Background By July 14, 2021, 81•3 % of adults (aged ≥18 years) in Chile had received a first SARS-CoV-2 vaccine and 72•3% had received a second SARS-CoV-2 vaccine, with the majority of people given Sinovac's inactivated CoronaVac vaccine (75•3% of vaccines dispensed) or Pfizer-BioNTech's mRNA BNT162b2 vaccine (20•9% of vaccines dispensed). Due to the absence of simultaneous real-world data for these vaccines, we aimed to compare SARS-CoV-2 IgG positivity between vaccines using a dynamic national monitoring strategy. Methods From March 12, 2021, 28 testing stations for SARS-CoV-2 IgG detection were installed in hotspots based on cellular-phone mobility tracking within the most populated cities in Chile. Individuals voluntarily approaching the testing stations were invited to do a lateral flow test by finger prick and respond to a questionnaire on sociodemographic characteristics, vaccination status (including type of vaccine if one was received), variables associated with SARS-CoV-2 exposure, and comorbidities. We compared the proportion of individuals testing positive for anti-SARS-CoV-2 IgG across sites by week since vaccination between recipients of CoronaVac and BNT162b2. Unvaccinated participants served as a control population and were matched to vaccinated individuals on the basis of date of presentation to the testing station, gender, and age group. Individuals were excluded from the analysis if they were younger than 18 years, had no declared gender, had an invalid IgG test result, had previously tested positive for SARS-CoV-2 infection on PCR, could not recall their vaccination status, or had been immunised against COVID-19 with vaccines other than CoronaVac or BNT162b2. Here, we report data collected up to July 2, 2021. Findings Of 64 813 individuals enrolled, 56 261 were included in the final analysis, of whom 33 533 (59•6%) had received at least one dose of the CoronaVac vaccine, 8947 (15•9%) had received at least one dose of the BNT162b2 vaccine, and 13 781 (24•5%) had not received a vaccine. SARS-CoV-2 IgG positivity during week 4 after the first dose of CoronaVac was 28•1% (95% CI 25•0-31•2; 220 of 783 individuals), reaching a peak of 77•4% (75•5-79•3; 1473 of 1902 individuals) during week 3 after the second dose. SARS-CoV-2 IgG positivity during week 4 after the first dose of the BNT162b2 vaccine was 79•4% (75•7-83•1; 367 of 462 individuals), increasing to 96•5% (94•9-98•1; 497 of 515 individuals) during week 3 after the second dose and remaining above 92% until the end of the study. For unvaccinated individuals, IgG seropositivity ranged from 6•0% (4•4-7•6; 49 of 810 individuals) to 18•7% (12•5-24•9; 28 of 150 individuals) during the 5 month period. Regression analyses showed that IgG seropositivity was significantly lower in men than women and in people with diabetes or chronic diseases for CoronaVac vaccine recipients (p<0•0001), and for individuals aged 60 years and older compared with people aged 18-39 years for both vaccines (p<0•0001), 3-16 weeks after the second dose.Interpretation IgG sero...

During the COVID-19 crisis, the Chilean Ministry of Health and the Ministry of Sciences, Technology, Knowledge and Innovation partnered with the Instituto Sistemas Complejos de Ingeniería (ISCI) and the telecommunications company ENTEL, to develop innovative methodologies and tools that placed operations research (OR) and analytics at the forefront of the battle against the pandemic. These innovations have been used in key decision aspects that helped shape a comprehensive strategy against the virus, including tools that (1) provided data on the actual effects of lockdowns in different municipalities and over time; (2) helped allocate limited intensive care unit (ICU) capacity; (3) significantly increased the testing capacity and provided on-the-ground strategies for active screening of asymptomatic cases; and (4) implemented a nationwide serology surveillance program that significantly influenced Chile’s decisions regarding vaccine booster doses and that also provided information of global relevance. Significant challenges during the execution of the project included the coordination of large teams of engineers, data scientists, and healthcare professionals in the field; the effective communication of information to the population; and the handling and use of sensitive data. The initiatives generated significant press coverage and, by providing scientific evidence supporting the decision making behind the Chilean strategy to address the pandemic, they helped provide transparency and objectivity to decision makers and the general population. According to highly conservative estimates, the number of lives saved by all the initiatives combined is close to 3,000, equivalent to more than 5% of the total death toll in Chile associated with the pandemic until January 2022. The saved resources associated with testing, ICU beds, and working days amount to more than 300 million USD. Funding: This work was supported by the ANID PIA/APOYO [Grant AFB180003 and AFB220003], used to hire research assistants for developing solutions, information systems, data management, and training of field staff. Fieldwork was funded by the Ministry of Health of the Government of Chile. M. Goic acknowledges the financial support of Fondecyt [Project 1221711] and the Institute for Research in Market Imperfections and Public Policy [Grant IS130002 ANID]. D. Sauré acknowledges the financial support of Fondecyt [Project 1211407]. Finally, G. Weintraub and A. Carranza thank the Stanford RISE COVID-19 Crisis Response Faculty Seed Grant Program for helpful financial support.

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