Background: Moldova experienced a nationwide mumps outbreak between 2007 and 2008. Single-dose monovalent mumps vaccination at 15 to 18 months was introduced in 1983, replaced by a 2-dose MMR schedule at age 1 and 6 to 7 years in 2002. We investigated the outbreak to quantify its extent, explore the role of primary and secondary vaccine failure, and provide control recommendations.
Methods: We analyzed national mumps surveillance and vaccination coverage data to estimate vaccine effectiveness (VE) using the screening method. A retrospective cohort study in 5 educational institutions was conducted to determine age-specific attack rates (ARs) and VE. We compared vaccine strain-specific ARs. Isolation and genotyping of mumps virus strains were performed.
Results: Of 31,142 cases reported during October 2007 and July 2008, 80% were in 15- to 24-year-olds. Of cases with information (66%), 92% were vaccinated once, 4% twice. One-dose mumps VE estimates based on surveillance data over 1997–2001 declined from 91% (95% CI: 88%–92%) in 2-year-olds to 72% (70%–74%) in 15- to 19-year-olds. In the cohort study (n = 1589), VE was −40% (−120% to 20%) for 1 dose. For 2 doses it was 62% (−43% to 90%) in 13- to 15-year-olds. ARs were higher in individuals vaccinated with Urabe strains (43%) than with Leningrad-Zagreb strains (14%, P < 0.001). Mumps virus genotype G5 was identified.
Conclusions: Low effectiveness of single-dose mumps vaccination was the main cause of the outbreak. Waning immunity may have contributed to this. The risk of mumps in 2-dose vaccinees was low. Other countries in which large population groups have received <2 doses of mumps vaccine may face similar outbreaks.
From the *Institut de Veille Sanitaire (InVS), Départment des Maladies Infectieuses, Paris, France; †European Programme for Intervention Epidemiology Training (EPIET), Stockholm, Sweden; ‡Bernhard Nocht Institute for Tropical Medicine (BNI), Infectious Disease Epidemiology Group, Hamburg, Germany; §Robert Koch Institute (RKI), Department for Infectious Disease Epidemiology, Berlin, Germany; ¶Postgraduate Training for Applied Epidemiology (PAE), Berlin, Germany; ∥Seconded to Bavarian Health and Food Safety Authority (LGL), Department of Health and Nutrition, Oberschleissheim, Germany; **National Scientific and Applied Centre for Preventive Medicine, Department of General Epidemiology, Chisinau, Moldova; ††Health Protection Agency (HPA), Centre for Infections, London, United Kingdom; ‡‡World Health Organization (WHO), Country Office of the Russian Federation, Vaccine Preventable Diseases and Immunization Programme, Moscow, Russia; §§World Health Organization (WHO), Regional Office for Europe, Copenhagen, Denmark; and ¶¶National Institute for Public Health and the Environment (RIVM), Centre for Infectious Disease Control, Bilthoven, The Netherlands.
Accepted for publication January 28, 2010.
N.G.S. and H.B. both are first authors.
Address for correspondence: Helen Bernard, MD, Department for Infectious Disease Epidemiology, Robert Koch Institute, DGZ-Ring 1, 13086 Berlin, Germany. E-mail: BernardH@rki.de.
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