Immunity to poliomyelitis in Sydney's children

Area of Science:

• Public Health
• Immunology
• Epidemiology

Background:

• No indigenous poliomyelitis cases in New South Wales since 1970 suggested high herd immunity.
• Previous assumptions of widespread polio immunity in children were questioned.

Purpose of the Study:

• To assess the serological immunity status of children in Sydney to poliovirus.
• To evaluate the effectiveness of a single Sabin vaccine dose in children with inadequate antibody levels.

Main Methods:

• A neutralization test survey was conducted on Sydney children to determine antibody levels against all three poliovirus serotypes.
• Children with inadequate antibody levels received a single dose of Sabin vaccine, and their post-vaccination antibody titers were assessed.

Main Results:

• Only 42% of surveyed children had adequate antibody levels to all three poliovirus serotypes; 12% had no demonstrable antibodies.
• Vaccination history was an unreliable indicator of immunity, with 48% of children reported to have received multiple doses lacking full immunity.
• A single Sabin vaccine dose in children with inadequate immunity resulted in 77% achieving adequate antibody levels to all three serotypes.

Conclusions:

• Significant gaps in poliovirus immunity exist among Sydney children, challenging assumptions of herd immunity.
• The Sabin vaccine is effective in rapidly boosting immunity in previously under-immunized children.
• The findings led to a mass immunization campaign and a review of the recommended pediatric immunization schedule in New South Wales.