CHICAGO (CBS) — In light of the Las Vegas mass shooting, organizers of the Chicago Marathon are reminding those running or planning to watch this Sunday that security measures are in place.

The biggest mass shooting in American history immediately prompted concern about Chicago’s largest spectator event — with an estimated 40,000 runners and walkers and 1 million spectators spread over 26.2 miles.

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Executive race director Carey Pinkowski says they’ve been working with local and federal law enforcement year-round, adding, “Security and safety of our participants are a primary focus of the event,” he said.

As in prior years, access to Grant Park will be limited starting the night before, and runners must use clear plastic bags for their gear.

“Remember, we started changing dramatically what we were doing after the Boston Marathon and we upped our game dramatically,” Mayor Rahm Emanuel said.

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Pinkowski said several elements have been put in place in response to what happened in Boston. “Our screening that takes place, our clear plastic bag, access to the park, access to the finish line, working with our volunteers with backpacks and bags…”

Still, Pinkowski says participants should use the same high level of vigilance they’ve become accustomed to.

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“You have to be aware of what goes on everyday, whether you’re attending a baseball game or you’re walking from the train or you’re commuting to work.”

That same mindset has been applied for the Cubs World Series, with playoffs at Wrigley Field starting Monday. And authorities point to extensive training — exactly a year ago, Cook County coordinated the biggest active shooter/terrorism drill in Illinois history.

However, as no scenario is going to be exactly like another, authorities have meetings planned this week with officials in Vegas to see what they can learn.

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A Chicago Police spokesperson stressed there is no known threat to the city.