The Prime Minister's claimed that Office for National Statistics data show 'clearly that infection levels are falling' yet the number of new coronavirus cases in the county reported daily has risen sharply during the last three days.
Mr Johnson also said hospital admissions had stabilised and scientists believed 'it is likely that the Omicron wave has now peaked nationally.'
Figures for Northamptonshire announced on Wednesday (January 19) showed more than 1,600 positive tests in the latest 24-hour period compared to 968 announced on Sunday (January 16).
Daily cases had dropped to under 1,000 from a peak of 2,267 on January 5.
And NHS England revealed Northampton General Hospital was officially full with no beds free for new patients on at least one day in the week between January 10 and 16.
And the county's Director of Public Health admitted the impact of children returning to school after Christmas and reductions in isolation periods were still uncertain.
Lucy Wightman said: "I am cautiously optimistic, but Northamptonshire doesn't always behave in the same way as other areas so we have case rates and outbreaks that are different.
"We have a very responsible community but I would urge everybody not to be complacent.
"We have have seen Northamptonshire's case rates rise after they had been seen to be coming down and we don't be caught out because we do not have a finite resource of hospital beds and staff."
Changes announced by the PM on Wednesday were:
■ Work From Home guidance dropped immediately
■ Covid passports no longer required from next Thursday
■ Face masks in school classrooms dropped today and in communal areas from next Thursday
■ Face masks in wider community including shops and on public transport also dropped from next Thursday
Northamptonshire's two main hospitals were treating 154 Covid patients by Wednesday, occupying more than ten percent of total beds.
According to NHS England, 27 people have sadly died while being treated for the virus in Northampton General Hospital since January 1 and another 18 in Kettering General Hospital — including five deaths confirmed on Thursday (January 20).
The hospitals' CEO, Simon Weldon, admitted: "We are fortunate that numbers have not risen in the way we initially expected.
"But that's still more than ten percent of our total bed stock given over to patients who have one condition and that is no healthy place for a system to be."
"I'm grateful for the fact that we're not where we thought we would be. But there are still considerable problems we are dealing with on a day-to-day basis."