Vaccine Safety: Six Common Misconceptions

by CDC

Most parents today have never seen a case of diphtheria, measles, or other once-common diseases now preventable by vaccines. As a result, some parents wonder why their children must receive shots for diseases that don't seem to exist. Myths and misinformation about vaccine safety abound and can confuse parents who are trying to make sound decisions about their children's health care.

Vaccination is a common, memorable event, and association of events in time often signals cause and effect. While some of the sickness or reactions that follow vaccination may be caused by the vaccine, many are unrelated events that occur by coincidence after vaccination. Therefore, the scientific research that attempts to distinguish true vaccine side effects from unrelated, chance occurrences is important.

A great deal of information about vaccinations is available to parents. This is good, because parents should have access to any information that will help them make informed decisions about vaccination. However, information is sometimes published that is inaccurate or can be misleading when taken out of context.

The purpose of this pamphlet is to address six common misconceptions about vaccination that are often cited by concerned parents as reasons to question the wisdom of vaccinating their children. If we can respond with accurate rebuttals perhaps we can not only ease their minds on these specific issues but discourage them from accepting other anti-vaccine "facts" at face value. Our goal is not to browbeat parents into vaccinating, but to make sure they have accurate information with which to make an informed decision.

1. Diseases had already begun to disappear before vaccines were introduced, because of better hygiene and sanitation.

Statements like this are very common in anti-vaccine literature, the intent apparently being to suggest that vaccines are not needed. Improved socioeconomic conditions have undoubtedly had an indirect impact on disease. Better nutrition, not to mention the development of antibiotics and other treatments, have increased survival rates among the sick; less crowded living conditions have reduced disease transmission; and lower birth rates have decreased the number of susceptible household contacts. But looking at the actual incidence of disease over the years can leave little doubt of the significant direct impact vaccines have had, even in modern times. Here, for example, is a graph showing the reported incidence of measles from 1950 to the present.

There were periodic peaks and valleys throughout the years, but the real, permanent drop coincided with the licensure and wide use of measles vaccine beginning in 1963. Graphs for other vaccine-preventable diseases show a roughly similar pattern, with all except hepatitis B showing a significant drop in cases corresponding with the advent of vaccine use. Are we expected to believe that better sanitation caused incidence of each disease to drop, just at the time a vaccine for that disease was introduced?

The incidence rate of hepatitis B has not dropped so dramatically yet because the infants we began vaccinating in 1991 will not be at high risk for the disease until they are at least teenagers. We therefore expect about a 15 year lag between the start of universal infant vaccination and a significant drop in disease incidence.

Hib vaccine is another good example, because Hib disease was prevalent until just a few years ago, when conjugate vaccines that can be used for infants were finally developed. (The polysaccharide vaccine previously available could not be used for infants, in whom most of cases of the disease were occurring.) Since sanitation is not better now than it was in 1990, it is hard to attribute the virtual disappearance of Hib disease in children in recent years (from an estimated 20,000 cases a year to 1,419 cases in 1993, and dropping) to anything other than the vaccine.

Varicella can also be used to illustrate the point, since modern sanitation has obviously not prevented nearly 4 million cases each year in the United States. If diseases were disappearing, we should expect varicella to be disappearing along with the rest of them. But nearly all children in the United States get the disease today, just as they did 20 years ago or 80 years ago. Based on experience with the varicella vaccine in studies before licensure, we can expect the incidence of varicella to drop significantly now that a vaccine has been licensed for the United States.

Finally, we can look at the experiences of several developed countries after they let their immunization levels drop. Three countries - Great Britain, Sweden, and Japan - cut back the use of pertussis vaccine because of fear about the vaccine. The effect was dramatic and immediate. In Great Britain, a drop in pertussis vaccination in 1974 was followed by an epidemic of more than 100,000 cases of pertussis and 36 deaths by 1978. In Japan, around the same time, a drop in vaccination rates from 70% to 20%-40% led to a jump in pertussis from 393 cases and no deaths in 1974 to 13,000 cases and 41 deaths in 1979. In Sweden, the annual incidence rate of pertussis per 100,000 children 0-6 years of age increased from 700 cases in 1981 to 3,200 in 1985. It seems clear from these experiences that not only would diseases not be disappearing without vaccines, but if we were to stop vaccinating, they would come back.

Of more immediate interest is the major epidemic of diphtheria now occurring in the former Soviet Union, where low primary immunization rates for children and the lack of booster vaccinations for adults have resulted in an increase from 839 cases in 1989 to nearly 50,000 cases and 1,700 deaths in 1994. There have already been at least 20 imported cases in Europe and two cases in U.S. citizens working in the former Soviet Union.

About the Author

www.cdc.gov
The Centers for Disease Control and Prevention (CDC) is one of the 13 major operating components of the Department of Health and Human Services (HHS), which is the principal agency in the United States government for protecting the health and safety of all Americans and for providing essential human services, especially for those people who are least able to help themselves.