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Int J Infect Dis. 2014 Jan;18:81-3. doi: 10.1016/j.ijid.2013.09.015. Epub 2013 Oct 29.

Lack of herd immunity against measles in individuals aged <35 years could explain re-emergence of measles in Catalonia (Spain).

Author information

1
Public Health Agency of Catalonia, Department of Health of Catalonia, Bac de Roda 83-85, 08005 Barcelona, Spain; CIBER - Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain. Electronic address: pedro.plans@gencat.cat.
2
Public Health Agency of Catalonia, Department of Health of Catalonia, Bac de Roda 83-85, 08005 Barcelona, Spain; CIBER - Epidemiology and Public Health (CIBERESP), Instituto de Salud Carlos III, Madrid, Spain.
3
Public Health Agency of Catalonia, Department of Health of Catalonia, Bac de Roda 83-85, 08005 Barcelona, Spain.

Abstract

OBJECTIVES:

The objective of this study was to assess the association between lack of herd immunity in some population groups and the re-emergence of measles in Catalonia in 2006.

METHODS:

Herd immunity was considered established in the different population groups when the prevalence of positive serological results to measles was higher than the herd immunity threshold of 90%. The Chi-square test and the odds ratio were used to assess the association between lack of herd immunity and measles cases in the outbreak of 2006-2007.

RESULTS:

Herd immunity was not established against measles in individuals aged 0-14 years and 25-34 years, as the prevalence of positive serological results was <90% in these groups. In the measles outbreak of 2006-2007, 91% of cases occurred in age groups without herd immunity, and only 9% of cases occurred in age groups with herd immunity (p<0.001). The odds ratio for the association between lack of herd immunity and measles cases in the outbreak of 2006-2007 was 104 (p<0.001).

CONCLUSION:

Lack of herd immunity in individuals aged<35 years could be one of the factors underlying the re-emergence of measles in Catalonia.

KEYWORDS:

Herd immunity; Measles elimination; Measles outbreaks; Prevention; Seroepidemiology

PMID:
24211476
DOI:
10.1016/j.ijid.2013.09.015
[Indexed for MEDLINE]
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