Objective To estimate the effectiveness of a two dose vaccine schedule (mRNA-1273, BNT162b2, and BBIBP-CorV) against SARS-CoV-2 infection and covid-19 related death and short term waning of immunity in children (3-11 years old) and adolescents (12-17 years old) during periods of delta and omicron variant predominance in Argentina. Design Test negative, case-control study. Setting Database of the National Surveillance System and the Nominalized Federal Vaccination Registry of Argentina. Participants 844 460 c hildren and adolescents without previous SARS-CoV-2 infection eligible to receive primary vaccination schedule who were tested for SARS-CoV-2 by polymerase chain reaction or rapid antigen test from September 2021 to April 2022. After matching with their corresponding controls, 139 321 (60.3%) of 231 181 cases remained for analysis. Exposures Two dose mRNA-1273, BNT162b2, and BBIBP-CorV vaccination schedule. Main outcome measures SARS-CoV-2 infection and covid-19 related death. Conditional logistic regression was used to estimate the odds of SARS-CoV-2 infection among two dose vaccinated and unvaccinated participants. Vaccine effectiveness was estimated as (1–odds ratio)×100%. Results Estimated vaccine effectiveness against SARS-CoV-2 infection was 61.2% (95% confidence interval 56.4% to 65.5%) in children and 66.8% (63.9% to 69.5%) in adolescents during the delta dominant period and 15.9% (13.2% to 18.6%) and 26.0% (23.2% to 28.8%), respectively, when omicron was dominant. Vaccine effectiveness declined over time, especially during the omicron period, from 37.6% (34.2% to 40.8%) at 15-30 days after vaccination to 2.0% (1.8% to 5.6%) after ≥60 days in children and from 55.8% (52.4% to 59.0%) to 12.4% (8.6% to 16.1%) in adolescents. Vaccine effectiveness against death related to SARS-CoV-2 infection during omicron predominance was 66.9% (6.4% to 89.8%) in children and 97.6% (81.0% to 99.7%) in adolescents. Conclusions Vaccine effectiveness in preventing mortality remained high in children and adolescents regardless of the circulating variant. Vaccine effectiveness in preventing SARS-CoV-2 infection in the short term after vaccination was lower during omicron predominance and decreasing sharply over time. Trial registration National Registry of Health Research IS003720.

BackgroundWith the emergence of the COVID-19 pandemic, increasing numbers of cases of the multisystem inflammatory syndrome in children (MIS-C) have been reported worldwide; however, it is unclear whether this syndrome has a differential pattern in children from Latin America and the Caribbean (LAC). We conducted a systematic review and meta-analysis to analyze the epidemiological, clinical, and outcome characteristics of patients with MIS-C in LAC countries.MethodsA systematic literature search was conducted in the main electronic databases and scientific meetings from March 1, 2020, to June 30, 2021. Available reports on epidemiological surveillance of countries in the region during the same period were analyzed.ResultsOf the 464 relevant studies identified, 23 were included with 592 patients with MIS-C from LAC. Mean age was 6.6 years (IQR, 6–7.4 years); 60% were male. The most common clinical manifestations were fever, rash, and conjunctival injection; 59% showed Kawasaki disease. Pool proportion of shock was 52%. A total of 47% of patients were admitted to the pediatric intensive care unit (PICU), 23% required mechanical ventilation, and 74% required vasoactive drugs. Intravenous gamma globulin alone was administered in 87% of patients, and in combination with steroids in 60% of cases. Length of hospital stay was 10 days (IQR, 9–10) and PICU stay 5.75 (IQR, 5–6). Overall case fatality ratio was 4% and for those hospitalized in the PICU it was 7%.ConclusionLimited information was available on the clinical outcomes. Improvements in the surveillance system are required to obtain a better epidemiologic overview in the region.

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Introduction. In Argentina, an estimated 400 000 varicella cases occur annually. Given the under-recording of existing cases, the actual burden of disease is unknown. Objective. To assess the burden of varicella before the introduction of the varicella vaccine in the national immunization schedule. Materials and methods. Retrospective, analytical, observational study carried out in three hospitals of Argentina. Review of medical records from outpatient visits to the Emergency Department and from patients younger than 18 years hospitalized for varicella. Period: 1/2011-12/2013. Results. A total of 382 782 outpatients were seen; 3367 (0.88 %) corresponded to visits due to varicella; 57.6 % were ≤ 4 years old. A total of 164 (4.9 %) patients required hospitalization, with an overall hospitalization rate of 65.3/10 000 hospitalized patients/year (95 % confidence interval [CI]: 55.4-76.5); hospitalization rate in healthy children: 57.2/10 000 (95 % CI: 67.7-48.0); median age: 31.5 months. The most common causes of hospitalization were skin and/or soft tissue infections (61.1 %) and respiratory infections (10.1 %). Also, 54.3 % were treated with acyclovir and 73.1 %, with antibiotics. Bacteremia developed in 5/67 patients (7.5 %), all cases were caused by Gram-positive cocci and occurred in immunocompetent patients. Out of 19 immunocompromised patients, 36.8 % had complications (5 skin and/or soft tissue infection and 2 pneumonia cases). The median length of stay was 4 days, which is significantly more prolonged in immunocompromised patients. One patient required intensive care. No patient died. Conclusion. The burden of disease was significant, with a considerable impact in patients without an underlying disease.

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