Watchdogs were forced to fast-track investigation into the budget airline's commercials, which first aired on Boxing Day, after they received 2,370 complaints from furious viewers.
The adverts, which have now been dubbed "misleading", featured a picture of a large syringe and a vial labelled "vaccine", before text on-screen read: "vaccines are coming."
A narrator then said: "Covid vaccines are coming. So book your Easter and summer holidays today with Ryanair.
"One million seats on sale from £19.99 to sunshine destinations in Spain, Italy, Portugal, Greece and many more. So you could jab and go!"
The voiceover was accompanied with a series of images of people holidaying, as well as the block-capitals: "JAB & GO!"
Hundreds of complainants said the adverts were "irresponsible", while others said they claimed a large number of the UK population will be vaccinated against coronavirus by the summer holidays.
Currently, just over 10 million adults have been offered the first dose of the Covid-19 jabs. It has been predicted that the majority of adults in the UK will be offered the vaccine by mid-July should the NHS keep up the momentum of the vast programme - but this is by no means a guarantee.
Defending their advertising campaign, Ryanair bosses said the ads did not make any claims concerning who would be vaccinated, when they would be vaccinated, how vaccines were to be administered or how long it would take to achieve maximal protection once vaccinated. They added the "positive" and "uplifting" nature of the ads were hoped to encourage viewers to consider a "brighter future" - and pointed toward the UK Government's "optimistic" briefings ahead of the New Year.
But the Advertising Standards Authority (ASA) ruled that the ads breached rules regarding both "misleading" and "responsible" advertising.
"The specific references to Easter and summer holidays directly linked the rollout of the vaccine to the implication that many people who wished to go on holiday during those periods would be able to do so as a direct result of being vaccinated," a spokesperson explained.
"We considered that based on the information available at the time it was clear that it was highly unlikely that societal groups outside of phase one of the rollout would be maximally protected in time to holiday in either summer or Easter 2021.
"We therefore concluded that the implication in the ads that most people who wished to go on holiday at Easter or summer 2021 would be vaccinated in time to do so, and that being vaccinated against Covid-19 would allow people to go on holiday without restrictions during those periods, was misleading."
The ASA also raised concerns about the "jab and go" nature of the ads, which seemed to imply that individuals could obtain a vaccine "on demand".
"We further considered the ads encouraged people to behave irresponsibly by prompting those who were not yet eligible to be vaccinated to contact GPs or other NHS services in an attempt to arrange vaccination, at a time when health services were under particular strain," they added.
"For those reasons, we concluded the ad was irresponsible."
Ryanair, like most other airlines, have struggled with the travel restrictions put in place during the ongoing pandemic.
The company reported a £270 million quarterly loss, citing Covid-19 for 'wreaking havoc' on their finances.
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