Immunization and the Effects of Polio and Rubella in the US
from the 20th to the 21st Centuries
Charles Grose, MD, Professor and Director, Division of Infectious Disease
Department of Pediatrics, University of Iowa
Fall 2004 

Polio Poliovirus has been recognized for centuries. Until the mid 1800s, it was an endemic disease; that is, it was continually present in the US. Beginning in the late 1800s, it became an epidemic disease with many more cases appearing than were expected.

Prior to the introduction of a polio vaccine in the US, epidemics occurred every summer. From 90-95% of infected children had no symptoms, while 5-10% had signs ranging from aseptic meningitis to paralysis. The most feared complication, paralysis, probably occurred in only 1-2% of all infected children, especially those between 5-14 years of age. Legs were affected more often than arms. The most severe cases also had paralysis of the respiratory muscles, requiring treatment in the familiar iron lung machine. On average, the decade of the ’50s saw about 20,000 cases of paralytic polio each year.

Dr. Jonas Salk produced the first polio vaccine. This inactivated polio vaccine (IPV) was licensed in 1955 and immediately accepted by the general public because of the great fear of paralytic poliomyelitis. Live attenuated polio vaccine, the “oral polio vaccine” (OPV), was produced by Dr. Albert Sabin and licensed in 1961.

One of the reasons that the Public Health Service switched from the Salk vaccine to the Sabin vaccine in the 1960s had to do with herd (or community) immunity. Among those in the US who had not received the Salk vaccine, outbreaks of polio continued to occur. In contrast, shortly after the introduction of the Sabin vaccine, there was clear evidence that vaccination of a population with a live attenuated virus also protected children who were not immunized.

Immunization with the Sabin vaccine virtually eliminated wild type poliovirus in the USA. However, one rare but severe adverse effect of the Sabin vaccine became increasingly apparent: A handful of paralytic cases occurred in the US each year due to infection with the vaccine virus itself. The medical-legal consequences were increasingly onerous to the pharmaceutical industry, and after much debate, the Public Health Service in the US switched back to the Salk vaccine.

In the meantime, the Sabin vaccine has been successfully used in Mexico, Central America, and South America to eliminate wild type poliovirus. A similar effort to eliminate poliovirus worldwide has been mounted over the last decade.

However, this effort is floundering in Africa because of religious disputes in predominantly Muslim countries. In 2003-2004, a resurgence of poliovirus occurred in Nigeria, which is now exporting poliovirus to many other African nations. It is possible that international travel will re-introduce poliovirus to Europe and the United States, and for that reason immunization against polio continues to be a crucial component of preventive health care.

Rubella
The eradication of rubella – “German measles” or “three-day measles” — is one of the major accomplishments in the history of vaccination in the United States. In the past, rubella epidemics tended to occur on a worldwide basis about every 10 years. The Centers for Disease Control report that during the decade before the introduction of rubella vaccination, the US saw an average of 530,000 cases a year.

The largest rubella epidemic in the United States occurred in 1964-1965, and resulted in the birth of an estimated 30,000 infants with congenital rubella syndrome. As many as 85% of pregnant women with clinical rubella delivered babies with congenital rubella. The highest percentage of congenital rubella occurred when the pregnant mothers had rubella during the first trimester.

The percentage fell to 50% during the second trimester, and was virtually nil in the third trimester. Many pregnant women who were unaware of having had rubella during this epidemic also delivered infants with congenital rubella syndrome. Conditions associated with classic congenital rubella include cataracts, deafness, bleeding tendency, hepatosplenomegaly, and growth retardation.

The first rubella vaccine was developed in the 60s. Early studies noted that 10 to 20 days after vaccination, immunized children shed small amounts of rubella vaccine virus. However, unvaccinated siblings did not contract the virus. In other words, unlike live polio vaccine, rubella vaccine virus was not transmissible to susceptible contacts.

Rubella vaccine was licensed in the United States in 1969. Over the following decade, the number of cases of rubella and congenital rubella syndrome dropped markedly. By 1977, there were only 18 reported cases in the United States, and the number has remained remarkably low over the past 20 years. Today, the rubella vaccination is usually administered as part of the MMR (measles/mumps/rubella) vaccine.

No worldwide effort to eradicate rubella has been mounted. Occasional cases of rubella have been noted recently in the US, mainly in recent immigrants from Mexico and Central America who may not have been immunized as children. In Mexico, for example, immunization for rubeola (measles) is widely available, while rubella (or MMR) vaccination is not as widely administered. For this reason, vaccination against rubella continues to be important.

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