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MMR VACCINE : Current Issues |
~Dr. P. S Patil
M.D.(Ped), FIAP, Prof & Head, Dept of Pediatrics, MGM Medical
College & Hospital, Aurangabad. 431001.
e-mail : iap.abad@hotmail.com |
Immunizations ranked among the
greatest public health accomplishments during the 20th century
Advances in biotechnology offer substantial promises in
additional disease control through new vaccines, especially
when combined with new funding mechanisms for the developing
world. Increasing public concern about vaccine risks and
vaccine safety, both real and perceived, however, has cast a
shadow over these achievements and possibilities. Vaccines are
being linked to diseases ranging from autism to multiple
sclerosis. In an era of virtual eradication of
vaccine-preventable diseases (VPDs), such safety concerns make
it increasingly difficult to convince the populace to accept
immunizations, raising the spectre of resurgence of VPDs.
Issue 1: Measles, Mumps, Rubella Vaccine and Autism
Autism is a chronic developmental disorder characterized by
problems in social interaction, communication, and restrictive
and repetitive interests and activities. The causes of autism
are unknown in most cases but can be congenital. A suspected
link between measles, mumps, rubella (MMR) vaccine and autism
has been suggested by some parents of children with autism.
The only published evidence to support such an association is
based on a series of 12 patients who had inflammatory bowel
disease and autism. The authors speculated that MMR vaccine
was the possible cause of bowel problems, with resultant
malabsorption of essential vitamins and nutrients leading to
autistic developmental disorders. Substantial concerns,
however, have been raised about the validity of the study. For
example, other pediatric gastroenterology experts have
disputed whether autistic enterocolitis exists. Several of the
children in the case series had autistic symptoms before the
onset of their bowel symptoms, inconsistent with the proposed
pathophysiology.
Moreover, since publication of their original report, the same
investigators published another study in which highly specific
laboratory assays in patients with inflammatory bowel disease,
the posited mechanism for autism after MMR vaccination, were
negative for measles virus. Epidemiologic studies do not
support a causal association between MMR (or other
measles-containing vaccines) and autism. In a population-based
study conducted in London, no association was found between
MMR vaccination and autism diagnosis or developmental
regression. A study of the population of children in two
communities in Sweden also found no evidence of an association
between MMR vaccination and autism
Issue 2: Need for 2nd dose
Not all children receive the first dose of MMR vaccine and in
5-10% of those who do, the vaccine doesn’t work. This means
that each year the number of children who remain susceptible
to measles, mumps and rubella will increase. The second MMR
visit is needed to protect those children who did not respond
to the first dose, and provides an opportunity to give a first
dose to children who didn’t receive the vaccine earlier.
Children who did respond to the first dose get a boost to
their antibodies with a second dose. The second dose of MMR
provides a added safeguard against all three diseases but it
is recommended primarily to prevent outbreaks of these
diseases.
Issue 3: Inclusion of MMR vaccine in the National Immunization
Schedule
The IAP committee on Immunisation feels that MMR is an
important vaccine for inclusion in the National immunization
schedule as it will (i) provide protection from rubella and
thus help in achieving control of congenital rubella syndrome
(CRS). (ii) improve measles control by achieving
seroconversion of those not protected by first dose and by
giving a second opportunity to those who missed the first dose
(iii) achieve control of mumps. The vaccine has also been
shown to be cost effective in developed countries.
However with inclusion of the vaccine in the national
immunization schedule may prove counterproductive in areas
where the vaccine coverage is likely to be between 30%-60% by
increasing the risk of congenital rubella syndrome in such
areas due to epidemiologic shift. The committee therefore
suggests that
• The vaccine should only be introduced in those districts
where primary coverage with the measles vaccine is
consistently more than 80%.
• With the introduction of the vaccine a system for estimating
the burden of rubella / CRS should be simultaneously
instituted so that the impact of vaccination on this burden
may be estimated and any epidemiologic shift detected.
Logistics of such a system have been enumerated in detail in
WHO publications. The vaccine should not be introduced if it
is not possible to institute such a monitoring system.
• In those areas where MMR is introduced in the national
immunization schedule catch up vaccination of all adolescent
girls (11-12 yrs age group) should be done to rapidly reduce
the risk of CRS and counter any epidemiologic shift.
• Once reasonably good coverage has been achieved with the
first dose of MMR there would be a need in future to assess
the need for a second dose of the vaccine at school entry.
Issue 4: Practical Issues
1. How effective is the vaccine?
The level of effectiveness varies for the different components
of the MMR vaccine:
90-95% of people will be immune to measles after the first
dose,
90-95% of people will be immune to mumps after the first dose,
97-99% of people will be immune to rubella after the first
dose.
It is not known why some people don’t get a good response.
Sometimes the vaccine may have been improperly stored, or the
viruses had lost their potency
2. How long does a child remain immune after receiving the
vaccine?
There is very little evidence that immunity to the measles,
mumps or rubella vaccines wanes with time. It is known that
children will remain immune for at least 27 years against
measles, 18 years against rubella and 14 years against mumps
-in other words for the amount of time that the vaccines have
been available. Even if individuals are not fully protected,
the immune system will have some memory and be able to respond
more quickly in the immunised than in those who have not been
immunised. Immunised children with low levels of antibodies
are likely to have a modified, less serious, illness.
Long-term studies on the duration of protection are
continuing. The immunity against infection has been shown to
last such a long time without waning that, in those people
with
protection, it is likely to be lifelong.
3. Is giving three live vaccines too much for an infant’s
immune system to cope with?
Babies and young children are exposed to a large number of
different viruses and bacteria each day and their immune
systems cope extremely well. A recent paper by Offit et al
reviewed the effect of vaccines on the infants’ immune system
and the capacity of the immune system of an infant to respond
to multiple vaccines. This paper concluded that ‘Current
studies did not support the hypothesis that multiple vaccines
overwhelm, weaken or “useup” the immune system’. They point
out that vaccines may actually prevent ‘weakening’ of the
immune system by natural infection and prevent secondary
bacterial infections or complications following natural
infection. It has been estimated that the immune system of
each infant would have the theoretical capacity to respond to
around 10,000 vaccines at any one time. In reality, of course,
children receive nowhere near this number of vaccines. It has
been predicted that if 11 vaccines were given to an infant at
one time, then about 0.1% of the immune system would be ‘used
up’.
4. Adverse reactions of MMR Vaccine
Nearly all children who get the MMR vaccine (more than 80%)
will have no side effects. Most children who have a side
effect will have only a mild reaction.
• Fever 5%-15%
• Rash 5%
• Joint symptoms 25%
• Thrombocytopenia <1/30,000 doses
• Parotitis rare
• Deafness rare
• Encephalopathy <1/1,000,000 doses
5. Contraindications and Precautions
• Severe allergic reaction to vaccine component or following
prior dose
• Pregnancy
• Immunosuppression
• Moderate or severe acute illness
• Recent blood product
6. Vaccine Storage and Handling
• Store 35o - 46oF (2o - 8oC) (may be stored in the freezer)
• Store diluent at room temperature or refrigerate
• Protect vaccine from light
• Discard if not used within 8 hours reconstitution
7. MMR Vaccine and HIV Infection
• MMR recommended for persons with asymptomatic and mildly
symptomatic HIV infection
• NOT recommended for those with evidence of severe immuno-
suppression
• HIV testing before vaccination is not recommended
• MMRV not approved for use in persons with HIV infection
8. MMR Vaccine and Egg Allergy
• Measles and mumps viruses grown in chick embryo fibroblast
culture
• Studies have demonstrated safety of MMR in egg allergic
children
• Vaccinate without testing
Further reading:
1. Immunizations and Autism: A Review of the Literature. Doja
A, Roberts W.
Can J Neurol Sci. 2006; 33(4):341-6
2. Relationship between MMR Vaccine and Autism. Klein KC,
Diehl EB. Ann Pharmacother. 2004; 38(7-8):1297-300
3. 10-minute consultation: MMR immunization. Anthony
Harnden,Judy Shakespeare. BMJ 2001;323;32
4. MMR: where are we now? David Elliman, Helen Bedford. Arch.
Dis. Child. 2007;92;1055-1057 |
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