A fourth COVID-19 surge is blanketing the U.S., and the delta variant is the culprit.

"Where did this delta variant come from? It came from unvaccinated people getting infected in large numbers allowing the virus to continue mutating," says Dr. Gregory Poland, an infectious diseases expert and head of Mayo Clinic's Vaccine Research Group.

In the past, a person with COVID-19 might infect two to four people. But with the delta variant, one person can infect nine people, according to Dr. Poland. He says if you want to protect yourself and your family, wear a mask, especially indoors, and get vaccinated with an appropriate series of one of the COVID-19 vaccines.

"These are the most studied vaccines in the history of the world," Dr. Poland emphasizes. "There have never been this many people who have received this many doses of vaccines during this amount of time with as much scrutiny as these COVID-19 vaccines have had."

In this Mayo Clinic Q&A podcast, Dr. Poland answers questions about a person's waning immunity and the likelihood of COVID-19 booster shots. He also explains the two phases of immunity and goes into detail about the extensive Federal Drug Administration license approval process for COVID-19 vaccines.

Research disclosures for Dr. Gregory Poland.