Despite the strong vaccine safety systems in place in the United States, some parents remain concerned about the safety of childhood vaccines and the immunization schedule.
These concerns have led some parents to not allow their children to be
given some or all of the recommended vaccines. Diseases that can be
prevented by vaccines are much more common among children whose parents
have refused one or more vaccines. Specifically, unvaccinated children
are
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23 times more likely to contract pertussis (whooping cough)
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8.6 times more likely to contract varicella (chickenpox)
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6.5 times more likely to contract pneumococcal infections
Children in the United States still die from vaccine-preventable diseases. In 2008, five children developed life-threatening Haemophilus influenza
type B infection in Minnesota, the most since 1992. Three of the
infected children, including one child who died, had been given no
vaccine because their parents had delayed or refused the vaccine.
MMR vaccine and concerns about autism
The public press has reported concerns that the MMR vaccine may cause autism.
These concerns were based on a brief medical report in 1998 about 12
children with developmental disorders such as autism. Their parents
reported that eight of the children had received the MMR vaccine within a
month before they developed symptoms. Because this chain of events
could also have occurred by chance, doctors have since done many studies
to look for a connection between the vaccine and autism. No such
connection was found in any of the studies.
The largest of these studies looked at 537,303 Danish children
who were born between 1991 and 1998. Most (82%) of these children had
been given the MMR vaccine. Doctors found that
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The children who had been vaccinated were no more likely to develop autism than those who were not vaccinated.
Autism or a related disorder occurred in 608 of 440,655 (0.138%)
children who were vaccinated and in 130 of 96,648 (0.135%) of those who
were not vaccinated. The percentage of children who became autistic is
nearly identical in the group that was vaccinated and the group that was
not vaccinated.
Other similar studies from across the world have reached similar
conclusions. In addition, the research in the original widely publicized
study linking autism and the MMR vaccine has been found to have serious
scientific flaws and has been discredited by the medical and scientific
communities.
Thimerosal and concerns about autism
People have also been concerned about possible side effects of
thimerosal. Thimerosal was previously used as a preservative in vials
that contain more than one dose of a vaccine (multidose vials).
Preservatives are not needed in vials that contain only one dose
(single-dose vials), and they cannot be used in live-virus vaccines
(such as rubella and varicella). Thimerosal, which contains mercury, is
broken down by the body into ethylmercury, which is eliminated quickly from the body. Because methylmercury
(which is a different compound that is not eliminated from the body
quickly) is toxic to humans, there was concern that the very small
amounts of thimerosal used in vaccines might cause neurologic problems,
particularly autism, in children.
Because of these theoretical concerns and, although no studies
had shown evidence of harm, thimerosal was removed from routine
childhood vaccines in the United States, Europe, and several other
countries by 2001. (Thimerosal is still used in vials that contain more
than one dose of influenza vaccine and in several other vaccines
intended for use in adults.) The World Health Organization (WHO) has not
recommended its removal from any vaccines because there is no evidence
that routine use causes any harm. The removal of thimerosal from
childhood vaccines has had no effect on the number of children who have
developed autism. Several studies have shown that rates of autism have
continued to increase despite removal of thimerosal from routine
childhood immunizations. This increase, which occurred despite the
removal of thimerosal, provides additional support that thimerosal in
vaccines does not cause autism.
However, people who are still concerned about thimerosal in the
influenza vaccine may ask their doctor to use single-dose vials which do
not contain thimerosal.
Use of several vaccines at the same time
According to the recommended schedule, children should be given
several doses of vaccines against 15 different infections by age 6
years. Because some parents have been concerned about the number of
injections and doctor visits, combination vaccines, such as the diphtheria-tetanus-pertussis vaccine and others, have been developed so that children can receive more vaccines with fewer injections and visits.
However, some parents worry that children's immune system cannot
handle so many antigens given at once. Antigens are the substances in
vaccines that are derived from the virus or bacteria and that cause the
body’s immune system to produce antibodies to fight disease. Sometimes
parents who are worried ask for a different vaccine schedule or ask to
delay or exclude certain vaccines. However, the recommended schedule is
designed to give the various vaccines at the ages when children begin to
need protection against the diseases. Thus, not following the schedule
puts children at increased risk of infection.
Also, vaccines, even combination vaccines, contain very few
antigens. Starting at birth, children encounter dozens and possibly
hundreds of antigens during a single ordinary day. Their immune system
handles these antigens without difficulty. Even a mild cold exposes
children to 4 to 10 virus antigens. The immune system of children is not
stressed or overwhelmed by combination vaccinations.
Effects of vaccine refusal on public health
Delaying or excluding vaccines affects public health. When fewer
people are vaccinated, the percentage of a population that is immune to
disease decreases. Then, the disease becomes more common, particularly
among people who are at increased risk of getting a disease.
People may be at increased risk because
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They were vaccinated but did not become immune.
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They were vaccinated, but their immunity has decreased over time, as may occur as people age.
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Their immune system is impaired by a disorder or a drug (such as the drugs used to prevent cancer or rejection of a transplant), and they cannot be given live-virus vaccines, such as the MMR or varicella vaccine.
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