Aug 2 (Reuters) - McDonald"s Corp (MCD.N) on Monday confirmed that all its customers and staff will need to start wearing masks again inside its U.S. restaurants in areas with high or substantial transmission, regardless of whether they are vaccinated or not. The resurgence of COVID-19 cases in the United States due to the Delta variant and the new guidance from the U.S. Centers for Disease Control and Prevention (CDC) that requires fully vaccinated individuals to wear masks have led companies to change their plans on vaccinations and masking. read more Last week, major companies including Alphabet Inc"s (GOOGL.O) Google, Uber Technologies Inc (UBER.N) and Facebook Inc (FB.O) said all their U.S. employees must get vaccinated to step into offices. read more McDonald"s also said that masks were always mandatory for staff and customers who were not vaccinated. The Associated Press first reported on the move.