Israel Medical Association Journal

The Israel Ministry of Health’s epidemiology department reported a record number of 1564 new pertussis cases in 2004. This brings the incidence rate to 23 per 100,000 population, indicating a marked increase in the prevalence of pertussis, from 1–3/100,000 in 1998, 9 in 2001, to 14 in 2003. The rate of atypical pertussis presentations in vaccinated patients, the decline in pertussis immunity post-vaccination, and the decreased awareness of potential infections in the adult population make the diagnosis of pertussis difficult and contribute to the rising incidence. In this article we review the current literature in order to increase awareness of the occurrence of pertussis in children as well as adults, discuss the laboratory diagnostic methods being used, and report the currently recommended means of treating the disease.

Background: Pertussis is the only vaccine-preventable disease that has re-emerged in Israel. The reported crude incidence of the disease increased 16-fold since 1998.

Objectives: To describe the epidemiology of pertussis and to explain the substantial increase in reported pertussis incidence in Israel in recent years.

Methods: Crude and specific pertussis incidence by age, patient immunization status, hospitalization rate and national immunization coverage rate were calculated from information provided by the public health offices of the Ministry of Health.

Results: The reported crude incidence of pertussis increased from 1–2/100,000 in 1994–98 to 23/100,000 in 2004. The trend was observed in all age groups, being most prominent in infants under age 1 year and in children aged 5–14. The incidence of pertussis was substantially higher in unvaccinated and partly vaccinated compared to fully vaccinated persons. Fifteen percent of notified cases were hospitalized, but in infants under age 1 year the hospitalization rate was 50%. National pertussis immunization coverage by age 2 years was stable during the last 10 years.

Conclusions: There are several possible explanations for the re-emergence of pertussis in Israel. The most plausible reason seems to be the waning of vaccine-induced immunity in face of infrequent natural exposure to the infectious agent and lack of a pertussis vaccine booster dose after age 1.
 

Background: Poliovirus rapidly evolves by nucleic acid substitutions and genetic recombination with other polioviruses and non-polio enteroviruses. Evolving oral poliovirus (Sabin strains) can rapidly revert to neurovirulence and undergo antigenic alterations.

Objectives: To evaluate the threat of vaccine-derived poliovirus (1–15% divergence from the respective Sabin strain) for a poliomyelitis-free population in a country with a long-standing routine vaccination program.

Methods: We characterized genetic and antigenic changes in OPV[1] strains isolated from sewage in Israel and evaluated intestinal immunity by measuring fecal excretion after OPV challenge of vaccinated children.

Results: Characterization of poliovirus from sewage revealed eight type 2 and three type 3 vaccine polioviruses that had replicated and started to evolve (vaccine that replicated and diverged by 0.5 to ≤ 1.0%) and nine highly diverged type 2 vaccine-derived polioviruses (1–15% divergence from the respective Sabin strain) with 8–14% divergence between the years 1998 and 2005. Six of the eleven VRPV[2] uniquely recombined with OPV and/or NPEV[3]. The nine VDPV[4] were epidemically related, genotypically neurovirulent, and had 10–15 amino acid substitutions in antigenic sites altering their antigenicity, but shared a single recombination. Type 2 OPV was excreted by 23% and 17% of infants challenged with OPV 3 months after partial immunization (two doses each of OPV and enhanced inactivated poliovirus) or full immunization (three doses of each) respectively, despite high humoral antibody titers.

Conclusions: Our findings, which show that OPV is excreted for a significant period by children with high humoral immunity, emphasize the long-term potential threat from VDPV in highly vaccinated populations. An adequate immunization program, combined with environmental surveillance, is necessary to prevent poliomyelitis and community transmission of poliovirus. 

For children born after 1 January 2005, use of the Sabin oral polio vaccine in combination with the enhanced-potency Salk inactivated polio vaccine as part of the routine vaccination schedule was discontinued. The schedule now includes only IPV [1]. In September 2005, a fifth dose of pertussis vaccine was added for pupils in their second year of elementary school. This article describes the reasons for these changes, which have rendered Israel's routine vaccination program one of the most effective in the world.