A woman prepares to get her shot of the AstraZeneca vaccine for COVID-19 on the first day of a three-day vaccination campaign for people over age 35 in the Complexo da Mare favela of Rio de Janeiro, Brazil, Thursday, July 29, 2021. Some recipients will be monitored to study the rate of protection the vaccines provide and the extent to which virus variants are circulating. (Photo by Bruna Prado/AP Photo)
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