vaccine A senior citizen receives a dose of Chinese-developed COVID-19 vaccine in Brasilia, Brazil, on March 22, 2021. Brazil is one of the countries hardest hit by the virus worldwide in terms of both deaths and cases, second only to the United States.Photograph by Lucio Tavora/Xinhua via Redux Please be respectful of copyright. Unauthorized use is prohibited. Brazil once vaccinated 10 million people for polio in a day. What went wrong with COVID-19? In a country known for past public health planning, coronavirus cases are still rising while immunizations lag—and now young people are getting hit the hardest. ByJill Langlois