WASHINGTON, July 29 (Reuters) - The Smithsonian Institution reversed its mask policy on Thursday, requiring all visitors as young as age 2 to wear face coverings to enter its museums in an effort to thwart the fast-spreading Delta variant of the coronavirus. The Smithsonian, the world"s largest museum, education and research complex, with 19 museums largely concentrated in Washington, D.C., said it would reimpose the mask requirement beginning on Friday for vaccinated as well as unvaccinated patrons. Last month the Smithsonian said vaccinated people were exempt from wearing masks indoors. Patrons will be allowed to remove face coverings while eating or drinking in designated areas. The policy mirrors the U.S. Centers for Disease Control and Prevention"s newest recommendation that everyone wear masks indoors as COVID-19 rates spike across the nation, fueled by the more contagious Delta variant. The change comes at the height of the summer travel season, with tourists flooding into Washington, D.C., after a year of lockdowns that virtually shut down tourism. During the pandemic Smithsonian museums, which are free-of-charge, recorded only 3.3 million total visits in 2020, a fraction of the 22.1 million total visits in 2019, according to its website. Masks are a must to enter many of the top U.S. museums, including the American Museum of Natural History in New York, where until last week visitors could roll up their sleeves for a COVID-19 vaccination under the iconic blue whale. Shots now are being administered in another part of the Manhattan museum, which mandates "a facial covering throughout the visit for all visitors age 2 and up," according to the website. Mask policies regardless of vaccination status also have remained in place at the California Science Center in Los Angeles since its reopening in March from "an unprecedented 376-day closure of our facility" forced by the pandemic, a science center spokesperson said in an email. "To protect vulnerable community members, including our younger guests who are not yet eligible for COVID-19 vaccination, masks are required for everyone ages 2 and up," the spokesperson said.