We now know that the cervical cancer jab did not directly cause the death of Natalie Morton.  But parents will still worry, writes Sarah Boseley. 

Natalie Morton, the 14-year-old from Coventry who died in hospital after having the cervical cancer vaccination, was not killed by the jab.  Public health doctors breathed again when the preliminary result of her post-mortem was released on Tuesday night.  She had a serious underlying medical problem - nobody has yet specified what.  Yet she may well have died because she had the jab.  Though it may hot have been the cause, the HPV vaccine could have been the trigger.   

Vaccines are miraculous, life-saving inventions.  They have stopped our babies dying of diphtheria and being disabled by polio.  But they can kill.  It's extremely rare, but it happens. 

Let's be clear.  Nobody has died from the cervical cancer HPV vaccine, but one death in the UK and 32 in the US have been linked to it - meaning that these young women died of something within seven days of receiving the jab.  As with Natalie, it is highly unlikely the jab was the direct cause of death, and some of these deaths will have been totally coincidental. 

Paul Hunt, consultant in paediatric infectious diseases at St George's hospital, London, says there are three categories of side-effects with vaccines: local, such as pain and redness at the injection site; general, such as fever; and severe allergic reactions.  "These occur and are rare," he says.  "Maybe one in 1m doses will result in a severe anaphylaxis - the serious allergic reaction some people have to a bee sting and the antidote is usually adrenalin, which vaccinations should have in case." 

But beyond all that there is sometimes, as with Natalie, the existence of an unknown medical problem, which could have struck them down at any time.  "It's conceivable that a child would have an underlying problem with their heart or a heart valve or an unrelated seizure disorder, such as epilepsy, which has not until that event become evident.  The event could coincide with the vaccination," he says.  It is also possible that the vaccine - or the pain or anxiety around having the injection - could trigger the fatal episode. 

Public health officials who launch immunisation programmes for an entire population are aware of these risks.  But simple maths enables them to sleep at night.  Vaccines do good for vast numbers of people.  They save lives.  In the UK, more than 1.4m doses of the HPV vaccine were given and 4,657 adverse reactions, mostly of the sore arm variety, were reported to the Medicines and Healthcare products Regulatory Authority between April 2008 and September 2009.  The death of one girl from something triggered by the vaccine - if that is what happened - is a tragedy.  But set against the potential of the HPV jab to prevent maybe 400 of the nearly 1,000 deaths from cervical cancer each year, there is no contest in most medical minds.  "We are saving an awful lot more than one in a million lives," says Sean Kehoe of the Royal College of Obstetricians and Gynaecologists.  "We have to keep with the positive message that there is far more benefit than risk." 

"But what about the parents?  And here I have acknowledge a personal interest.  We are not so good at coolly considering the public health risk-benefit calculations.  We try to be rational, but can't help wondering if our daughter will be the next Natalie Morton. 

When the MMR (measles, mumps rubella) vaccine scare was triggered by a paper from Dr Andrew Wakefield and colleagues from the Royal Free hospital in London, who suggested a link to autism, my second daughter had not yet had the booster jab given at four years old.  Nervously, in spite of my own belief in what the public health experts were saying, I delayed it.  In the end, she had it during the catch-up campaign, was the only girl in the class to be called out for her jab, and fainted from anxiety. 

Now she is due to have the cervical cancer vaccine.  Her older sister has had the first two of three doses.  Last week, before Natalie died, I signed the permission form and sent it to school.  This time, I did not hesitate.  My 25-year-old niece was diagnosed with cervical cancer last year.  After surgery, she seems clear, but will need regular check-ups.  No cancer is anything other than horrible and we live in fear that it will return. 

The risk-benefit calculation I made, with my daughters, was easy.  but without cancer staring you in the face, it's harder, as many parents know.  "People are very bad at estimating their own risk of anything.  The fact that lots of people play the lottery shows that," says Dr Anne Szarewski of the Wolfson Institute of Preventive Medicine in London.  "People have a completely distorted idea of risk.  Sometimes they think it is much higher and sometimes they think it is much lower than it is." 

She has examined many women with abnormalities that could be the precursor to cervical cancer and has no doubt about the vaccine's value, but she acknowledges how much tougher it is to make the choice for someone you love rather than for yourself.  "Deciding for your daughter is a much more difficult decision," she says. 

Many parents will have been reassured by NHS Coventry's statement that Natalie died because of an unknown medical problem.  Many will find that scary too, just as some of us had moments of rising panic when we heard that children had died of swine flu only because of a health problem their parents had no clue about. 

One often undetected condition is an irregular heart rhythm.  Alison Cox, chief executive of Cardiac Risk in the Young, says it strikes without warning, can be triggered by fear or over-excitement and causes, in this country, about 12 deaths a week in under-35's.  "In 80% of kids, the first symptom is sudden death," she says.  She cites the example of an 18-year-old who died while cutting her birthday cake.  Not every underlying condition can be screened for, but this one - an irregular heart rhythm - can. 

There are no easy answers.  There is no test that can rule our every conceivable medical problem.  In the end, we all have to make a very personal decision, and what's worse is that we make it for our children and if anything happens to them, we will never forgive ourselves.  But there are risks whatever we decide.  My daughter could suffer some unexpected, incredibly rare reaction to the HPV vaccine, or she could in a few years, have unprotected sex and develop cervical cancer, which could kill her or destroy her chances of having a family.  I've made my choice and I'm sticking by it.

For more information on Cardiac Risk in the young visit c-r-y.org.uk