[Prevalence of SARS-CoV-2 antibodies in the State of Mato Grosso, Brazil: a population-based survey]

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

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.

Self-reported symptoms and seroprevalence against SARS-CoV-2 in the population of Mato Grosso: a household-based survey in 2020

OBJECTIVE:

This study aimed to analyze the association between self-reported symptoms and seroprevalence against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in the population of Mato Grosso.

METHODS:

A household-based survey was conducted on 4,206 adults from 10 municipalities of Mato Grosso, in the Brazilian Midwest, who were selected by cluster sampling in three stages. Questionnaires were applied between September and October 2020, and chemiluminescence was used for the quantitative determination of immunoglobulin G (IgG) antibodies against the S1 and S2 proteins of SARS-CoV-2.

RESULTS:

Approximately half (47.0%) of individuals with SARS-CoV-2 antibodies (12.5%) reported having no symptoms. The most prevalent symptoms among individuals with antibodies were body pain (37.0%), fever (32.9%), and smell and taste change (28.7%). The search for a basic health unit was predominant (45.0%) as the first service, and only 5.3% reported being hospitalized.

CONCLUSION:

A high proportion of asymptomatic cases of coronavirus disease 2019 (COVID-19) was identified in the general population, even among older adults and individuals with comorbidities.