The more people in a community who are vaccinated, the healthier that community is. Here is how Dr. Samuel Katz, a renowned vaccine expert and a member of PKIDs’ Medical Advisory Board, explained it before Congress in 1999.
“We know too well that the level of [immunization] protection that we have now established in our children and our communities is a fragile one that depends on what we refer to as community or ‘herd’ immunity. From the standpoint of effectiveness, modern childhood vaccines are approximately 90 to 95 percent effective. What that means is that for every 20 children who are vaccinated one or two may not develop a sufficient immune response [or antibodies to fight an infection].
“It cannot be assured that these children will be protected from the virus or bacteria should they encounter it at school, at a playground, at a shopping mall, or at their church daycare. However, if sufficient numbers of children in a community are immunized, the vaccinated ones protect the unprotected by effectively stopping the chain of transmission in its tracks and drastically lowering the probability that the susceptible child will encounter the bacteria or virus,” said Katz.
Community immunity also helps protect children and adults whose immune systems are compromised or weakened because of another illness or old age.
“As long as the great majority of children receive their vaccines, we will be able to maintain our current level of disease control,” Katz explained. “However, should the level of community protection drop to the point where the viruses and bacteria travel unimpeded from person-to-person, from school-to-school, and from community-to-community, we instantly return to a past era when epidemics were an accepted part of life.”
America experienced such an outbreak in 1989-91 with the resurgence of measles. There were 55,622 reported cases mainly in children less than 5 years of age, more than 11,000 hospitalizations and 125 deaths. States do allow personal exemptions, so parents can choose not to vaccinate their children, but those exemptions carry risk to the child and the public’s health, emphasizing the importance of community immunity.
An article in the Journal of the American Medical Association found that, on average, those children who were exempted from immunizations ran a 35-fold greater risk of contracting measles compared to those who were nonexemptors.
Not only are these children at greater risk of disease, their infections can be the spark that ignites a disease outbreak in a community.
According to Dr. Katz, in the late 1960s and early 1970s, despite the availability of a safe and effective measles vaccine, the United States continued to experience regular epidemics of measles. Left to individual choice (as opposed to government mandates), only 60 to 70 percent of the community was immunized.
That coverage failed to provide adequate community immunity to prevent an outbreak.
“States without school immunization requirements had incidence rates for measles significantly higher than states with these requirements,” noted Dr. Katz. “Recognizing these data, other states (not the federal government), quickly adopted similar requirements. These requirements are supported by the American Academy of Pediatrics.
“The results are striking,” he added. “Before we had a measles vaccine, an estimated 500,000 cases of measles were reported each year. In 1998, there were 89 cases of measles in the United States with no measles-associated deaths. Most counties in the United States were free of measles. However, we have learned that nearly all of the cases of measles that did occur in the United States were imported from other countries. This would not have been possible without the “school exclusion” statutes that now exist in every state. While we hear dramatic stories of exotic diseases that are just a plane ride away, the importation of vaccine preventable diseases into a susceptible population is much more frightening. Should we allow our community immunity to wane, we will negate all the progress we have made and allow our communities to be at risk from threats that are easily prevented.”
Compulsory vaccination laws in the United States have repeatedly been upheld as a reasonable exercise of the state’s compelling interest even in the absence of an epidemic or a single case. As the U.S. Supreme Court held in 1905 in the case Jacobson vs. Massachusetts:
“ …in every well-ordered society charged with the duty of conserving the safety of its members, the rights of the individuals in respect of his liberty may at times, under the pressure of great dangers, be subjected to such restraint, to be enforced by reasonable regulations as the safety of the general public may demand.”
The Supreme Court makes clear that “the liberty secured by the Constitution of the United States to every person within its jurisdiction does not import an absolute right in each person to be, at all times and in all circumstances, wholly freed from restraint. There are manifold restraints to which every person is necessarily subject for the common good. [Liberty] is only freedom from restraint under conditions essential to the equal enjoyment of the same right by others.”
This is one in a series of excerpts from PKIDs’ Infectious Disease Workshop. We hope you find the materials useful – the instructor’s text and activities are all free downloads.
Photo credit: lawtonjm