Residents of the Guatemalan town of Comitancillo suspect at least a dozen of the victims are their relatives, according to authorities in the Central American country.
Despite growing drug cartel violence in Mexico over the last decade, shootings and multiple killings are rare in the capital compared to other areas of the country.
Mexico will also work with other labs in Europe, China and Russia in vaccine development projects, although AstraZeneca is the only one that has guaranteed distribution across Latin America.