2002 News Archive

New study shows that administration of vaccines containing thiomersal does not raise blood concentrations of mercury above safe levels in full-term infants

The study, which investigated the concentrations of mercury in the blood, urine and stools of full-term infants after the administration of routine childhood vaccines containing thiomersal, was published in November 2002. It found that the administration of these vaccines did not appear to raise blood concentrations of mercury above safe levels in infants and that thiomersal was eliminated rapidly from the body after vaccination. This provides reassurance about the safety of thiomersal as a preservative in childhood vaccines.

This study was carried out by Pichichero and colleagues in the USA and published in The Lancet Journal.  The authors studied two groups of full-term infants (61 in total), one group who received thiomersal-containing vaccines and a second group who received thiomersal-free vaccines.  The former group comprised 20 full-term infants aged 2 months and 20 aged 6 months and the latter comprised 21 infants.  The study took place at routine vaccination visits in two centres in the USA between November 1999 and October 2000.  The concentration of thiomersal in the infant's blood, urine and stools was examined at 3 to 28 days after vaccination. 

Thiomersal remained in the blood of infants for only a short period of time (3 to 10 days) after vaccination indicating rapid excretion.  The mean blood mercury in two month olds who received thiomersal-containing vaccines was 8.20 parts per billion (Range: 3.75 to 20.55 parts per billion).  In 6 month olds who received thiomersal-containing vaccines, the mean blood mercury value was 5.15 parts per billion with all recorded values lower than 7.5 parts per billion.  These blood concentrations of mercury are less than 29 parts per billion which is the concentration thought to be safe in umbilical cord blood when the foetus is in utero. Concentrations of mercury were low in the urine of infants who received thiomersal-containing vaccines but high in the stools indicating rapid excretion.   

The study found that the amounts of mercury in the blood of infants receiving vaccines containing thiomersal are well below levels potentially associated with toxic effects.  The authors concluded that thiomersal in routine vaccines poses very little risk to full-term infants.

New studies show no link between MMR and autism

The first study was carried out by Makela and colleagues in Finland and published in the journal Pediatrics. The authors examined the records of over 500,000 Finnish children who had received MMR and looked at whether or not these children were admitted to hospital for aseptic (i.e. viral) meningitis, encephalitis or autism. MMR is known to protect against encephalitis due to measles, mumps and rubella. The authors found that aseptic meningitis rates decreased by 35% and encephalitis rates by 25% after the introduction of MMR. 

The authors did not find any association between hospitalisation for autism and time since vaccination with MMR. None of the 309 children identified in the study with autism were admitted to hospital at any time because of inflammatory bowel disease. 

While these results add to the already large body of evidence showing no association between MMR and autism this study has some limitations, as identified by the authors. The main one is that they only looked at hospital admissions. Thus they might have missed children with autism who were not admitted to hospital. However they do point out the hospital admission is a common part of the initial management of autism in Finland.

The second study, published in the New England Journal of Medicine, is even more comprehensive. Madsen and colleagues studied all children born in Denmark between 1991 and 1998. The vaccination records of over 500,000 children were examined. They also looked at the admission records of psychiatric hospitals, psychiatric departments and outpatient departments to identify cases of autism and autism spectrum disorder (ASD). There are a number of factors specific to Denmark relevant to this study: autism can only be diagnosed by child psychiatrists, children with suspected autism are routinely referred to such specialists and there is a virtually complete reporting of childhood vaccination. These factors, combined with the fact that the authors were able to examine results for all children born in Denmark, make this a very robust study.

Madsen and colleagues found that the risk of autism was the same in vaccinated and unvaccinated children. They also found that there was no association between the age that MMR was given, time since vaccination or the date of vaccination and the development of autism. There was no evidence to suggest that there could be a subgroup of children who are particularly at risk of developing autism after MMR.

All of the studies published to date that have investigated possible links between MMR and autism have found no association. The study by Madsen and colleagues was very well-designed and extremely comprehensive and probably represents the best evidence yet that there is no association between MMR and autism.

MMR versus Separate Single Vaccines for Measles, Mumps and Rubella

Some people have suggested that children should be vaccinated against measles, mumps and rubella using separate single vaccines, rather than the combined MMR vaccine. This is based on the supposed link between MMR vaccine and autism spectrum disorders (ASD). The theory is that because MMR contains three different components it somehow "overloads" or weakens the child's immune system, making them more susceptible to developing ASD. 

Parents are understandably concerned when links are suggested between a vaccine and a devastating disease such as ASD. Even if the link were only theoretical, giving the three vaccine components separately would seem to be a sensible precaution. The evidence, however, suggests otherwise:

There is no evidence of any association between MMR and ASD
The original supposed link between MMR and ASD was based on a study by the Inflammatory Bowel Disease Study Group (IBDSG), at the Royal Free Hospital in London.¹ They described 12 children with ASD where the onset of ASD apparently coincided with receiving the MMR vaccine. The original study stated: "We did not prove an association between measles, mumps and rubella vaccine and the syndrome described". Further studies, including ones carried out by the IBDSG, have not shown any link between MMR and ASD.²

One study, by Kaye et al, found that there was a significant increase in reported cases of ASD in the UK between 1988 and 1999. However, the rate of MMR vaccination remained the same throughout this period. Thus the increase in ASD cases could not be explained by exposure to MMR.³ Another study, by Dales et al, compared the number of cases of ASD with rates of MMR vaccination in California from 1980 to 1994. Again they found a large increase in the incidence of ASD, but only a small increase in MMR vaccination rates. The small increase in MMR rates could not explain the increase in ASD. Furthermore they found that the large increase in ASD incidence occurred before the small increase in MMR vaccination rates.⁴

Seven international expert groups have reviewed the evidence relating to MMR and ASD. They were all unanimous in their conclusions that the current evidence does not support a link between MMR and ASD.⁵

Combination vaccines do not overload or weaken the immune system
The MMR vaccine contains 24 different antigens (the chemicals that stimulate the immune system to produce immunity to viruses and other foreign substances). This number of antigens is minute compared to the total number that the immune system is capable of responding to (up to 100,000,000,000).⁶ Indeed there are fewer antigens in all of the current childhood vaccinations combined then there were in either the single smallpox or older pertussis (whooping cough) vaccines. Likewise we are all exposed to hundreds of times as many antigens every day, in the food we eat, the water we drink and the air we breathe.

Vaccines are designed to strengthen the immune system, not weaken it. In one study from Germany it was found that vaccinated children were not only protected against the diseases for which they had received the vaccines, but also had fewer infections with other bacteria and viruses compared to non-vaccinated children. This was thought to be due to an overall boosting of the immune system by vaccines.⁷

On the other hand infections with bacteria and viruses often make children more prone to infection with other bacteria or viruses. Measles infection often leads to other infections, such as pneumonia and middle ear infections.

Using three separate vaccines is untested, untried and raises too many unanswered questions
The use of three separate vaccines for measles, mumps and rubella has never been used in any country in the world. There have been no studies done to determine whether or not this approach is safe or effective. Likewise there is no experience with using this approach. This raises a number of unanswered questions: Is this approach safe? Will it protect children against these diseases? What order should the vaccines be given? How much time should be taken between vaccine doses?

In contrast the MMR vaccine has been in use for over 30 years and underwent rigorous studies to ensure that it was safe and effective before it was released for general use. The combined research evidence and decades of experience with MMR has confirmed that it is safe and effective. Indeed, the World Health Organisation recently concluded that MMR is one of the safest vaccines ever produced.

Using three separate vaccines may be less effective and cause more side effects than MMR
The three separate vaccines do not have as long or as rigorous a safety record as MMR. Some varieties of the individual mumps vaccine, in particular, give cause for concern. Some mumps vaccines may contain the Rubini strain of the virus, which was found to be ineffective. Others may contain Urabe strain, which is associated with an increased risk of viral meningitis.²

Separating the vaccines leaves a child exposed to the risk of infection
Leaving a gap between the individual measles, mumps and rubella vaccines means that children are at risk of acquiring one of the other infections before they receive the next vaccine.

Separating the vaccines requires six injections
Two doses of measles, mumps and rubella vaccine are required to ensure maximum protection against these diseases. This means that giving them separately will require six trips to the doctor and six separate injections. Apart from the difficulty of organising six separate visits to the doctor this means that children will have to have an extra four injections unnecessarily. Combining the three vaccines together in the MMR vaccine means fewer traumas for children and fewer visits to the doctor. 

MMR is a safe vaccine and protects children against potentially devastating infections. It also prevents the weakening of the immune system that occurs with natural infections. Giving the three vaccines separately is less effective and may be less safe. Given that we have a proven safe, effective vaccine, backed up by more than 30 years experience, it would be unwise to recommend three separate vaccines.

References:

1.  Wakefield AJ et al. Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet 1998; 351: 637-41.
2. Elliman DAC and Bedford HE. MMR vaccine: worries are not justified. Arch Dis Childhood 2001; 85: 271-4
3. Kaye JA et al. Mumps, measles and rubella vaccine and the incidence of autism recorded by general practitioners: a time trend survey. BMJ 2001; 322: 460-3
4. Dales L et al. Time trends in autism and in MMR immunization coverage in California. JAMA 2001; 285: 1183-5
5. Medical Research Council. Review of autism research: epidemiology and causes. Department of Health (UK), 2001
6. Offit PA et al. Addressing parents' concerns: do multiple vaccines overwhelm or weaken the infant's immune system? Pediatrics 2002; 109: 124-9
7. Otto S et al. General non-specific morbidity is reduced after vaccination within the third month of life: the Greifswald study. J Infect 2000; 41: 172-5

Case of Wound Botulism in Ireland

The National Disease Surveillance Centre has been notified of a case of botulism, which has been identified in the Eastern Regional Health Authority. This case is under investigation by the ERHA. It has arisen in an injecting drug user. In February 2002 three cases of botulism were reported in injecting drug users in the UK.

The NDSC and the Department of Health and Children have asked public health doctors and other health professionals to be alert to possible cases of botulism.

Botulism is a rare condition that is caused by botulinum toxin, a poison produced by the bacterium Clostridium botulinum. The bacterium is common in the soil in the form of spores. It usually takes about 12-36 hours to start to develop symptoms once you have been exposed to the toxin. More than 90% of cases are treated successfully but some prove fatal.

Persons with botulism may complain of symptoms such as blurred vision, difficulty swallowing, difficulty in speaking, paralysis and breathing problems. Treatment is with a special botulism antitoxin antidote and antibiotics.

It is possible that this case may be associated with injecting drug use. The advice to those who inject drugs is:

• Never, ever share needles, syringes, cookers/spoons or other 'works' with other users.
• Smoking heroin is less harmful than injecting
• If you must inject, do not inject into muscle or under the skin: make sure you hit the vein - blood kills bugs better than muscle.
• Use as little citric acid as possible to dissolve the heroin. Too much damages skin and muscle and gives bugs a better chance to grow and cause infection.
• If you inject more than one type of drug, don't inject them all in the same place. This is important because some drugs, like cocaine could give any bacteria in heroin a better chance to grow.