2:33 pm UTC May. 4, 2021 Show caption Hide caption Nurse Natasha Garcia prepares a lollipop and an "I Got My COVID-19 Vaccine" sticker for a recipient in a mobile clinic set up in the parking lot of a shopping center in Orange, Calif., April 29, 2021. Jae C. Hong, AP SAN FRANCISCO – It may not take true "herd immunity" to see a dramatic drop in COVID-19 cases. Some researchers say another 30 million to 40 million first shots could be enough for the United States to reach a vaccine tipping point and containment of the disease caused by the coronavirus. "It's just another 10% to 15% more people," said Dr. Eric Topol, a professor of molecular medicine at the Scripps Research Institute in La Jolla, California.