Figures from NHS England have revealed that in Portsmouth 24,048 boosters and third doses were given to people in that age group by November 28 - or 78.7 per cent of the cohort.
This is below the average for England of 80.7 and and below the rate in the Hampshire County Council area of 85.6 per cent.
Helen Atkinson, public health director for the city, said this was partly due to ‘higher levels of deprivation compared to other areas within Hampshire’.
She said: ‘We are working hard to reach all vulnerable groups in Portsmouth to urge them to get their vaccines as soon as they are eligible.
‘We are pleased to see that nearly four out of five over 65s have had their booster but as we head into Christmas it is vital that everyone who can get one does so.
‘The Covid-19 booster vaccine dose helps improve the protection gained from the first two doses of the vaccine for those people who have had both their first and second doses and helps give longer-term protection against getting seriously ill from Covid-19.
‘We know that immunity gained from having the vaccine, or from having coronavirus, reduces over time, and as we are now facing a new variant that we know spreads more readily, those eligible should book their booster as soon as they can.’
It comes as a mobile booster bus, run by the Hampshire and Isle of Wight Clinical Commissioning Group, successfully delivered 250 booster jabs in Portsmouth on Friday.
Ms Atkinson added: ‘It proved very popular, so along with our partners in the NHS, we're keen to get the mobile pop-up bus to as many city locations as possible to help reach those who may have difficulty in travelling to the vaccination locations.
‘The dates and times will be shared on the council’s social media channels as soon as we know where and when.’
The NHS data also showed 75.8 per cent of care home residents aged 65 and over in Portsmouth had a booster or third dose by November 28.
This is above the England average of 72.5 per cent. In Hampshire the rate was 76.0 per cent.
Roger Batterbury, chairman of Healthwatch Portsmouth, had concerns about how vulnerable adults could access the jabs.
‘Healthwatch Portsmouth will be asking questions of our local health teams about uptake of the booster vaccine offer made to those vulnerable adults in their own homes who need a home visit and the care home coverage to ascertain what the plans are locally to ensure everyone who is eligible gets their Booster,’ he said.
‘We do need clear guidance on this and ease of access to a Booster ‘when and where convenient for patients’ especially those aged over 65.
‘Healthwatch Portsmouth is aware from the most recent research on Covid it strongly suggests that a booster vaccination is effective against the variants that are around at the moment. The advice is if eligible and offered the opportunity, you should get your Covid booster jab as soon as you can.’
Boosters are set to be offered to everyone aged 18 and over by the end of January.
Third doses, separate to boosters, will only be offered to people with specific immunity issues.