I am compelled to respond to Ms B. Thorne's second letter to the Editor dated April 30.

First of all, I agree that referring to your letter as "hysterical" and "irresponsible" is not useful when discussing an issue as important as vaccinating our children against preventable and potentially fatal infectious diseases. Parents need to be informed in a calm manner about the tremendous safety record of vaccines and the risks of delaying or declining immunisations.

Concerns like yours are easily found on the Internet, and physicians need to be aware of them in order to prevent a loss of trust in the public health system.

The science of immunisations is very complex and even well-informed physicians may have difficulty keeping up with the changes and possible controversies. That is why physicians must rely on organisations such as the American Academy of Pediatrics (AAP), Centers for Disease Control and Prevention (CDC), the National Institutes of Health (NIH) and other expert panels to keep up-to-date. To expect the average parent to understand these complexities would be virtually impossible.

Unfortunately, there is an ever-increasing amount of unproven, scientifically invalid charges about alleged adverse effects of vaccines that proliferate on Web sites and via other media sources. Perhaps the most dangerous part of these stories is that the explanations are presented in a way that seem believable.

Issues of vaccine safety need to be balanced by presenting data regarding known benefits and risks of vaccines. Discussions that include theoretical risks, unfounded hypotheses, and unconfirmed data will only mislead and confuse the public.

Ms Thorne feels that "vaccinations can be dangerous". The overwhelming consensus from a public health standpoint is that children are far more likely to be harmed by these serious infectious diseases than by the immunisations. With the exception of smallpox, the viruses and bacteria that cause vaccine-preventable disease and death still exist. For example, measles causes nearly 1 million deaths in developing countries annually. Before the measles vaccine was developed in 1963, virtually every child in the US contracted measles (approaching the entire birth cohort of 3.5-4 million children). The death rate was one to two per 1,000 cases reported. Some developed encephalitis, often resulting in brain damage, at a rate of one in 800 to 1,000 cases.

During an epidemic of measles in the US in 1989-1991, more than 55,000 cases of measles were reported, with 150 measles-related deaths (a death rate of one in 500). If we stopped immunisation, measles would increase to pre-vaccine levels and an estimated 2.7 million deaths would be expected worldwide. (incidentally, where is the media and public outcry about these measles deaths? And people are worried about SARS?)

Immunisation has cut measles incidence by 99.9 percent. Measles has gone from being a "universal childhood disease" to one that is so rare that younger physicians have never seen a case (from a US public health position this triumph is surpassed only by eradication of polio in the US and Western Hemisphere and the worldwide eradication of smallpox). But the fact that it has not been eradicated in other parts of the world makes it an ongoing public health danger.

The 100 cases per year in the US are now primarily due to imported cases or exposure when travelling abroad. It does not really matter how many cases there have been in Bermuda unless you never travel and your children are never exposed to visitors and new residents coming from countries of lower immunisation rates.

In a district in Bavaria, Germany, more than 1,000 measles cases occurred between November 2001 and April 2002 because doctors were opposed to giving the measles vaccine (MMR). Venezuela has been affected by a measles epidemic since August, 2001, traced to one imported case from Europe; over the next seven months there were nearly 700 measles cases and one death, with those under age of five and young adults most affected.

There have been similar experiences in other countries like the Netherlands and Italy. Paediatricians and public health officials are extremely concerned about this potential "time bomb" if more children go unvaccinated. So far, Bermuda's children are protected by the concept of "herd immunity" because the majority of parents do choose to immunise their children.

Now compare the serious complications of natural measles infection with complications from the MMR vaccine (measles, mumps, and rubella). Vaccine-induced side effects are generally mild and self-limited and include fever in up to 15 percent and a rash in about five percent, usually seven to 12 days after the shot.

Febrile seizures can occur in one out of 3,000 doses, but these are usually in children with a prior history of seizures or who have a parent or sibling with a history of seizures. The risk of having a seizure due to a fever in the general paediatric population is two to three percent, which is much higher than occurs after the MMR vaccine.

Serious allergic reactions are very rare (less than one out of a million; the risk of a serious allergic reaction to peanut butter is much higher!).

The risk of a serious central nervous system effect is so rare that a causal relationship has not been proven. Encephalitis has been reported to occur at a frequency of less than one per million doses administered, which is actually lower than the observed incidence of encephalitis of unknown cause, thus the reported cases may simply be temporally, not causally related. This low frequency is 1,000 times lower than the incidence of encephalitis with a true measles infection.

Ms Thorne, if you feel that this "tiny percentage" of adverse events is unacceptable to you, then that is your choice. No physician can say that an immunisation (or any medicine or food we consume for that matter) is 100 percent risk-free. One must look at the balance of risks versus benefits to understand the importance of immunisations. I do not need to worry about the much higher risk of encephalitis or death if my children are exposed to measles one day.

As a paediatrician concerned about public health, however, I must care about more than my own children and patients.

To clarify and correct some of the points you make:

Hepatitis B is recommended as a universal vaccine to start in infancy because:

30-40 percent of people who acquire this disease have no risk factors

25-50 percent of children under the age of five who get hepatitis B will become chronic carriers, compared to six to ten percent of older children and adults

90 percent of infants born to a hepatitis B positive mother will become chronic carriers

Chronic hepatitis B can lead to cirrhosis, liver cancer, and death

Young children under five years of age are more likely to have no symptoms of infection, but they are still infected and contagious; thus their contacts will be unaware of exposure

If you were led to believe that you could wait until your child is ten years old, then you have not been fully informed by your paediatrician. Again, you may make that choice, but how will you feel when your child shares utensils with or is scratched or bitten at pre-school, only to find out later that the other child is a hepatitis B carrier?

MMR should not and cannot be administered as three separate injections

The single antigen doses are no longer manufactured

This is not a "multi-dose" vial, but a triple antigen vial

Separating the injections will cause more pain to the child and puts the child (and others, including pregnant women who may be exposed to them) at increased risk of getting the diseases (four to six persons out of 100 who get mumps will get meningitis and four of ten adult males will get inflammation of the testicles that can lead to sterility; rubella can cause devastating birth defects if contracted during pregnancy, including congenital heart defects, mental retardation and deafness)

There is no scientific evidence for a benefit in separating the vaccines. In fact, this notion comes from one doctor's speculation about the potential benefit to separating the vaccines in discussions with the media. He never published this reasoning in a scientific journal nor have any of his co-investigators made similar assertions.

Thimerosal in vaccines has not been linked to autism or any other neurotoxic effects

Thimerosal is a mercury-containing compound used in vaccines since the 1930's as a preservative and bactericidal, usually in multi-dose vials

It was present in some, not all vaccines, up to 1999-2000 (and has never been in MMR)

l None of the vaccines in the current recommended schedule have thimerosal (I wonder when Dr. Mercola's website will correct its fallacy in this regard)

Symptoms of mercury toxicity are not the same as autism

The FDA called for a review all mercury-containing foods and drugs in 1997. Although there was no evidence for adverse effects from thimerosal except local hypersensitivity reactions, the AAP, US Public Health Service and vaccine manufacturers agreed that thimerosal-containing vaccines be removed. Another balance of risks and benefits; fortunately the removal of thimerosal has simply led to increased manufacturing costs and potential harm to the environment due to the increased packaging of individual dose vials.

l Mercury is present in the environment and everyone is exposed to small amounts

The primary environmental exposure to organic mercury is consumption of predator fish such as swordfish and shark. All canned tuna contains small amounts (an average of 17 micrograms per six ounces).

Ms Thorne, the chance of your child being harmed from eating tuna sandwiches is very low, but he will be exposed to some mercury. The risks of exposure to mercury from fish have to be balanced with the health benefits of eating fish. Again, life has risks, but risks must be balanced against the benefits.

The Vaccine Adverse Effects Reporting System (see www.vaers.org)

Is a passive surveillance system that monitors unverified reports of health events, both minor and serious, that occur after vaccination.

Many of these events may be temporally associated with the vaccine, not caused by the vaccine. Extensive research then looks into these relationships.

Any Internet site or media report that presents VAERS reports as "verified" cases of vaccine deaths and injuries are misrepresenting the nature of this system.

There are more than ten million vaccinations given annually in the US to children under one year. If there were no new combination vaccines, the number would be closer to 50 million injections. For 1,600 "incidents" to be listed is a rather low incidence of adverse events.

l Haemophilus influenza type b (H. flu) caused 20,000 cases of meningitis and other life-threatening infections and killed 600 children annually in the US before the Hib conjugate vaccine was approved in 1990 (most were under one year of age). Many that survived were left with deafness, seizures, or mental retardation. Those are adverse events worth worrying about.

Consumers need to develop a healthy scepticism and watch for red flags when evaluating reports of medical advances and possible problems.

To evaluate media reports and Internet sites about health care, a person should consider these questions:

4What is the source of the information?

Good sources of information include medical schools, government agencies (such as the NIH or the CDC), professional medical associations (such as the AAP), and national disorder/disease-specific organisations (such as the National Alliance for Autism Research). Information from studies in reputable peer-reviewed medical journals is more credible than popular media reports.

4Who is the authority?

The affiliation and relevant credentials of "experts" should be provided, although initials behind a name do not always mean the person is an authority. Reputable medical journals now require researchers to reveal possible conflicts of interest - such as when a researcher conducting a study also owns shares in the company marketing the treatment being studied.

4Seek standard scientific procedure vs. limited case studies and testimonials

The scientific approach involves testing in carefully controlled conditions, with enough subjects to allow the researchers to be comfortable with the "strength" of their findings. Good scientific studies go through peer review before they are published in a scientific journal (the research is analysed by a group of professionals with expertise in a specific scientific or medical field).

Finally, findings are not considered substantive until additional studies by other researchers have been conducted to reaffirm (or refute) the findings. In the second method of evaluation, conclusions are drawn from a limited sample size and are often based on testimonials from doctors or patients. There is generally no control group, peer review, or replication of findings.

This raises questions about the validity of the statements.

4Is the finding preliminary or confirmed?

Unfortunately, a preliminary finding is often reported in the media as a "breakthrough" result. One should track the result over time and seek out the original source, such as a professional scientific publication, to get a fuller understanding of the research findings.

The stunning growth of the Internet has placed knowledge and information at our fingertips, and can be a valuable source of medical information. The bad news is that with its low cost and global entry, the web is also home to a great deal of dubious health information.

In addition to the tips just mentioned, web surfing requires special considerations:

4Know where you are

Part of the address tells you what kind of domain owns the host computer

e.g. .edu. = university, .com = company (usually commercial), .org = non-profit organisation, .gov. = government agency

4 You can obtain a "second opinion" regarding information on the web

Pick a key phrase or name and run it through a search engine to find other discussions of the subject, look for a link to the original data/study, or talk to your health care professional.

4Be wary of sites with online advertising

While it may appear the site is genuinely interested in your health, the real motive may be to solicit you as their patient or you sell their products. Be especially wary if products are described as "miraculous" or an "astonishing breakthrough", or claims they will work for everyone with the condition.

An example of a website with dubious health information is the one Ms Thorne recommends in her letter (www.mercola.com). While some of the health information may be accurate, much of the material is intentionally misleading and thus confusing to the average consumer. It was quite difficult to find Dr. Mercola's credentials. He is an Osteopath (not a MD), and provides a long list of "publications" which are mostly letters to editors of obscure journals. The website encourages you to become his patient and offers products to purchase, although he claims to have no monetary interest in doing so.

He offers mostly testimonials and limited case studies to back up his claims, without providing sources of information from reputable, peer-reviewed scientific journals. The more than 200 articles Ms Thorne refers to are all from his website, and are virtually all personal affidavits from parents or doctors, letters to or articles from newspapers and other lay magazines, and commercially sold books. Only a few were based on peer-reviewed journals like the New England Journal of Medicine. Much of the information is based on manipulation of statistics, and would be difficult to interpret other than by a person very knowledgeable about the real science.

Ms Thorne, I am glad to read you are not "anti-vaccine", but I worry about public reliance on "scientific" information from websites such as the one you recommend.

Amazingly, one referenced source is a publication from 1904 "A Summary of the Proofs that Vaccination Does Not Prevent Smallpox" from the National Anti-Vaccination League. How ironic that 100 years later we are having the same debate, without Dr. Mercola acknowledging that smallpox claimed 300 million lives in the 20th Century alone, more than killed in all wars combined (most that survived were scarred or blind). The last natural case of smallpox was in 1977 in Somalia. Smallpox has been eradicated worldwide due to the success of immunisation.

Some excellent Internet sites about immunisations readers should look at are

www.immunizationinfo.org

www.cdc.gov./nip

www.cispimmunize.org

Childhood immunisations have been one of the most important medical advances of the 20th century, if not in the entire history of medicine. But the success of immunisation programmes has created an interesting irony: many parents (and doctors) have never seen these diseases and the suffering they can cause and, therefore, are less concerned about the need to immunise. We cannot afford to become complacent about immunisations, lest we allow history to repeat itself.

@EDITRULE:

Bente Lundh, MD Fellow of the American Academy of Pediatrics, is a paediatrician and member of the Bermuda Advisory Council on Immunisation Practices.