Luke Philben was playing happily on the floor when his mother, Sam Jackson, looked across and saw something was not right. Six-month-old Luke had a strange smile on his face, was holding his arm out at an angle and his body was twitching.

Terrified, Jackson began carrying Luke to the car to drive him to hospital, but by the time she reached the driveway he was having such violent fits he was frothing at the mouth. She called paramedics, who arrived just as Luke was turning blue. ''I was screaming. I thought he was dead. It was really, very traumatic,'' she says.

At the hospital, doctors checked Luke over and sent him home. They told Jackson seizures related to fever were common in young children and Luke's high temperature may have been due to his routine immunisations the day before.

Pupils at Scotch College lining up for Salk vaccine injections in 1956.

But 10 days later, Luke had another seizure and was admitted to hospital, where he had a third seizure that was so severe he had to be resuscitated. Brain scans came back clear, and Luke was prescribed drugs for epilepsy.

But the seizures kept coming in the months afterwards. Jackson and her partner, Tom Philben, were convinced Luke's immunisations were to blame.

As it turned out they were wrong. But the fears that repeatedly drove Jackson to the internet to scour the sites of anti-vaccination groups add them to the growing number of parents around Australia whose trust in the power of vaccination to keep their children safe is declining.

Ava Donovan (far left), 9, and her friend Luke Philben, 7, have a form of epilepsy called Dravet syndrome, which would have revealed itself with or without vaccination. Photo: Wayne Taylor

A new Australian survey confirms that many parents have serious concerns about the safety of vaccines given to children. Doctors worry that if these fears are not addressed they may change behaviour, causing parents to delay or withhold vaccines and risk their children being struck by diseases such as measles and whooping cough.

In the past, parents have vaccinated their children after seeing the damage such diseases can cause. But as epidemics become fewer, there are heightened fears about the possible side effects of vaccines. Indeed, doctors are concerned we may be seeing an emerging crisis of confidence in the benefits of childhood vaccination.

Associate Professor Julie Leask, of the National Centre for Immunisation Research and Surveillance, based at the University of Sydney, was an adviser on>the survey - the first to measure attitudes to vaccination in Australia.

Commissioned to coincide with the release of a television documentary, Jabbed, on vaccinations, the survey canvassed the views of 1300 Australians, including 400 parents. While childhood vaccination rates for two-year-olds remain high at 92 per cent, the survey found that 53 per cent of parents had general concerns about vaccinating their children. (Of these, 45 per cent vaccinated anyway, while 8 per cent either delayed or withheld vaccines.)

Vaccines are medicines that prevent people from acquiring serious infectious diseases. They work by stimulating the immune system to produce antibodies to fight a particular infection, helping it to quickly detect and destroy the infection when it becomes a threat.

Leask was surprised the survey showed that one in four parents was worried about a particular aspect of vaccination. Chief among those worries were concerns about an increasing number of vaccines and inadequate safety testing.

''It taps into this idea of the infant as being young and vulnerable and needing our protection, and vaccines being these mysterious things that go into a healthy baby to protect them against diseases we may not have ever seen,'' she says.

Parents also worried that their child's immune system could be ''overloaded'', a fear that scientists are keen to dispel, pointing out that the immune system responds independently to each infection, so cannot be overloaded or damaged by giving children a range of vaccines. They say serious side effects from vaccines are extremely rare, and there is strict safety testing

Some fears about vaccines are misplaced and can cause widespread harm and anxiety. For example, measles epidemics continue to break out across Britain more that a decade after disgraced doctor Andrew Wakefield published a study in The Lancet claiming to show a link between the measles, mumps and rubella vaccine and autism.

Wakefield's research was later declared fraudulent and unethical and his theory was widely debunked, but cases of measles have since skyrocketed after vaccine rates plummeted. In 2006, a 13-year-old boy became the first person in more than a decade to die of the disease in Britain.

But damage can also be caused by what turn out to be problem vaccines, such as CSL's Fluvax, which was designed to protect against seasonal and swine flu. In 2010, it caused 410 adverse reactions in Australian children under five, including 67 who had febrile convulsions, before health authorities moved to ban it for that age group.

Writing in the Medical Journal of Australia last month, public health physician Paul Effler and epidemiologist Heath Kelly said global fears of a swine flu pandemic led to ''accelerated approval" of Fluvax despite a lack of robust evidence of its safety in children.

They say stricter protocols and improved surveillance are needed after vaccines are approved in order to maintain public trust ''and ensure the long-term success of paediatric influenza vaccination programs''.

For the past 15 years at the Royal Children's Hospital, many parents with doubts about vaccination have met with immunisation paediatrician Jenny Royle. Often they are stunned to hear that some childhood vaccines protected against diseases for which there is no cure, such as whooping cough. (Parents might live around the corner from a hospital and think that if their baby caught whooping cough, doctors would be able to fix it.)

''We give supportive treatment, so you give babies fluids in drips and you put them in intensive care and give them oxygen when they turn blue, but there is no specific treatment to cure whooping cough,'' Royle says. ''It's a horrendous infection and even in modern Melbourne we are terribly limited in the impact we can make.''

Australia is in the grip of a whooping cough epidemic, with 10,134 cases reported in children under 15 last year. Two infants died, both aged under eight weeks, when they were too young to be vaccinated.

As with whooping cough, doctors are restricted in what they can do when meningitis takes hold. There is a treatment, but it does not necessarily guarantee a good outcome.

''You can be rushed to hospital and an hour later they have in the fridge the exact antibiotic used to treat it, but you can already be deaf and brain injured,'' Royle says.

''Because the immune system is so underdeveloped against the meningitis bacteria at a young age, it gets in the body and multiplies and the treatment is not given in time because the disease doesn't declare itself early enough.''

Hesitant parents need their questions answered quickly, Royle says, because the worst thing that could happen is for their children to get a disease while they are still trying to work out whether to administer the vaccine that prevents it.

Royle says her first task with hesitant immunisers is to work out the source of their anxiety. Had they heard about a worrying side effect? If so she provides information about how commonly it occurred with a particular vaccine. She points out that all medicines, even aspirin, have side effects.

''I'm not here hiding things from people. I'm very open about the range of side effects and how often they occur. I guess by talking about them you can then weigh up the chance of them happening, and how significant that would be, versus the chance of getting the disease and how significant that would be. It helps you in your risk/benefit discussions with people.''

Each year, the National Centre for Immunisation Research and Surveillance compiles a report of all adverse events reported in Australia following immunisation, but not necessarily caused by it. In 2011, the most current year for which data is available, there were 1121 such events in children under seven, including 531 in which there was a reaction at the injection site and 301 cases of fever.

More seriously, there were 44 cases of convulsions and 38 hypotonic-hyporesponsive episodes in which babies can become floppy and unresponsive. The episodes are frightening for parents but babies usually recover quickly with no long-term consequences.

Between 2002 and 2011 nine deaths following vaccination in children under seven were reported to Australia's drug regulator, the Therapeutic Goods Administration. After investigation, links to vaccination were ruled out in seven cases. In two cases, authorities were unable to confirm or exclude any contribution by the vaccine. In Queensland, a two-year-old girl died in her cot the day after having a Fluvax shot in 2010, and a coroner was unable to determine the cause of her death.

Before licensing a new vaccine for use in Australia, the TGA requires manufacturers to provide detailed data supporting its safety and effectiveness. The TGA continues to monitor vaccines for safety once they are approved, with all adverse events entered into a database and analysed regularly by medical officers in an effort to detect any problems.

Some side effects are expected with particular vaccines - for example, up to three out of 100 children can develop diarrhoea or vomiting in the week after receiving the vaccine against rotavirus, a severe form of gastroenteritis. TGA officers are looking for anything unexpected, such as in the case of Fluvax, which was triggering febrile convulsions in one in 100 children - 10 times the expected rate.

In 2011-12 more than 800,000 children were fully immunised in Australia and authorities say it is vital to consider adverse events in the context of thousands of diseases being prevented, some of them potentially fatal.

Fears about vaccines can stem from information overload, rather than ignorance. Research in the US and Britain has found that the more educated parents are, the more likely they are to oppose vaccination. Leask says this group is more inclined to question medical intervention in general.

''As part of their practice of trying to be 'good parents', they will feel it's important to research what they do with regard to their children's health … they might not just go ahead with immunisation without a lot of questioning. If their friends are not vaccinating they may see it as more normal to question it and select out vaccines, maybe even demand a special schedule for their child,'' she says.

The Australian survey of attitudes showed the internet was the main source of information for 50 per cent of people who oppose vaccination, while supporters overwhelmingly obtain information from a family doctor. Online searches would inevitably turn up anti-vaccination websites, Leask says, but do not create doubt where none had previously existed.

''It's an attempt to rationalise an emerging position you have on vaccination by going online and finding things that suit your theory and cherry-picking them,'' she says.

''People who are against vaccination will go and look for things that support that view, and they'll find them online much more than with conventional health professionals.''

For Luke Philben's family, however, the opposite was true. As Sam Jackson scoured the internet in her search for an explanation, she came across an article by a woman whose son had Dravet syndrome - a rare and severe form of epilepsy. It was, she said, ''like looking in the mirror''. A gene test confirmed the diagnosis.

Soon after, Jackson became aware of the work of Melbourne neurologist Ingrid Scheffer, who had studied cases of children who developed severe seizures soon after vaccination. Out of 14 such cases, Professor Scheffer found that 11 patients had gene mutations that cause Dravet syndrome, which usually emerges around six months of age and is associated with intellectual disability.

That meant many of the children with suspected vaccine reactions were destined to develop the devastating disorder anyway. At most the vaccine caused a fever that triggered the first seizure, just as a cold or toothache might. Luke has a friend, Ava Donovan, 9, who also has Dravet syndrome. Her first seizure occurred after a virus when she was five months old - not after her shots.

Leask says despite a perception that anti-vaccination groups are fuelling doubts about vaccines through the internet, there are bigger forces at play. Often there is an assumption that if such groups did not exist, no one would have any concerns. But wider changes in society are having an influence, including reduced exposure to the diseases that vaccines protect against.

A shift from the days of doctor knows best towards a model of care in which patients make informed decisions about their treatment is also part of the picture, along with the rise of alternative therapies. ''All of these broader changes may be influencing shifts in support for vaccination,'' Leask says.

Jackson spent six months blaming immunisation for Luke's seizures, and herself for taking him to have his shots. Now she knows his first seizure would have emerged with or without the vaccine. She has chosen not to immunise him further because the jabs are a trigger for him to have a seizure, just like jumping on a trampoline or going outside on a hot day. But Luke's family relies on other parents immunising their children, because a fever from a disease like measles could threaten his life.

Vaccines are given to the vast majority of children, and diseases can emerge at certain ages. Leask says that by chance alone, children can develop a disease or syndrome of unknown origin soon after having their shots. ''People want to know what's causing it and they blame the vaccine,'' she says.

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What causes GBS?

Many things can cause GBS; about two-thirds of people who develop GBS symptoms do so several days or weeks after they have been sick with diarrhea or a respiratory illness. Infection with the bacterium Campylobacter jejuni is one of the most common risk factors for GBS. People also can develop GBS after having the flu or other infections (such as cytomegalovirus and Epstein Barr virus). On very rare occasions, they may develop GBS in the days or weeks after getting a vaccination.