Outbreaks of measles across England and Wales have reached the highest levels for 18 years, leaving young adults and teenagers whose parents did not get them immunised during the 1998 MMR scare most at risk, with many taken to hospital.

Public health campaigns are now being run across affected areas to persuade older people, teenagers, university students and young adults to get themselves vaccinated. All of these groups are not only vulnerable themselves but pose a risk to babies and toddlers.

The MMR vaccine scare – now proved to have been based on unfounded claims – led to many parents not letting their children be immunised against measles.

"People can think their teenager or young adult child is not at risk but that's not the case," said Dr Mary Ramsay, head of immunisation at the Health Protection Agency (HPA). "If you were not vaccinated at two and you're now 13, you're just as much at risk as when you were younger."

Toddlers who mixed with other children at nursery and pre-school groups before getting their vaccination at the recommended age of 13 months have also been badly affected, as have the children of Travellers.

"Measles is such an infectious disease that you only need one or two people who haven't had the vaccination to put at risk babies, toddlers and anyone else who is vulnerable, such as children with leukaemia who cannot have the vaccination and pregnant women who haven't been vaccinated," Ramsay added.

There were 2,016 confirmed cases of measles in England and Wales in 2012: the highest annual total since 1994. There were prolonged outbreaks in Sussex, where one in seven children have not been vaccinated, and in Merseyside. Heysham, Morecambe, Herefordshire and Gloucestershire.

Measles, Ramsey said is, an unpredictable disease. She said that Merseyside may have been affected because children go to a single A&E department at Alder Hey hospital. Sussex and Merseyside have been running campaigns since last summer to increase vaccination coverage. The outbreaks are now said to be under control.

Dr Tom Scanlon, director of public health for Brighton and Hove, said: "In years gone by, we had a lot of child deaths from measles. In the last outbreak in the city a few years ago, we had just under 50 children admitted to hospital with serious complications."

There have been 330 confirmed cases in Sussex since the start of 2012, including 195 cases in Brighton and Hove.

About one in every 15 children with measles will develop serious complications. The World Health Organisation recommends at least a 95% vaccination take-up to offer a community the best possible protection against a disease. About 82% of children in Brighton and Hove had received both doses of the MMR vaccine at the end of March 2012, an improvement on the 77% the year before.

Scanlon said: "There is a group of people in the city who don't believe in vaccination and a bigger group that doesn't believe in MMR. These beliefs might be based on things they have read or heard, but they are not based on science. So it may be that trying to convince them with science is never going to work.

"We in the public health community have to accept that some people just will never agree with vaccination, and even if – more likely when – their children catch measles, many of them will still try to justify their approach," Scanlon said. "Measles is a very contagious disease, it has the potential to be very unpleasant, sometimes serious and occasionally fatal."

Dr Ken Lamden, consultant in communicable disease control in Cumbria and Lancashire's health protection unit, said there have been 59 confirmed cases in Heysham and Morecambe since October 2012.

Across Greater Lancashire, he added, there had been more than 100 cases since the beginning of 2012. The majority are aged five to 16 years old, although adults up to the age of 30 have also been affected. About 25 of those cases were admitted to hospital. All have been discharged.

"It all dates back to the 1998 MMR scandal where take-up dropped by 10%," he said. "Once measles occurs in these groups, it's so infectious it can be passed to any group."

Cumbria and Lancashire NHS services are offering vaccinations in all primary and secondary schools. They are also writing to all parents of children aged five to 16 who did not have their children fully vaccinated at two to "ask them if they might like to reconsider", said Lamden. "We're doing our best but it's unpredictable how long the outbreak will take to get under control."