I didn’t know you could get sick or die from them.”

The words were Charmaine Dunn-Myria’s, a 15-year-old schoolgirl in the same year at the Blue Coat Church of England school in Coventry as Natalie Morton, who died on Monday just hours after receiving the cervical cancer vaccine.

The shock and panic spread far beyond Natalie’s classmates. Her death represented every parent’s nightmare and caused many families to reconsider giving their children the vaccine.

Within hours, health chiefs throughout the UK quarantined all stocks of the vaccine which had originated in the same mass-produced batch as that used on Natalie and her classmates. They said it was a “precautionary measure”, and urged parents to remain calm.

Meanwhile there were reports of other girls at the school becoming nauseous and dizzy, and some being sent home. NHS Coventry suspended its immunisation programme to brief nurses on how to handle the torrent of questions from anxious parents and pupils about the safety, or otherwise, of the human papillomavirus jab.

For more than 24 hours, an ominous question mark hung over the much-touted Cervarix vaccine, hailed as a breakthrough in the fight against a killer disease when it was rolled out across schools both north and south of the border last year.

The picture began to change with the release late on Tuesday of the results of the post-mortem examination into Natalie’s death. The coroner attributed Natalie’s death not to the vaccine but to a previously unknown “serious underlying medical condition”. At Thursday’s inquest, it emerged that the teenager had been killed by a malignant tumour in her chest, which had spread to her heart and lungs and was compromising the blood flow to her entire body.

“It was so severe that death could have arrived at any time,” said pathologist Alexander Kolar.

According to Natalie’s stepfather, she had been “poorly for some time” and investigations were under way at the time of her death to identify the mystery illness.

Even that news was not enough to allay the fears of many parents. “It’s difficult as a parent not to feel uneasy after incidents like this. It makes you think twice,” Caroline, 34, who has a seven-year-old daughter at school in Glasgow, told the Sunday Herald.

“I’m relieved it’s not a decision I’ll have to make for a few years. This particular incident has been resolved, obviously, and it’s extremely sad – my heart goes out to that girl’s parents. But it did draw attention to some of the other cases which haven’t been resolved, as well as some of the concerns experts have about its safety.”

So are there really grounds for “thinking twice” about the vaccine? It’s true that a number of “adverse” reactions have been associated with GlaxoSmithKline’s Cervarix, as well as the rival brand, Gardasil, which is used for immunisation programmes in the US and Europe.

However, many experts argue that this is to be expected.

The monitoring process for any new drug – after it is rolled out from clinical trials involving hundreds of subjects to a sample size of millions in the general population – encourages doctors and the public to report any adverse event which occurs around the time of vaccination, however unlikely a link may appear.

Drug safety experts scour these reports for patterns. Most of the side-effects turn out to coincidental. In the US, 30 deaths have been linked to Gardasil, but in July last year safety regulator the Food and Drug Administration (FDA) said post-mortems revealed that the deaths had been caused by “other” factors.

In the case of Cervarix, GSK acknowledges a range of potential side-effects, from the “very common” – including headaches, fatigue, muscle pain, and redness or swelling around the injection site – to “common” reactions such as nausea, vomiting, diarrhoea, itching, joint pain, fever, or rashes.

On rare occasions following vaccination, girls may also experience dizziness, a hardening, tingling, or numb sensation around the injection site, or develop a respiratory infection.

All these would be classed as “adverse reactions”, but nothing out of the ordinary – and the vast majority of girls who have so far received the vaccination, amounting to tens of thousands in Scotland, have reported no side effects at all. In total, the UK government has reported 4657 adverse reactions from more than 1.4m doses since immunisation began.

“Since the thalidomide case in the sixties, our system of checking medications, which include vaccines, has become very strict,” says Dr Andrew Buist, deputy chairman of British Medical Association GP committee in Scotland. “They have to go through various stages of trials, first in the laboratory and then on animals, and then in healthy volunteers. So by the time a drug comes to market it’s been on trial for approaching 10 years usually.

‘‘But of course it’s the size of a trial in real-life which makes the difference – this vaccine alone will have been given to more than a million people. That’s obviously a very large cohort where you could start looking for very rare things that might happen, that don’t show up when you test it on a couple of thousand but might when you test it on hundreds of thousands.”

A handful of highly controversial cases have suggested that paralysis and brain damage are among Cervarix’s rarest side-effects.

Last December, 12-year-old Ashleigh Cave, from Merseyside, collapsed after receiving the Cervarix vaccine and was later admitted to hospital, apparently paralysed from the waist down. Guillain-Barre syndrome was suspected, a rare condition caused where the body’s immune system attacks its own peripheral nerve network – affecting the head, trunk and limbs, but not the brain or spinal cord.

Normally triggered following acute infections, such as influenza, it was first associated with flu vaccines during an outbreak in the US in the 1970s.

However, doctors later dismissed any link to Cervarix and the drug safety watchdog, the Medicines and Healthcare Products Regulatory Agency, pointed out that the condition occurs naturally in the population, at a rate of around 1500 cases per year. There was “no clear evidence” to link Ashleigh’s condition to the vaccine.

Nonetheless, the vaccines now look set to become the subject of legal scrutiny, as medical negligence cases gather steam on either side

of the Atlantic.

While the cumulative effect of these tragic incidents – all occurring around the time of a vaccination – is to give apparent credence to claims of vaccine dangers, it amounts to little more than circumstantial evidence at present. However, the scientific evidence of how vaccines have transformed public health and banished once prevalent and deadly diseases, such as smallpox and tuberculosis, remains overwhelming.

Part of the problem, according to Dr Buist, is that we find it difficult to weigh up risk.

“One of the problems of assessing risk is the sources that the general public will get their perception of risk from, and one of the big places is in the media,” he says. “For example, despite being an incredibly safe mode of transport, the aeroplane is perceived as quite risky compared to the car because every air crash is reported on the news; every car crash isn’t, because it’s so commonplace it’s not interesting. The media will want stories that sell newspapers and make good television.”

Indeed, a number of medical experts lambasted the press last week for “scaremongering” and “hysteria” following Natalie Morton’s death.

The fact is, the risk of a woman developing cervical cancer in her lifetime is around 1 in 136, whereas the risk of a “severe, life-threatening” reaction – such as anaphylactic shock – is around one in a million.

The vaccine, while not eliminating the need for smear tests, does protect against the two strains of HPV virus which cause more than 70% of cervical cancers.

But the debate around vaccines is more than just a numbers game. For every medic accusing the media of hype, there is a conspiracy theorist claiming whitewash and collusion in an “establishment” cover-up.

The new swine flu vaccines, due to be rolled out to vulnerable groups across the globe in the next couple of months, are the latest target of suspicion.

On Friday, Australia’s former federal health minister, Dr Michael Wooldridge, blasted those encouraging citizens to boycott the vaccine as “crackpots”.

“We are of course dealing with the first pandemic of the internet age, which poses its own problems,’’ he added.

Blogs and social networking sites are awash with rumours that the vaccines will cause everything from neurological disorders to reduced fertility and cancer – and even that the virus doesn’t actually exist, but was “invented” to be a moneyspinner for the pharmaceutical industry.

“Being a parent is a minefield of decision-making,” says Jackie, a 41-year-old mother of two daughters, aged 10 and 11, from Paisley.

“I think you have to keep and open mind, but also try to stay clear about the risks.

“Until there is overwhelming evidence to the contrary, I would still have my girls vaccinated.”