The timing of polio immunization doses to optimize protection of U.S. children against importation or outbreaks is a central feature of a new Policy Statement from the American Academy of Pediatrics.
"The policy is intended to clarify the optimal interval of dosing for polio vaccine and the need for a booster dose at 4 to 6 years old regardless of the timing of prior doses," Dr. Michael E. Pichichero said in an interview. "The timing of a booster dose to provide sustained protection over time and avoid early waning of immunity is key."
The American Academy of Pediatrics (AAP) recommends a four-dose, standard schedule for administration of inactivated poliovirus vaccine (IPV) to U.S. children. The statement recommends doses at 2 months, 4 months, at 6 months through 18 months, and again at 4 years through 6 years of age.
The timing and spacing of doses is important. The minimum age for the first dose is 6 weeks. In addition, the minimum interval should be 4 weeks between doses one and two and between doses two and three. The final, booster dose should be administered at least 6 months after the preceding dose.
"Clinicians should know that a dose should be provided to the child between 4 and 6 years even if there were four doses given before that time," said Dr. Mary Ann Jackson, one of the 13 members of the American Academy of Pediatrics (AAP) Committee of Infectious Diseases that wrote the policy statement (Pediatrics 2011;128:805-8).
"The optimal dosing schedule is scientifically based and reflects our knowledge that wider spacing of doses is associated with stronger immune responses," said Dr. Pichichero, a clinical professor of pediatrics and infectious diseases at the University of Rochester (N.Y.) Medical Center. He was not involved in writing the policy statement.
In contrast, use of minimum dosing intervals is recommended for babies at imminent risk of exposure to circulating polioviruses through travel to a country where polio is endemic or through an outbreak. The policy statement reads: "Although not ideal, the greater majority of infants vaccinated at the minimum age with minimum intervals are protected from polio, and with imminent risk of exposure, the benefits of using the abbreviated schedule far outweigh any risks of failure to induce a protective immune response."
"The timing of a [polio] booster dose to provide sustained protection over time and avoid early waning of immunity is key."
"Circulation of polio in the United States stopped several decades ago, and there was hope that global eradication was imminent. However, polio cases continue to occur in countries around the world," said Dr. Jackson, chief, Section of Infectious Diseases at Children’s Mercy Hospitals and Clinics, Kansas City, Mo.
"The updated polio policy from the AAP is important to emphasize the routine schedule and to alert families to the risk of exposure to polio related to international travel."
"The recent spread of polio from Pakistan to China – a country which had been polio-free for 10 years – is a sign of how important it is to remain vigilant with respect to polio immunization," Dr. Jackson said. To date, reported cases in China include six children under age 3 years and four young adults, with one death. "The country has taken a very strong stand and plans to immunize more than 8 million people over several weeks – a daunting task."
In addition to Pakistan, pockets of endemic poliovirus remain in India, Afghanistan, and Nigeria. These four countries never interrupted indigenous transmission of the virus and exported the poliovirus to 19 other countries that reported cases in 2009. The number of cases of wild poliovirus infections worldwide decreased from 1,604 in 2009 to 1,304 in 2010, but the number of countries reporting polio cases last year increased to 20. Chad, the Democratic Republic of the Congo, Angola, and Sudan, for example, have known or suspected re-establishment of disease.
"Many of the children who are travelers to at risk countries are going with their parents to visit relatives. These families may be less likely to seek specific travel medicine clinic referral but generally most have a medical home that provides immunization," Dr. Jackson said. "This makes the pediatric providers’ role in providing appropriate vaccines in addition to providing other travel counseling especially important."
The committee recommends widespread use of IPV to maintain high levels of polio immunity in the U.S. population given risk for importation of pathogenic polioviruses. Individual protection is important, they added, because if polio is introduced, pockets of under-immunized children in the country might sustain transmission of the virus.