Experts fear a below-average uptake of jabs could leave areas more vulnerable to fast-spreading variants.
Over three-quarters of all adults in the UK and more than two-thirds in Northamptonshire have received at least one dose.
Yet that figure drops to 60.7 per cent in Northampton and 59.5 percent in Corby.
Vaccinations are now on offer for anyone over 25 and people are being offered second doses after eight weeks instead of 12 in an effort to speed up the rollout and combat rising cases of the Delta strain which is threatening to delay the final stage of easing restrictions on June 21.
Chris Pallot, director of Northamptonshire’s Covid-19 vaccination programme, said: "It's very fair to say that uptake rates for many of the age cohorts have been slightly lower than we would be comfortable with in Corby and Northampton.
"We know the population is slightly younger so they're always going to get called later.
"But I would like to see more of our 40-year-olds come forward and there are 5,000 slots each week available for them to do so."
We revealed last month that Lakeside surgery, one of the biggest in Corby, had opted out of delivering vaccines to under-40s.
Surgery bosses said: "We do not believe it would be in the best interests of all of our patients, particularly those with chronic conditions whose ongoing care has perhaps been impacted the most over the last 12 months."
A new vaccination facility is due to open in Rockingham Road later on June 21 to add more capacity for the town.
Five of the county's former boroughs and districts — Kettering, Wellingborough, Daventry, South and East Northamptonshire — are either above the national figure or just below on both first and second doses.
But Northampton again trails with 41.8 percent of the target delivered and Corby even lower on 38.5 percent.
The number of new positive Covid-19 tests across Northamptonshire has climbed by nearly 40 percent in the last week.
A variant, now dubbed Delta, led to a rise in hospital cases among those who had not been vaccinated in hardest hit areas.
Work is also going on with community leaders in a bid to increase awareness of the vaccination programme.
Mr Pallot added: "We know particular communities are much more reluctant than others to come forward, we've seen that principally from our eastern European communities.
"We are doing a lot of work with community leaders and people who can hopefully influence those members of our community to accept the offer of a vaccine because this really is the way to protect yourselves and our families and our loved ones.
“Uptake of the vaccine has been extremely positive in our county.
"More than 760,000 doses have been administered and 77 percent of the 30-and-over population have received a first dose of the vaccine.
“Getting vaccinated is the single most important thing we can do to protect ourselves, our loved ones and our communities against coronavirus.
"We’re determined no one is left behind so I would urge everyone who’s eligible to come forward for their vaccine as soon as they are invited.
"The offer of a vaccine doesn’t expire so if you’ve previously received an invitation for your first dose but haven’t yet booked your appointment, now is the time to do so.
"And when the time comes for your second dose, please remember to keep your appointment because you need both doses to ensure you are fully protected from coronavirus."