Parents have been forced to spend hours queuing outside vaccination centres in an effort to get their children polio boosters.
Health officials announced last month that all children aged between one and nine in London were to be offered a booster vaccine after the virus was detected in sewage samples.
All eligible children were to be offered a jab within four weeks, irrespective of whether they were behind on their vaccination schedule, to boost immunity, officials said on August 10.
But parents have reported difficulties trying to book appointments almost seven weeks after the campaign was launched.
Clare Bullock, from Forest Hill, south east London, was told by her GP they were not participating in the polio booster programme.
She later received a text message with a link to walk-in centres in her area, but there were no bookable slots for under-fives and “almost all” the appointments were scheduled during the working day.
Her partner was forced to take their two-year-old son to a walk-in centre on a Friday afternoon where they queued for two hours.
“It was meant to close at 5:30 and he got seen just before six, there were two people in the queue behind him and they were going to stop doing it after that and people were being turned away,” she said. “It was absolute chaos.”
Another parent in Bromley, south London, who did not want to be named, received a text message from her local NHS team advising she could book a booster for her six-year-old via a booking phone line.
But despite four attempts to call and make an appointment the line cut off each time following an automated message.
One mother in Lambeth also told The Telegraph she spent 35 minutes on the phone to the GP trying to book the booster for her children aged four and seven.
The only appointment she was able to secure was three weeks away and it will take 50 minutes to travel there.
Other parents have reported on social media that their GP practices are not offering the booster shots and they’ve struggled to secure appointments at pop-up clinics. It was expected GPs would do the majority of the boosters.
Health sources suggested there had been some pushback from already stretched family doctors over the programme.
The UK Health Security Agency said last month it had detected the polio virus 116 times in 19 sewage samples across London.
Some had been identified as the vaccine-derived poliovirus (VDPV2), which behaves more like the wild form of the disease and can cause paralysis.
The Joint Committee for Vaccinations and Immunisations recommended the supplementary booster campaign for children aged one to nine to help ensure there is a high level of protection from paralysis where the VDPV2 is circulating.
It was announced last week more than 40 sites across the capital are offering boost doses to five to nine-year-olds, while one to four-year-olds should continue to get their booster via their GP.
A spokesperson for the NHS in London said: “Children in London aged one to nine can get their booster or catch-up dose of the polio vaccine via a range of options, including GP practices and community pharmacies while 40 vaccination sites - available to all five to nine-year-olds - have been rapidly mobilised helping to accelerate the immunisation drive.
“The NHS has contacted all parents in London with children eligible and we encourage them to take up the offer as soon as possible.”