The potential impact of expanding target age groups for polio immunization campaigns

BACKGROUND: Global efforts to eradicate wild polioviruses (WPVs) continue to face challenges due to uninterrupted endemic WPV transmission in three countries and importation-related outbreaks into previously polio-free countries. We explore the potential role of including older children and adults in supplemental immunization activities (SIAs) to more rapidly increase population immunity and prevent or stop transmission. METHODS: We use a differential equation-based dynamic poliovirus transmission model to analyze the epidemiological impact and vaccine resource implications of expanding target age groups in SIAs. We explore the use of older age groups in SIAs for three situations: alternative responses to the 2010 outbreak in Tajikistan, retrospective examination of elimination in two high-risk states in northern India, and prospective and retrospective strategies to accelerate elimination in endemic northwestern Nigeria. Our model recognizes the ability of individuals with waned mucosal immunity (i.e., immunity from a historical live poliovirus infection) to become re-infected and contribute to transmission to a limited extent. RESULTS: SIAs involving expanded age groups reduce overall caseloads, decrease transmission, and generally lead to a small reduction in the time to achieve WPV elimination. Analysis of preventive expanded age group SIAs in Tajikistan or prior to type-specific surges in incidence in high-risk areas of India and Nigeria showed the greatest potential benefits of expanded age groups. Analysis of expanded age group SIAs in outbreak situations or to accelerate the interruption of endemic transmission showed relatively less benefit, largely due to the circulation of WPV reaching individuals sooner or more effectively than the SIAs. The India and Nigeria results depend strongly on how well SIAs involving expanded age groups reach relatively isolated subpopulations that sustain clusters of susceptible children, which we assume play a key role in persistent endemic WPV transmission in these areas. CONCLUSIONS: This study suggests the need to carefully consider the epidemiological situation in the context of decisions to use expanded age group SIAs. Subpopulations of susceptible individuals may independently sustain transmission, which will reduce the overall benefits associated with using expanded age group SIAs to increase population immunity to a sufficiently high level to stop transmission and reduce the incidence of paralytic cases

Individual-Based Modeling Of Potential Poliovirus Transmission In Connected Religious Communities In North America With Low Uptake Of Vaccination

Background: Pockets of undervaccinated individuals continue to raise concerns about their potential to sustain epidemic transmission of vaccine-preventable diseases. Prior importations of live polioviruses (LPVs) into Amish communities in North America led to their recognition as a potential and identifiable linked network of undervaccinated individuals

Fatal respiratory disease due to Corynebacterium diphtheriae: case report and review of guidelines for management, investigation, and control

Dramatic reductions in the incidence of diphtheria and high levels of childhood vaccination in recent decades have led the United States to establish the goal of diphtheria elimination among persons < or = 25 years of age by the year 2000. In 1990, an unimmunized 25-month-old child died of respiratory diphtheria in Dade County, Florida, before treatment with diphtheria antitoxin could be instituted. Twenty-three asymptomatic household contacts and other close contacts of the child were identified, cultured for Corynebacterium diphtheriae, given antimicrobial prophylaxis, and vaccinated with diphtheria toxoid when indicated. Three contacts (13%) had pharyngeal cultures positive for toxigenic C. diphtheriae of the same type as that causing infection in the deceased child, but no additional cases developed. Although the source of infection was not determined, three other close contacts had recently been to Haiti, where diphtheria is endemic. A serological survey of 396 children < 5 years of age who received care at a medical center in Dade County revealed that 22% lacked protective immunity to diphtheria. Attainment of the goal of diphtheria elimination among persons < or = 25 years of age--and ultimately among all persons--will depend on the maintenance of a high level of clinical awareness of the disease, the prompt institution of preventive measures among close contacts of patients with sporadic cases, and improved vaccination levels among infants, children, and adults

Disease eradication as a public health strategy: a case study of poliomyelitis eradication.

Disease eradication as a public health strategy was discussed at international meetings in 1997 and 1998. In this article, the ongoing poliomyelitis eradication initiative is examined using the criteria for evaluating candidate diseases for eradication proposed at these meetings, which covered costs and benefits, biological determinants of eradicability (technical feasibility) and societal and political considerations (operational feasibility). The benefits of poliomyelitis eradication are shown to include a substantial investment in health services delivery, the elimination of a major cause of disability, and far-reaching intangible effects, such as establishment of a "culture of prevention". The costs are found to be financial and finite, despite some disturbances to the delivery of other health services. The "technical" feasibility of poliomyelitis eradication is seen in the absence of a non-human reservoir and the presence of both an effective intervention and delivery strategy (oral poliovirus vaccine and national immunization days) and a sensitive and specific diagnostic tool (viral culture of specimens from acute flaccid paralysis cases). The certification of poliomyelitis eradication in the Americas in 1994 and interruption of endemic transmission in the Western Pacific since March 1997 confirm the operational feasibility of this goal. When the humanitarian, economic and consequent benefits of this initiative are measured against the costs, a strong argument is made for eradication as a valuable disease control strategy