Festival-goers have reported testing positive for Covid-19 after heading to Latitude.
The Henham Park festival, attended by 40,000 people, went ahead at full capacity between July 22 and 25 as part of the latest phase of the government's event research programme.
Attendees needed a negative lateral flow test or proof they'd been double-jabbed.
But despite precautions, some have since reported positive PCR tests since the festival wrapped up on Sunday.
The organisers have been approached for comment.
A spokesman for the Department for Media, Culture and Sport said it was too soon to say what impact the festival would have on local case numbers.
"The findings are still being looked at and researched, and will be published in due course", he said.
Waveney MP Peter Aldous, who lives near Henham Park, said he had heard from a concerned constituent that Covid-19 protocols weren't being adhered to at the event.
He said: "The constituent told me that while they were at Latitude they did not think proper safety protocols were being followed. I have took note of those concerns and passed them onto government.
"As a resident of the local area, I think it's fair to say there was some apprehension about a spike in cases. But it's a balancing act.
"There was certainly a desire to get back to normal, and people were incredibly enthusiastic about it."
Suffolk County Council spokeswoman said no official "outbreak" had been declared at the county-level.
Thérèse Coffey, MP for Suffolk Coastal, said: "Due to the strength of the vaccine programme, it's great we're in a position where Latitude was able to go ahead.
"I'm glad it did, not least because organisers pushed up vaccine uptake by offering jabs to festival goers on-site.
"I don't predict a local spike which can be attributed to Latitude, as most festival goers stay on site."
One Latitude attendee, who did not want to be named, said fellow revellers she knew had tested positive since Sunday.
She said: "It was easy to think Covid no longer existed once you were in that bubble.
"I felt safe because I knew people needed lateral flow tests and two shots of the jab, but upon entry the organisers really weren't that strict about it.
"Everything was completely back to normal, like a pre-pandemic festival would be. It's the most fun I've had in over a year."
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