SAN FRANCISCO, Calif. (KRON) – Concerts and outdoor events are returning, and many are requiring proof of vaccination as part of new safety protocols designed to help prevent the transmission of COVID-19. But while experts say being outdoors is less risky in general, they continue to recommend additional precautions for those visiting crowded outdoor venues.

Health experts say the delta variant is more contagious than the strain American was dealing with last winter, and even fully vaccinated people need to be careful in certain situations.

“If you’re stuck in a crowd with people all around you, particularly yelling and screaming like at a concert or football game, I think that’s a risky situation for you and I would try and avoid it right now,” Dr. John Swartzberg said.

U.C. Berkeley infectious disease expert Dr. John Swartzberg says those most at risk are people who are not yet vaccinated.

Dr. Aruna Subramanian, infectious disease professor at Stanford, agrees.

“If you are doing those activities where you’re close together and you’re shouting, and cheering and singing, then you are likely to aerosol [the virus] if you have COVID-19 and there is a risk to those around you,” Dr. Subramanian said.

In an effort to stem the spread, several concert organizers have adopted stricter rules for entry. Live Nation Entertainment and IMGoing have already stated they will allow performers to decide whether there should be vaccine requirements for their shows. Napa’s BottleRock music festival is requiring proof of vaccination or a negative COVID test. Concert promoter AEG also announced vaccination requirements for all of its concerts and festivals, which include Coachella and the New Orleans Jazz Festival, among others.

But as more and more events agree to vaccination requirements, there are still those that have yet to adopt the measures.

At Levi’s Stadium where the San Francisco 49ers will kick off their preseason schedule, for instance, proof of vaccination is not required, nor is a negative COVID test. Masks are also optional in the stadium’s outdoor spaces.

This is why health experts urge safety.

“We don’t know who is vaccinated and who is not, and unfortunately … with the new virus that’s going around, even if you’re vaccinated you can have a lot of viral particles in your nasal passages,” Dr. Subramanian said.

“I always carry a mask with me,” Dr. Swartzberg said. “If I’m going out with a walk with my wife, we always just have a mask in our pockets, because what if we run into six or seven people that we know and we don’t know if they’re vaccinated or not?”

Some scenarios, however, are at least considered less risky.

“You can be the only person in a Trader Joe’s and that will be relatively risk-free, versus being intimate with somebody outdoors who is unvaccinated,” UCSF Infectious Disease Specialist Dr. Peter Chin-Hong said.

It is suggested to use an N95 mask, or to double-mask, when around crowds of people at large gatherings.