More than 1,000 people - mainly children - have queued up for MMR vaccinations in the wake of the measles epidemic.
The number of confirmed cases of measles in the Swansea epidemic remains at 588, according to Public Health Wales.
Special vaccination clinics were held on Saturday, with an NHS spokeswoman reporting parents beginning to queue up an hour before they were due to start, leading to them opening earlier to cope with the demand.
All four drop-in clinics, at Morriston, Singleton, Neath Port Talbot and the Princess of Wales hospitals, were "extremely busy" all day, she said.
Up to 20 new cases of the potentially deadly virus are being reported by GPs per day, with 109 new ones in a week over the Easter period. Health officials said on Friday that an estimated 3,800 children in the Swansea area had still not had the MMR vaccine, and urged parents to act.
Sara Hayes, Abertawe Bro Morgannwg University Health Board public health director, said: "We are absolutely delighted with the response from parents.
"We were hoping for 800 vaccinations across all four sites, but the actual figure is estimated to be around 50% higher, at 1,100 - 1,200. We'll know the final total later.
"We've vaccinated a wide range of age groups, mainly children, but also some of their parents, and other adults.
"This is a very helpful step in tackling this measles outbreak, and safeguarding our population for the future."
The drop-in MMR vaccination clinics will also be held next Saturday at all four hospital sites and an immunisation campaign is due to be held in schools when they return from the Easter break.