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Measles susceptibility in a large urban center in Northeast Brazil and its implications for viral reintroduction risk

Maria Eduarda Maia Vilar1, Florisneide Rodrigues Barreto2, Ramon da Costa Saavedra2,3

  • 1Institute of Collective Health, Federal University of Bahia, Salvador, BA, Brazil. vilar.eduarda@gmail.com.

BMC Public Health
|July 15, 2026
PubMed
Abstract

Insights

Measles IgG antibody levels are declining in young adults in Brazil, indicating immunity gaps. This decline, despite high overall seroprevalence, may increase susceptibility to measles outbreaks in urban areas.

Area of Science:

  • Immunology
  • Epidemiology
  • Public Health

Background:

  • Declining measles-specific IgG antibodies in vaccinated individuals may not reflect protective immunity.
  • Changes in population-level serological profiles impact understanding of measles susceptibility.
  • This study addresses shifts in measles antibody distribution in Salvador, Brazil.

Purpose of the Study:

  • To analyze changes in the age distribution of measles-specific IgG antibodies.
  • To assess population susceptibility to measles in Salvador, Brazil, between 2000 and 2024.
  • To identify factors associated with measles seropositivity.

Main Methods:

  • Population-based seroprevalence study with a household-based cluster sampling design.
  • Included 1,508 individuals, comparing data to a 2000 survey.
  • Measured measles-specific IgG antibodies using ELISA and collected sociodemographic and vaccination data.

Main Results:

  • Overall measles IgG seroprevalence was 82.4%, below the threshold for transmission interruption.
  • The 20-29-year age group showed the most significant decline in seropositivity (95.7% to 60.4%).
  • Previous measles infection was the only factor positively associated with seropositivity.

Conclusions:

  • Despite high overall seroprevalence, immunity gaps exist, particularly in young adults.
  • These gaps may facilitate measles outbreaks in large urban centers.
  • Findings highlight the need for continued monitoring of population immunity.
Keywords:
ImmunityImmunoglobulin GMeaslesMeasles-mumps-rubella vaccineSeroepidemiologic studiesUrban populationVaccination

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