Is there substantial evidence that masks or lockdowns slow the spread of COVID-19?

There are dozens of scientific studies showing that wearing masks and instituting lockdowns or stay-at-home orders have been effective in slowing the spread of the virus that causes COVID-19.A review of face mask studies in the Proceedings of the National Academy of Sciences journal found that the "literature offers evidence in favor of widespread mask use as source control to reduce community transmission."A study in the Applied Health Economics and Health Policy journal found that lockdown policies "have been able to reduce the number of COVID-19 cases in the countries that implemented them."A year into the pandemic, evidence has accumulated showing how face masks work in slowing the transmission of COVID-19. The Centers for Disease Control and Prevention discusses on its website the effectiveness of cloth masks.