July 1999
WASHINGTON, D.C. - In the world of infectious diseases, there are few successes as great as the success that vaccines have had in controlling disease. Immunizations have made many diseases from smallpox to polio to congenital rubella and Haemophilus influenzae type b meningitis fodder for grand rounds, rather that common occurrences encountered by physicians.
Yet, America may be on the verge of becoming a victim of this success, explained Bruce A. Gellin, MD, MPH, because people may become complacent about the importance of immunizations if they do not perceive a threat from disease that was rampant just a generation ago. There is an ebb and flow between disease and vaccines, which follows a distinct pattern, Gellin explained at a recent press conference sponsored by the National Foundation for Infectious Diseases.
The pattern, dubbed the "natural history of an immunization program" by Robert Chen, MD, is based on the perception of the disease in the context of the perception of the vaccine. Before a vaccine becomes available, people feel threatened by the disease, especially if the disease is communicable and not easily treatable. Once a vaccine is developed and becomes widely used, the number of cases and outbreaks decrease and a sense of security develops.
With continued use of the vaccine, disease declines and the social disruptions of the disease fade from memory. Although the organism that causes the disease has not disappeared, it is no longer perceived as a threat because the disease is no longer present to the degree it once was. "The unfortunate result is creep of complacency about the need for immune protection by vaccination," said Gellin, staff director of the Vaccine Initiative, an independent resource providing balanced and scientific information about immunizations.
At the same time, with the increased use of vaccine, common side effects and even rare adverse events associated with a vaccine become more prominent. As vaccination becomes more common, events that occur around the time of the administration of a vaccine may seem to be a cause-and-effect relationship. "Who hasn't heard someone say that they got the flu from the influenza vaccine?" asked Gellin, noting that there are a vast number of respiratory pathogens that circulate during the cold and flu season that would not be prevented by the influenza vaccine. "This same phenomenon may be acting when people attribute a whole host of ailments and illnesses to prior receipt of a vaccine."
People stop vaccinating, and a group of susceptibles emerges, often in adolescents or adults. "You introduce these germs, which know no borders and they find the susceptibles and you have an outbreak. Then people say, `Oh yeah, these diseases really do exist,' and people start vaccinating again," said Gellin.
"We need to try and prevent outbreaks from reminding us about the importance of vaccination," Gellin said. This pattern of behavior is not just theoretical. A recent study in The Lancet 1998) by Eugene Gangarosa, MD, of Emory University documented several countries in Europe and Asia where safety concerns about the whole-cell pertussis vaccine led to a decline in the rate of pertussis vaccination and a subsequent increase in epidemic pertussis.
In addition to concerns about common and rare side effects, it seems that a hypothesis becomes a fact merely because somebody thought of it. "As a result, unproved allegations about the adverse events associated with a vaccine take on a life of their own, even without supporting data," said Gellin. These hypotheses need to be tested and qualified or unqualified by the scientific method, but the public does not give that a chance to happen or does not believe the results if they prove the hypothesis false.
The problem becomes society's perceived risk vs. the perceived benefit. If society believes that many children will become severely ill and die from a disease, they see the vaccination risk as small vs. the need to protect their children. If the likelihood that their children will become infected with a serious disease is small, then they perceive adverse events linked to a vaccine as a greater risk, and stop vaccinating their children.
The childhood immunization schedule is complex, and "most of the action takes place in the first 12 months," Gellin explained.
"When you think about this in the context of adverse events or the perception of adverse events, you can see that there is so much going on in the first year of life that if anything goes wrong, you can see how someone would say, my child was fine until he was vaccinated yesterday, an hour ago, two weeks ago, two months ago or whatever. Frankly, you are within a couple of months of being vaccinated [anytime] in the first 12 months of life."
These coincidences have eroded confidence in vaccine and fostered the growth of many antivaccine groups, which spread misinformation about vaccinations. Consequently, wary parents choose not to vaccinate their children.
"When the etiology of a disease is not known, there are often many theories about what may be the cause," Gellin said. "Vaccinations are often pointed to as the `cause' of a wide range of diseases including asthma, attention deficit disorder, autism, chronic fatigue syndrome, diabetes, infantile spasms, inflammatory bowel disease and sudden infant death syndrome, among others. Yet, no data have proved that immunizations cause any of these illnesses," he added.
"If you are the person who says `I was fine until I got this vaccine, then my whole world fell apart,' it is hard to convince you that the two events were related in time but one did not necessarily cause the other. That is why it is important to look beyond the anecdote to well-conducted population-based studies to see whether there is a change in the pattern of some of these diseases following immunizations. And so far, the studies that have looked at that have not demonstrated a causal link."
Another common concern is that the immune system is overloaded by too many vaccines, which may cause some of the above mentioned problems. Not so, Gellin said. "The immune system has an incredible ability to handle all kinds of exposures. We may have a more vivid recollection of going to the doctor's office for a shot, but we may not remember that we sat next to someone in a coffee shop who was coughing and sneezing, that we inhaled exhaust from a bus, or that we were in the park on a day with a high pollen count. The immune system is bombarded with a wide range of exposures all the time. That's why it's there."
Rumors abound that there are "hot lots" of reactogenic vaccines, and parents should be aware of this phenomenon. "With the single exception of the Cutter incident when the Salk polio vaccine was not fully inactivated, there has never been a lot of vaccine recalled because it was `hot.'" There have been recalls of batches of vaccines that were suboptimal or subpotent on routine testing, but not because they were found to be more reactogenic than predicted by the studies conducted prior to licensure," Gellin said.
Many people, including doctors do not think that some diseases are serious enough to warrant a vaccine. Varicella vaccine is a prime example of this. Gellin said some parents have "chickenpox parties," and intentionally expose their child to this disease. "This is fine for the survivors, and I think Darwin taught us something about being exposed to something and surviving."
Many doctors who don't give varicella vaccine have no idea that there are 15,000 hospitalizations each year from varicella and there are 100 deaths, mostly in kids who have normal immune systems. "Usually if they hear these stories, or if they happen to get someone in their practice who develops flesh eating bacteria, that will change their style," he said.
"The best policy is crafted by the best science so we must rely on the evidence - the data that is collected in a rigorous and methodical way - to continue to guide us. At the same time, we must remain sensitive to the concern that our patients may raise about something they read in the paper, saw on the television or downloaded from the Internet. We need to help them to distinguish hypothesis from fact and provide them with the facts they need to help them make informed decisions about immunizations," Gellin said. Physicians are the first line of defense against these rumors, Gellin said, and parents will listen if they are told by their doctor that vaccines are safe, effective and necessary to control disease.
For more information:
- The Vaccine Initiative is a special educational program of the Infectious Diseases Society of America and the Pediatric Infectious Diseases Society. This program is supported by a grant from the Robert Wood Johnson Foundation and serves as an independent source of scientific information about immunizations.
- Gangarosa EJ, Galazka AM, Wolfe CR, et al. Impact of anti-vaccine movements on pertussis control: the untold story. Lancet.1998;351(9099):356-61.
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