Effectiveness of CoronaVac in children 3 to 5 years during the omicron SARS-CoV-2 outbreak (preprint)

The outbreak of the B.1.1.529 lineage of SARS-CoV-2 (omicron) has caused an unprecedented number of Covid-19 cases, including pediatric hospital admissions. Policymakers urgently need evidence of vaccine effectiveness in children to balance the costs and benefits of vaccination campaigns, but the evidence is sparse or non-existing. Leveraging a population-based cohort of 490,694 children aged 3–5 years, we estimated the effectiveness of administering a two-dose schedule, 28 days apart, of CoronaVac using inverse probability-weighted survival regression models to estimate hazard ratios of complete immunization over non-vaccination, accounting for time-varying vaccination exposure and relevant confounders. The study was conducted between December 6, 2021, and February 26, 2022, during the omicron outbreak in Chile. The estimated vaccine effectiveness was 38.2% (95%CI, 36.5–39.9) against Covid-19, 64.6% (95%CI, 49.6–75.2) against hospitalization, and 69.0% (95%CI, 18.6–88.2) to prevent intensive care unit admission. The effectiveness was modest; however, protection against severe disease remained high.

Validation of a Methodology for the Detection of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) in Saliva by Real-Time RT-PCR (preprint)

Background: In January 2021, the city of Concepción in Chile suffered a second wave of COVID-19, while in early April 2021, all of Chile was facing the same situation. This generated the need to modify and validate a methodology for detecting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in saliva, thereby expanding the capacity and versatility of testing.Methods: People who came to the health center in Concepción city to perform a test of real-time reverse transcription polymerase chain reaction (RT-PCR) from a nasopharyngeal swab (NPS) specimen were invited to participate in this study. A total of 131 participants agreed to sign an informed consent and provide saliva and NPS specimens to validate a methodology in terms of sensitivity, specificity, and statistical analysis of the Ct values from RT-PCR.Findings: Calculations pertaining to the 127 participants who were ultimately included in the analysis were the following: sensitivity at 94·34% (95% CI: 84·34%-98·82%) and specificity at 98·65% (95% CI: 92·70%-99·97%). The saliva specimen showed a very similar performance to NPS as demonstrated with the diagnostic parameters.Interpretations: This RT-PCR methodology from the saliva specimen is a highly sensitive and specific alternative as compared to the reference methodology, which uses an NPS specimen. This modified and validated methodology is intended for use in the in vitro diagnosis of SARS-CoV-2, which provides health authorities in Chile and local laboratories with a real alternative for RT-PCR from NPS.Funding Information: Health Public Institute of Chile.Declaration of Interests: All authors declare no competing interests.Ethics Approval Statement: The study had the authorization of the Scientific Ethics Committee of the Health Service of Concepción, Chile Number 20-01-02. Parents or legal guardians for volunteers under the age of 18 signed the informed consent.