The town’s outbreak control board was created in June 2020 in a bid to reduce the impact of coronavirus in local communities.
Members of the board - which is made up of a number of representatives from Barnsley Council, Public Health England, South Yorkshire Police and education leaders - are urging residents to remain wary.
At the start of August, the infection rate for 65 to 69 year olds was 154.8 but most recent figures show rates have risen to 309.5 - a 99.9 per cent increase.
Elsewhere, the rate for 55 to 59 year olds has more than doubled from 151.2 on July 1 to 364.1 per 100,000 residents - a 140 per cent increase.
A statement on behalf of the board’s members said: “We’ve returned to a climb in all-age case rates, and as our baseline number was quite high to start with, it puts Barnsley above the England average.
“Like other areas of the country, this is down to the ongoing conditions for community transmission a more relaxed approach to social mixing and safety measures now largely voluntary.
“However, we know that the most common variant, Delta, is also highly transmissible and while having both doses of the vaccine makes you far less likely to become seriously ill from Covid, it’s still a pretty unpleasant experience.”
Residents are also being encouraged to take lateral flow tests - which provide results within 30 minutes without the need to go to a lab - twice a week to ensure the spread is handled.
“We need to live safely with Covid and make sure that we continue to do everything we can to support those in our communities who still feel vulnerable,” the board added.
“Small actions add up to make a really big difference to the risk.
“That this has been a long and difficult time, but please continue to do everything you can.”
More than 84 per cent of eligible Barnsley residents have now had their first dose of the vaccine, and almost 80 per cent have had their second, but recent cases have spiked in older age groups.
Julia Burrows, director of public health in the town, said: “As well as providing us with some protection from becoming infected, the vaccine can also prevent severe illness and death if we do still become infected.
“On average the vaccines being used in the UK are between 91 and 97 per cent effective in preventing hospital admission.
“It also reduces the risk of new variants mutating and emerging, and so speeds each of us and all of us towards full recovery from the pandemic.”