A clinic selling separate measles, mumps and rubella vaccines has been told to remove "misleading" claims from its website implying a link between the MMR jab and autism.
Complaints were made about the Cheshire-based Children's Immunisation Centre during the measles outbreak centred on Swansea.
The Advertising Standards Authority (ASA) decided the clinic's language "could have caused fear and distress".
The centre said it had now complied.
One person died and a total of 1,219 suspected measles cases were diagnosed during the Swansea area measles epidemic, which was officially declared over in July.
As part of the response from public health officials, almost 76,000 unscheduled MMR vaccinations were given to people around Wales who had not been immunised in a bid to bring the epidemic under control.
The Children's Immunisation Centre offered single vaccines to parents, running a clinic in Swansea and others in England.
In its response to the ASA, the centre said it offered a safe alternative for parents who needed to have their children protected from childhood diseases but did not wish to undergo government or NHS programmes such as the MMR vaccine.
It also argued its website information did not constitute advertising.
But the ASA said because the centre "promoted non-government recommended vaccination and because the overall context of the website focused on their claim that a single MMR vaccination was linked with autism, we considered the language used could have caused fear and distress without justifiable reason and we concluded the website was irresponsible".
Three complainants, including a GP, challenged whether the centre's 100% safety claim could be substantiated, while two said the advert was irresponsible and could cause fear and distress because it appeared during the measles outbreak in south Wales.
The ASA ruled that the website breached regulations because it advertised prescription-only medicines.
The centre told the ASA each of its 20,000 patients had a record card and not one had been hospitalised or had regression, autism or other health issues after vaccination.
But the ASA noted that a sample complaint log supplied by the centre confirmed some children had developed minor and major complications as a result of receiving a vaccination ranging from a rash and high temperature to emergency hospital admission.
The ASA said: "Because Children's Immunisation Centre did not have a 100% safety record, we concluded the claim was misleading."
It added: "We considered the website had probably been live for some time before the outbreak of measles in Wales, during April and May 2013.
"However, we noted two links referenced the Welsh measles outbreak."
The ASA said it had not seen robust evidence that linked a single MMR vaccine with autism, concluding that that website was misleading.
It ruled: "The ad must not appear again in its current form.
"We told Children's Immunisation Centre not to promote prescription-only medicines and to remove claims not supported by objective scientific evidence."
Dr Andrew Wakefield's research linking the MMR jab to autism was published in 1998 has since been entirely discredited.
In a statement to BBC Wales, Zoe Miller from the Children's Immunisation Centre said: "We're now fully ASA compliant, everything that was requested has been taken off the website."