Objective To validate the telephone modality of the Latin American and Caribbean Food Security Scale (ELCSA) included in three waves of a phone survey to estimate the monthly household food insecurity (HFI) prevalence during the COVID-19 pandemic in Mexico. Design We examined the reliability and internal validity of the ELCSA scale in three repeated waves of a cross-sectional surveys with Rasch models. We estimated the monthly prevalence of food insecurity in the general population and in

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... olds with and without children, and compared them with a national 2018 survey. We tested concurrent validity by testing associations of HFI with socioeconomic status and anxiety. Setting ENCOVID-19 is a monthly telephone cross-sectional survey collecting information on the well-being of Mexican households during the pandemic lockdown. Surveys used probabilistic samples and we used data from April (n=833), May (n=850), and June 2020 (n=1,674). Participants Mexicans 18 years or older who had a mobile telephone. Results ELCSA had adequate model fit and HFI was associated, within each wave, with more poverty and anxiety. The COVID-19 lockdown was associated with an important reduction in food security; decreasing stepwise from 38.9% in 2018 to 24.9% in June 2020 in households with children. Conclusions Telephone surveys are a feasible strategy to monitor food insecurity with ELCSA.