More than 80% of Americans live in a county deemed to have "high" or "substantial" COVID-19 transmission. There's concern those numbers are going to increase as the U.S. heads toward the fall.

Health experts and officials have a simple message - getting a COVID-19 shot could be the difference between life and death.

"Delta virus is much more infectious. For those who are unvaccinated, it's more deadly and for those who are vaccinated, they're protected. So, we all need to be vaccinated," says Dr. Michael Saag, the associate dean of global health at the University of Alabama at Birmingham.

Just over 30% of those eligible to get vaccinated in the U.S. haven't done so and doctors say that's helping the delta variant spread.

"Vaccines protect you, but also vaccines protect other people around you. In a way, this is similar to not driving while intoxicated. We have an obligation to keep others safe in our society," says Dr. Leana Wen.

The rise in COVID-19 infections and hospitalizations has caused some businesses and school districts to change their mask guidelines. Health officials say masks help contain the spread, but the best tool against the pandemic is vaccination.

The Centers for Disease Control and Prevention reports the pace of vaccinations are rising, especially in some of the states that have the lowest rates.

MORE: Will COVID-19 vaccines work if you have a weak immune system? Here are some answers.