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.

Objective: This study aimed to compare the prevalence of serum hepatitis B virus (HBV) markers in Inner Mongolia between 2006 and 2020.Methods: The same sampling process was used in investigations conducted in 2006 and 2020. A multi-stage stratified random sampling method was used to select subjects aged 1–60 years old from 12 cities in Inner Mongolia. Blood samples were collected to detect serological HBV markers including hepatitis B surface antigen (HBsAg), hepatitis B surface antibody (HBsAb), and hepatitis B core antibody (HBcAb). The prevalence of serum biomarkers of hepatitis B, standardized by age and sex, was analyzed and compared between 2006 and 2020.Results: There were 6,304 subjects in 2006 and 6,500 in 2020. The prevalence of HBsAg was higher in 2006 than in 2020 (standardized 4.11% vs. 2.75%, p < 0.001). The results were observed for the serum biomarkers of HBsAb (standardized 41.40% vs. 42.14%, p = 0.39) between 2006 and 2020, as well as HBcAb (standardized 22.91% vs. 20.15%, p < 0.001). The hepatitis B vaccine (Hep B vaccine) provides protection against HBV infection. In 2006, the proportions of timely birth dose (TBD) and 3-dose Hep B vaccine coverage for individuals aged 1–14 years were 80.57 and 89.35%, respectively. By 2020, these proportions increased to 97.43 and 96.97%, respectively.Conclusion: The prevalence of HBsAg decreased significantly from 2006 to 2020 in Inner Mongolia, suggesting that the Hep B vaccine has made remarkable progress in safeguarding the population against hepatitis B infection.

Infant hepatitis B vaccine coverage in China is high, with over 95% of infants immunized; however, high vaccine coverage can often mask low timeliness. The vaccination interval between the second and third dose is not clearly defined by immunization guidelines in China. This retrospective cohort study assessed the time interval distribution of hepatitis B vaccination among a cohort of randomly selected live births from Centers for Disease Control and Prevention across four provinces or municipalities in China between January 2017 and December 2021. Among the infants analyzed, 163,224 received the first dose of hepatitis B vaccine with 146,905 (90.0%) and 135,757 (83.2%) infants receiving the second and third doses, respectively. A total of 132,577 (90.2%) infants received the second dose between 28–61 days after the first dose. Of the 119,437 (88.0%) infants that completed the hepatitis B series between 61–214 days after the second dose, 87,067 (64.1%) infants were vaccinated with the third dose between 151–180 days after the second dose. The time interval distribution for the three doses of hepatitis B vaccine varied across the four provinces or municipalities (P<0.001). Of the 58,077 infants who completed the hepatitis B vaccine series, 36,377 (62.6%) infants used the same type of hepatitis B vaccine for all three doses. Overall, the timeliness of hepatitis B vaccination for infants was lower than expected, with regional disparities observed. This highlights the need for improved timeliness through the introduction of a defined timeframe for the last two doses of vaccine, and training for obstetricians and related personnel.