Polio; Mass Vaccination Better Than Routine Vaccination Source: Vaccine Weekly

Oral polio vaccine (OPV) is better when taken with company. Lots of company. Comparison of OPV immunogenicity after multiple routine childhood vaccinations and after mass vaccination campaigns in Jordan showed that OPV is more effective when administered en masse. The findings suggest that adding further doses of OPV to the routine schedule is unlikely to have as great an impact on the immune state of children as administering the same number of doses during mass campaigns," wrote U.S. Centers for Disease Control and Prevention (CDC) researcher Mary R. Reichler and colleagues in a special supplement of the Journal of Infectious Diseases dedicated to the Global Poliomyelitis Eradication Initiative ("Increased Immunogenicity of Oral Poliovirus Vaccine Administered in Mass Vaccination Campaigns Compared with the Routine Vaccination Program in Jordan," J Infect Dis, 1997;175(Suppl 1):S198-204).

  Although they represent a crucial component of the World Health Organization (WHO) strategy to eliminate polio from the planet, massive vaccination campaigns are more expensive than routine OPV administration. For this reason, several nations in which polio is endemic have yet to implement mass vaccinations, usually given during National Immunization Days (NIDs). Reichler et al. studied 254 Jordanian children who had received one to five OPV doses. They obtained serum samples before and after two subnational mass OPV vaccination campaigns (January 29 to February 19, 1994 and March 12 to April 3, 1994). A striking finding ... is the relatively low level of serologic immunity to poliovirus infection, especially to type 3, among children in the Jordan Valley after as many as five routine doses of OPV," Reichler et al. reported.

Regardless of the number of previous routine OPV doses they had received, children had high rates of seroconversion to all three types of poliovirus after receiving the vaccine during the mass vaccinations. Implementing mass vaccination campaigns may be an important means of boosting poliovirus type-specific immunity in populations with suboptimal immunity following routine vaccination, Reichler et al. concluded. A previous study conducted in Morocco yielded similar data (Richardson et al., Bull World Health Org, 1995;73:769-77).

  These findings are not merely of technical interest: there have been several polio outbreaks in populations with relatively high routine OPV coverage. The effectiveness of mass vaccination campaigns in raising poliovirus type- specific immunity demonstrated in the present study suggests a role for conducting these campaigns not just in polio-endemic countries but also in tropical and subtropical countries for a period of time following the apparent elimination of polio, thus reducing the risk of outbreaks if reintroduction of wild poliovirus occurs," Reichler et al. suggested. It is not clear why the mass vaccination was so much more effective than routine vaccination. The subjects in the Reichler et al. study received the same vaccine during routine vaccination as they did during the mass vaccinations. Subject age was the same for both means of OPV administration, making it unlikely that the findings were due to differences in maternal antibody, breast feeding, or age-related immune responsiveness.

  Maintenance of the cold chain could have been better during the relatively brief period of the mass vaccination campaign, but visits to 10 Jordanian vaccine-storage facilities during the investigation of a 1991 outbreak discovered no problems. Reichler et al. noted that secondary spread of vaccine virus to non- recipients has been documented during mass OPV vaccinations. They suggested that the study children may similarly have received multiple exposures to the vaccine virus: first as a vaccinee and later as a contact. The corresponding author for this study is Mary R. Reichler, Mailstop E-05, NIP, CDC, 1600 Clifton Rd., Atlanta, Georgia 30333.