Pertussis: herd immunity and vaccination coverage in St Lucia

Area of Science:

• Epidemiology
• Infectious Disease Dynamics
• Vaccinology

Background:

• Pertussis (whooping cough) poses a public health challenge, particularly in populations with varying vaccination rates.
• Understanding disease transmission dynamics is crucial for effective control strategies.
• The role of subclinical infections in maintaining endemic disease in vaccinated populations requires further investigation.

Purpose of the Study:

• To compare pertussis case rates across communities with different vaccination coverages.
• To assess the relationship between vaccination coverage and herd immunity.
• To evaluate the theory of endemic subclinical pertussis maintaining transmission.

Main Methods:

• Analysis of pertussis case data during a complete epidemic on the island of St Lucia.
• Comparison of disease incidence in small communities with varying child vaccination coverage.
• Population dynamics modeling to assess transmission theories.

Main Results:

• A clear association was observed between higher vaccination coverage and increased herd immunity.
• Individual protection from vaccination was imperfect, yet community-level immunity was significant.
• Population dynamics analysis refuted the theory of endemic subclinical pertussis driving transmission in highly vaccinated groups.

Conclusions:

• Achieving 80% homogeneous vaccination coverage in 2-year-old children could lead to pertussis eradication on the island.
• This scenario presents a practicable public health experiment for disease elimination.
• Herd immunity plays a critical role in controlling pertussis outbreaks, even with imperfect individual vaccine efficacy.