With COVID-19 deaths and hospitalizations dropping, more Americans are gathering. But before you plan your next party, think twice about holding it indoors. A new study confirms what scientists have been warning all along  — small, indoor events are more likely to spread COVID-19 than larger, outdoor venues even if people are vaccinated. And even for outdoor events, three mitigation measures can reduce transmission even further.

The report just released from The University of Texas at Austin was developed in partnership with the public health officials in Austin, Texas. Researchers put together two hypothetical case studies, a business conference with 3,000 attendees and an outdoor festival with 50,000 people in attendance. According to Axios, they found that the outdoor festival, even though it was much larger, had a lower per-person impact on total infections over the following four weeks of the study.

Dr. Joe Gastaldo, an infectious disease expert from Ohio Health, said outdoor gatherings are always less risky than their indoor counterparts. But being in close quarters with other people even at an outdoor concert, baseball game or other event still gives the virus opportunities to spread.

“If you are outdoors on top of each other, to the point where you could actually smell someone smoking a cigarette or perhaps someone’s body odor, that’s really too close,” he said. “If you are outdoors and you can’t physically distance and people are next to each other in a public situation, you should be wearing a mask regardless of your vaccination status.”

The researchers also found that pre-event testing requirement were more effective than vaccine mandates in preventing people with infections showing up at the events. Three key factors were determined to reduce the risk of transmission of COVID-19 in large events:

• The structure of the event. The first consideration is the size, duration, density, and the venue itself. By limiting the number of people who attend the event, spacing them appropriately, and choosing outdoor or very well-ventilated places to host the event, you can mitigate transmission risk significantly.

• The state of COVID-19 in the community. “If the local healthcare system is strained, the additional spillover infections from the event into the community could be catastrophic,” wrote the researchers.

• The risk reduction measures. Event organizers should plan to reduce the risk of infection by requiring proof of vaccination, a negative COVID-19 test prior to entry to the event, and wearing facemasks.

The bottom line, says Axios, is that outdoor events are still a lot safer than those held indoors.