Seroprevalence of Natural and Acquired Immunity against the SARS-CoV-2 Virus in a Population Cohort from Two Chilean Cities, 2020-2022

Viruses. 2023 Jan 10;15(1):201. doi: 10.3390/v15010201.


Background: Chile has achieved the highest coverage for vaccines against the SARS-CoV-2 virus worldwide.

Objective: To assess the progression of immunity (natural and acquired by vaccine) in a cohort from two Chilean cities.

Methods: Individuals (n = 386) who participated in three phases of population-based serial prevalence studies were included (2020-2021 and 2022). Presence of SARS-CoV-2 antibodies was measured in serum. Data including time of vaccination and type of vaccine received were analysed with descriptive statistics.

Results: Seroprevalence was 3.6% in the first round and increased to 96.9% in the second and 98.7% in the third. In the third round, 75% of individuals who had received the basal full scheme were seropositive at 180 days or more since their last dose; 98% of individuals who received one booster dose were seropositive at 180 days or more, and 100% participants who received two boosters were seropositive, regardless of time since their last dose. Participants receiving mRNA vaccines had higher seroprevalence rates over time.

Conclusions: The high vaccination coverage in Chile enabled the population to maintain high levels of antibodies. Vaccination boosters are essential to maintain immunity over time, which also depends on the type of vaccine administered.

Keywords: COVID-19; Chile; antibodies; immunity; seroepidemiology; seroprevalence; vaccines.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptive Immunity
  • Antibodies, Viral
  • COVID-19* / epidemiology
  • COVID-19* / prevention & control
  • Chile / epidemiology
  • Cities / epidemiology
  • Humans
  • SARS-CoV-2*
  • Seroepidemiologic Studies


  • Antibodies, Viral

Grants and funding

This research was funded by the Chilean National Research Agency, Grants code COVID-19-0589, FONIS SA21I0009 and FONDECYT 1201240. The research has been supported by WHO Unity Studies, a global sero-epidemiological standardization initiative, with funding to WHO by the COVID-19 Solidarity Response Fund and the German Federal Ministry of Health (BMG) COVID-19 Research and Development Fund.