Population-based seroprevalence survey: post-pandemic COVID-19 vaccination, related factors, and geographic distribution of vaccine acceptability in Chile.

BACKGROUND

Prevention of infectious diseases is based on host protection, especially using vaccines. Several factors have been linked to the acceptance of vaccines in the population. Chile achieved high COVID-19 vaccination coverage early in the pandemic. The study aimed to determine the prevalence of antigens and antibodies, vaccination status, geographical distribution, and factors related to vaccine acceptability.

METHODS

In two Chilean cities, the fourth round of a population-based seroprevalence cross-sectional survey was conducted in May 2024. 654 participants aged seven or older were recruited. After signing consent, participants were interviewed, blood samples were taken to identify antibodies against SARS-CoV-2 using ELISA, and antigens were assessed through a nasal swab rapid test. Territorial analysis of the vaccine dose distribution was carried out.

RESULTS

All participants tested negative for antigens and positive for antibodies against SARS-CoV-2, with an overall vaccination uptake rate of 98,5%. However, their vaccination status was heterogeneous. Territorial distribution showed a slight geographical clustering of vaccine doses in both cities. 52.7% had the basic scheme and/or boosters, 32.1% had the bivalent vaccine, and 13.7% had anti-Omicron. Self-report identification with a risk group was not associated with vaccine adherence. City, age, education, and comorbidities were associated with perceived and actual risk discrepancies.

CONCLUSIONS

Overall, vaccine acceptance is high. However, the acceptance of the last two doses was below expectations and showed heterogeneous geographical distribution. Adulthood is the most important predictor of vaccine uptake. Participants underestimated their level of risk. Risk communication must be improved, especially for risk groups, to help them perceive themselves as beneficiaries of vaccination. Efforts should be made to disseminate information on vaccine safety and counter misinformation to increase knowledge about vaccines.