Steve Brown, director of Public Health Devon, said the current “gradual climb” to about 2.2% of people infected was also “likely to be higher than reported” because fewer people were testing.
He said: “We’re not back to the community infection rates we were seeing in the spring but we are seeing more cases in the community, which translates to increased cases in care homes and workplaces.”
Cornwall Council said, external its warning had been made as “thousands of people prepare to make the trip down to the county for holidays and festivals”.
Currently 2.7% of the population in Cornwall are thought to have the virus.
Rachel Wigglesworth, director of Public Health for Cornwall and the Isles of Scilly, said Covid was “very much still here and is once again spreading quickly through our communities”.
She said people were not being asked to put their lives on hold again, but to “remember to take those basic [hygiene, isolation and ventilation] precautions that we know work against Covid, and perhaps most importantly of all, make sure you’re up to date with the vaccinations”.