Public health chief Jim McManus is advising residents to be 'cautious' after the lifting of national COVID restrictions - as figures show a significant increase of cases in Hertfordshire.
On Monday Prime Minster Boris Johnson signalled a lifting of most COVID restrictions from July 19, including the legal requirement to wear a face covering or to socially distance.
In the wake of the announcement, Mr McManus has pointed to data showing a 69.4 per cent increase in cases in the county in the seven days to Saturday, July 10 - as well as increasing levels of hospitalisation.
He also pointed to the one-in-three people across Herts and West Essex who have yet to receive their first dose of the vaccine.
Mr McManus said: "There is no good time to exit restrictions - and whenever we do, we will have an exit wave.
"The issue will be down to how much we, as residents, organisations and employers, decide to stay safe. And if the caution I am seeing continues, then this third wave will be less harmful than other waves."
Nevertheless, estimates suggest there could be up to 100,000 cases of COVID recorded per day, which could lead to up to 10,000 new cases of 'long COVID' per day.
"That alone should make us want to protect others, particularly younger people, and do our bit," Mr McManus added.
Across Herts, the data shows infection rates are increasing most rapidly among 17 to 18-year-olds, with rates also rising 'quite quickly' in the 19 to 24 and 25 to 39 age groups.
Despite the lifting of measures, there will still be travel controls and a duty to self-isolate if contacted by Test and Trace, as well as strong guidance on wearing face coverings in closed places such as public transport.
Mr McManus said "There are still an awful lot of people not fully vaccinated - and the virus can reach them", and stressed that the virus is still out there and "won't end when the rules change".
He added: "I will continue wearing a face covering in every shop, to protect the staff in the shop and to show respect and courtesy."
Businesses will also still have a duty to keep their employees and customers safe, which will be rooted in health and safety guidance and regulations.
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