Vaccination: Science Versus Perception


The development of vaccines and their application in immunizing populations has led to well-documented control and global reduction of numerous infectious diseases. The benefits of this infection control strategy have proven to be so successful in providing protection against many childhood and adult microbial infections that the US Centers for Disease Control and Prevention (CDC) cited vaccination as the number one public health achievement of the 20th century. I attempt to emphasize this latter statement in seminars by mentioning to the audience that most of us in the room probably would not have been born, or be alive today, were it not for the protection that vaccines have provided over many decades. Despite the accumulation of scientific, clinical, and public health knowledge describing the virtual eradication of a number of life-threatening microbial diseases in the United States and many other countries, concerns are raised by some questioning vaccine necessity, efficacy, and safety. Unfortunately, many of these comments often lack supporting scientific and clinical evidence. As a result, unsubstantiated concerns and misperceptions can cause individuals, including some healthcare providers, to refuse vaccinations for both themselves and their families.
     Like preceding articles in this section, a question-and-answer format is used in discussing the rationale and benefits of immunization, as well as for antivaccine issues and concerns. Since this discussion will consider only a few selected topics, the reader can access additional useful information discussing specific vaccines, immunization protocols, and vaccine safety by referring to the Suggested Reading section at the end of this article.

Table. Decrease in US Cases of Vaccine-Preventable Diseases (CDC)

Percent Reduction


Paralytic polio
Heamophilus influenzae type b

Question 1. How has widespread vaccination of the general population impacted the incidence of many infectious diseases?
The rationale for increasing the role for public health immunizations in the last century was based on the usefulness of vaccines compared to other protective approaches. The latter include: (1) development of natural active immunity after recovering from symptomatic or asymptomatic infection, and (2) therapeutic or prophylactic administration of antimicrobial drugs. The following table published by the CDC in 1999 illustrates the dramatic reversal observed for a number of historical disease scourges as a result of widespread vaccination (Table).
     The global eradication of smallpox, near elimination of poliomyelitis, and > 95% reduction in the incidence of previously common diseases such as measles, mumps, rubella, diphtheria, and tetanus in developed countries has helped to save many lives and contributed to an increase in the well being and life expectancy of their populations. The Advisory Committee on Immunization Practices of the CDC annually reviews recommended vaccination schedules using the most recent scientific and clinical information when considering changes in schedules, vaccine formulations, proposed inclusion of additional approved vaccines, and safety alerts where necessary.

Question 2. The observed public health success of many vaccines is well documented. However, even with this achievement we still have not been able to eliminate any additional vaccine-preventable diseases other than smallpox. Why?
Please remember, routine childhood immunization programs are a primary reason for the demonstrable decline in the incidence of many vaccine-preventable infections. Using a relatively recent example to illustrate, think about how virtually everyone contracted an active case of chickenpox at a young age before 1995. Then the varicella-zoster vaccine (Varivax) became available. Since that year, the annual incidence of this viral infection in the United States has dropped from more than 4 million cases in 1994 to a little more than 30,000 cases in 2008. Unfortunately, certain vaccine-preventable diseases like chickenpox have not been eliminated, in part because a substantial percentage of the recorded disease morbidity and mortality now occurs in adults and adolescents. Thus, healthcare providers and others who have neither experienced natural infection nor been immunized for diseases such as chickenpox, measles, rubella, and mumps are at increased risk for these droplet-mediated infections. In addition, we still see too many people contract other preventable diseases such as Streptococcus pneumoniae pneumonia and influenza despite the availability of safe and effective vaccines. Multiple reasons are given to explain the fact that adults do not have a high vaccination rate, including: (1) common belief that most immunizations are only for childhood diseases; (2) missed opportunities to receive vaccines; (3) lack of perceived risk by individuals for vaccine-preventable infections; (4) misperception that vaccine-preventable diseases have been virtually eliminated; and (5) concerns and fears about postvaccination adverse effects.

Question 3. How safe are vaccines when they become available and are recommended for widespread use?
The answer to this inquiry must begin by stating that vaccination is one of the most effective, widely used, and cost efficient public health strategies for combating infectious diseases. Having said that, it must also be noted that no vaccine is 100% effective or perfectly safe. Even with a > 95% response rate shown for many vaccines, there still are a small percentage of recipients who do not develop protective immune responses postvaccination. Unless they are tested for the presence of induced antibodies and found to be nonresponders, these individuals unknowingly remain susceptible to microbial infection during an outbreak. Thus, when a local epidemic occurs it is not unexpected to find “vaccinated” individuals included in the total disease count.
      With regard to safety, there are a number of features which are consistent for all vaccine programs. A few representative considerations are:
      All vaccines are thoroughly studied and tested before they are licensed for public use. Extensive laboratory investigations are required before any clinical trials are initiated to further evaluate their efficacy and safety. If results are favorable, the US Food and Drug Administration evaluates the data and can approve public release of the vaccine.
     There is a strong multi-check system in place to provide ongoing monitoring of vaccines. This involves a concerted effort by a variety of agencies including federal, state, and local health departments to collect and investigate ongoing information on vaccine safety. Two important monitoring systems here are the Vaccine Adverse Event Reporting System and the Vaccine Safety Datalink project, and members of the public can also submit reports of possible side effects for further investigation.
     As with any other medication, adverse effects can occur following immunizations. The overwhelming majority of these (> 90%) are minor, usually involving a sore arm and/or mild fever. These resolve relatively quickly. Unfortunately, rare serious reactions also can occur. These may be seen in one individual out of hundreds of thousands to millions of vaccine recipients. In some instances, the event may be so rare so that it cannot be appropriately investigated. Thus, the risk from disease versus risk from vaccination must always be evaluated and compared where possible.
The question can also be asked here—what if vaccines were not available? There isn’t any doubt that not only would there would be many more disease cases, but also more serious disease sequelae, including more deaths. Consider the following disease and vaccine adverse sequelae comparison:


  • Six cases in 100 develop pneumonia.
  • One in 1,000 develops encephalitis.
  • Two in 1,000 die from measles complications.


  • One in 300 develop encephalitis.


  • One in 4 pregnant women can give birth to a baby manifesting congenital rubella syndrome, if the woman becomes infected early in the pregnancy.

Measles Mumps and Rubella (MMR) vaccine:

  • One recipient in 1,000,000 develops encephalitis or allergic reaction.

Any instance of a serious event caused by immunization is one too many, but the fact remains that a nonvaccinated child or adult has a far greater life-threatening risk from contracting the disease than from receiving a vaccine. In addition, remember that collected data including adverse reactions are continually analyzed and evaluated for possible vaccine-associated complications.

Question 4. A major argument voiced by many who do not want to receive vaccinations is that some vaccines can cause autism. Are there scientific, clinical, and/or epidemiological data to indicate such a relationship exists?
It is impossible to go into much depth for this topic here with the limited space available. A few selected references are provided at the end of this discussion. Suffice it to say the possible association of autism and vaccination has been a hot button issue since 1998. It was then that a widely publicized article published in The Lancet initially speculated about a possible relationship between autism and receipt of MMR vaccine. This “conclusion” was based on research involving only a few children, the temporal association of MMR childhood vaccination, and recognition of autism in children. The article has subsequently been discredited for a number of reasons, and in 2010 the journal took the dramatic step of officially retracting the article. Fortunately, in the last 10 years, at least 7 to 8 large, controlled studies have investigated this important issue and been published in reputable, refereed journals. Taken collectively, the findings provide strong evidence against the hypothesis that vaccination causes autism. Even though a substantial amount of research has been undertaken investigating this and other possible untoward neurological effects of vaccinations, controversy and heated discussion continue. Numerous sources of information are available. Please avail yourself of the opportunity to study reports and opinions alike, so that you as a health professional can be armed with the best possible documented, credible findings as you are faced with vaccine questions in both your professional and personal life.

In conclusion, none of the currently available vaccines provide absolute protection, nor are they perfect. However, as research continues to discover and study infectious disease risk factors, there is little doubt that effective, safe, next generation vaccines will offer additional opportunities to protect those at risk.


Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. 11th ed. Washington, DC: Public Health Foundation; 2009.

Centers for Disease Control and Prevention. Epidemiology and Prevention of Vaccine-Preventable Diseases. 11th ed. Washington, DC: Public Health Foundation; 2009.

Centers for Disease Control and Prevention, Immunization Safety Office. Activities/ About_ISO.html. Accessed September 29, 2010.

Centers for Disease Control and Prevention. Ten great public health achievements—United States, 1900-1999. MMWR Morb Mortal Wkly Rep. 1999;48:241-243.

Clarkson TW, Magos L, Myers GJ. The toxicology of mercury—current exposures and clinical manifestations. N Engl J Med. 2003;349:1731-1737. 

Harte JA, Molinari JA. Cottone’s Practical Infection Control in Dentistry. 3rd ed. Baltimore, MD: Lippincott Williams & Wilkins (Wolters Kluwer Health); 2009. 

US Food and Drug Administration. Thimerosal in vaccines. Accessed September 29, 2010.

Dr. Molinari is currently director of infection control for THE DENTAL ADVISOR in Ann Arbor, Mich. Previously, he served for 32 years at the University of Detroit Mercy School of Dentistry as professor and chairman of the department of biomedical sciences and director of infection control. He continues serving as a consultant for the CDC, ADA Council on Scientific Affairs, and the Council on Dental Practice. He is currently a member of the Michigan Board of Dentistry. In recognition of his efforts, Dr. Molinari was inducted as an honorary member of the Michigan Dental Association, the International College of Dentists, and the American College of Dentists, and he is a 2009 recipient of the ADA Golden Apple Award. He has published more than 350 scientific articles, text chapters, and abstracts, and he lectures internationally on infectious diseases and infection control. He was the infection control section editor for the Compendium of Continuing Education in Dentistry, a member of the editorial board for the Journal of the American Dental Association, and writes a monthly column for Dental Economics. He can be reached at


Disclosure: Dr. Molinari is a consultant for Hu-Friedy and SciCan.