RESUMO
Phase 3 clinical trials and real-world effectiveness studies showed that China's two main inactivated COVID-19 vaccines are very effective against serious illness. In November 2021, an outbreak occurred in the Inner Mongolia Autonomous Region that provided an opportunity to assess the vaccine effectiveness (VE) of these inactivated vaccines against COVID-19 caused by the delta variant. We evaluated VE with a retrospective cohort study of close contacts of infected individuals, using a generalized linear model with binomial distribution and log-link function to estimate risk ratios (RR) and VE. A total of 8842 close contacts were studied. Compared with no vaccination and adjusted for age, presence of comorbidity, and time since last vaccination, full vaccination reduced symptomatic infection by 62%, pneumonia by 64% and severe COVID-19 by 90%; reductions associated with homologous booster doses were 83% for symptomatic infection, 92% for pneumonia and 100% for severe COVID-19. There was no significant decline in two-dose VE for any outcome for up to 325 days following the last dose. There were no differences by vaccine brand. Inactivated vaccines were effective against delta-variant illness, and were highly effective against pneumonia and severe COVID-19; VE was increased by booster doses.
RESUMO
The coronavirus disease 2019 (COVID-19) pandemic has had severe health impacts worldwide. We aim to provide suggestions to the government for managing serious infectious disease outbreaks in remote regions having relatively poor medical resources. Basic reproduction number (R0), incubation period, time from symptom onset to confirmation, and duration of hospitalization were analyzed. We compared the compositions of imported and local secondary cases and cases with mild/common and severe/critical illnesses according to age, sex, and clinical symptoms. From January 23 to February 19, 2020 (less than one month), 75 local COVID-19 cases were confirmed in Inner Mongolia. Among these, the median age was 45.0 years, and 33 (44.0%) were imported cases. More than 80.0% cases had mild/common illness. The case fatality rate was 1.3%, and R0 was estimated to be 2.3. The median incubation period was 8.5 days. There was a significant difference in the incubation period between imported and local secondary cases (P < 0.001). Early and mandatory control strategies implemented by the government were associated with a rapid reduction in COVID-19 incidence in Inner Mongolia.