(NEXSTAR) — As we learn more about the omicron variant, it appears to have some significant differences from delta and other coronavirus variants that came before. One big difference is the kinds of symptoms that show up, especially in vaccinated people. Another difference, early research shows, is the virus’ incubation period.

An incubation period is the amount of time between when you’re exposed to a virus and when symptoms start to show.

A small study by the Centers for Disease Control found that omicron’s incubation appears to be about a day shorter than delta’s. With delta, the incubation time was typically about four days; with omicron, the period shortened to three days.

The incubation of the original COVID-19 variant was thought to be even longer, at about five days.

Why does the virus’ incubation period matter? It’s one factor that can contribute to how quickly it spreads. A short incubation period means someone can go from being exposed to the virus to transmitting it to others very quickly.

“With Omicron, most transmission occurs during the one to two days before onset of symptoms, and in the two to three days afterwards,” writes Harvard Medical School in a Q&A about omicron. “Wearing masks, particularly indoors, can help reduce the risk that someone who is infected but not yet experiencing symptoms may unknowingly infect others.”

People who test positive or are experiencing omicron symptoms should also stay home, isolate from others, and get tested for the virus.