The Advisory Committee on Immunization Practices (ACIP) has released background information and the rationale for the recommendations on the exclusive use of inactivated poliovirus vaccine (IPV). The report appears in the May 19, 2000 issue of the Recommendations and Reports series of Morbidity and Mortality Weekly Report.
The ACIP recommendations for an all-IPV series went into effect on January 1, 2000. They replace those issued in 1997, which, according to ACIP, were intended to represent a three- to five-year transition policy to an all-IPV schedule. The 1997 recommendations consisted of two doses of IPV at two and four months of age, followed by two doses of oral poliovirus vaccine (OPV) at 12 to 18 months of age and at four to six years of age. According to ACIP, an all-IPV schedule is needed to eliminate the risk of vaccine-associated paralytic poliomyelitis while maintaining population immunity.
In addition to background information that led to the recommendation for an all-IPV schedule, the ACIP report includes data on the epidemiology of poliomyelitis and of vaccination coverage, as well as information on vaccine-associated paralytic poliomyelitis. The following discussion is a summary of the ACIP report.
According to ACIP, the number of cases of paralytic poliomyelitis declined from more than 20,000 in 1952 to an average of eight to nine cases annually from 1980 to 1994. From 1980 to 1998, a total of 152 cases of paralytic polio were reported. Of the 152 cases, 144 were related to use of the poliovirus vaccine. Worldwide, the number of countries where polio is endemic declined from more than 120 in 1988 to approximately 50 in 1998.
ACIP reports that vaccination coverage among children in the United States is the highest ever, largely because of immunization initiatives. Data from the National Immunization Survey show that vaccination coverage with at least three doses of poliovirus vaccine in children from 29 to 35 months of age increased from 88 percent in 1995 to 92 percent in 1996. Vaccination rates were more than 90 percent in 1997 and 1998.
Serologic surveys indicate a high level of immunity among the U.S. population, with more than 90 percent of children, adolescents and adults having antibodies to poliovirus types 1 and 2 and more than 85 percent having antibodies to poliovirus type 3.A 1997–1998 survey of low-income children living in four cities revealed seropositivity for poliovirus types 1, 2 and 3 in 96.8 percent, 99.8 percent and 94.5 percent, respectively.
Vaccine-Associated Paralytic Poliomyelitis
According to ACIP, cases of vaccine-associated paralytic poliomyelitis occurred almost immediately after introduction of the live attenuated poliovirus vaccine. A total of 132 cases were reported from 1980 to 1995. Following introduction of the sequential IPV-OPV schedule in 1997, five cases were reported in 1997 and two cases were reported in 1998. The overall risk of vaccine-associated paralytic poliomyelitis is estimated to be one case in 2.4 million doses of OPV distributed. In persons without immunodeficiency, the risk with the first OPV dose is seven- to 21-fold higher than the risk with subsequent doses.
The All-IPV Schedule
The ACIP report states that adoption of an all-IPV schedule for childhood polio vaccination is intended to eliminate the risk of vaccine-associated paralytic poliomyelitis. Four doses should be given: at two months, four months, six to 18 months and four to six years of age. No additional doses are needed if more time than recommended elapses between doses, such as more than four to eight weeks between the first two doses or more than two to 14 months between the second and third doses. IPV should be used to complete the series in children who have received one or more doses of OPV. IPV can be administered with other recommended childhood vaccines.
ACIP found no evidence to indicate that childhood vaccination coverage declines as a result of the two additional injections. For example, immunization data from Oklahoma, which covered the 18 months from January 1996 to June 1997 and included 36,391 children, showed that vaccination coverage was up-to-date in 80 percent of children who received IPV as their first dose and in 80 percent of children who received OPV. Use of IPV as the first dose of polio vaccine increased from less than 2 percent of children born in 1996, to 15 percent of children born in the first three months of 1997, to 30 percent of those born in the second quarter of 1997. Nationwide, IPV use increased from 6 percent of all polio vaccine doses distributed in 1996 to 29 percent in 1997 and 34 percent in 1998. Through August 1999, as many as 69 percent of purchased doses of polio vaccine were IPV.
The currently available vaccines are more immunogenic than the original IPV introduced in 1955. Studies have shown that protective antibodies to all three types of poliovirus develop in 90 to 100 percent of children after two doses and in 99 to 100 percent of children after three doses. Although long-term data are not available, one study revealed that antibodies persisted for four years.
IPV Vaccination in Adults
While routine poliovirus vaccination is not required in adults in the United States, vaccination is recommended in five different circumstances: travelers to areas or countries where polio is epidemic or endemic; members of communities or specific population groups with disease caused by wild polioviruses; laboratory workers who handle specimens that might contain polioviruses; health care workers who have close contact with patients who might be excreting wild polioviruses; and unvaccinated adults whose children will be receiving OPV.
In unvaccinated adults, two doses of IPV should be administered at intervals of four to eight weeks and the third dose should be administered within six to 12 months of the second dose. When protection is needed before this period of time, alternatives include administration of three doses of IPV four weeks apart if more than eight weeks are available before protection is required. If less than eight weeks but more than four weeks are available, two doses of IPV should be administered at least four weeks apart. If fewer than four weeks are available before protection is needed, a single dose of IPV is recommended. One dose of IPV can also be administered to adults at increased risk who have had a primary series of OPV or IPV.