pneumonia, and 100% (95%CI: 36.6-100) against severe/critical illness. For the two inactivated vaccines, combined VE was 74.6% (95% CI, 36.0-90.0) against symptomatic COVID-19, 76.7% (95% CI: 19.3-93.3) against pneumonia, and 100% (95% CI: 47.6-100) against severe/critical COVID-19. There were no statistically significant differences in VE between twoinactivated vaccines for symptomatic COVID-19 and for pneumonia, nor were there statistically significant differences between inactivated and ad5-vectored VE in any of the three outcomes. The median durations of RT-PCR positivity were 17 days for fifteen people vaccinated with an inactivated vaccine, 18 days for forty-four people vaccinated with the Ad5 vectored vaccine, and 26 days for eleven unvaccinated individuals. INTERPRETATION: These results provide reassuring evidence that the three vaccines are effective at preventing Delta-variant COVID-19 in short term following vaccination campaign, and are most effective at preventing more serious illness. The findings of reduced duration of RT-PCR positivity and length of hospital stay associated with full vaccination suggests potential saving of health-care system resources.