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Clin Infect Dis. 2019 May 6. pii: ciz363. doi: 10.1093/cid/ciz363. [Epub ahead of print]

Emergence of attenuated measles illness among IgG positive/IgM negative measles cases, Victoria​, Australia 2008-2017.

Author information

1
Health Protection Branch, Victorian Department of Health and Human Services, Australia.
2
The Peter Doherty Institute for Infection and Immunity, the University of Melbourne and the Royal Melbourne Hospital​, Victoria, Australia.
3
Department of Infectious Diseases, Alfred Hospital, Victoria, Australia.
4
Victorian Infectious Diseases Reference Laboratory, Royal Melbourne Hospital, at the Peter Doherty Institute for Infection and Immunity, Victoria, Australia.
5
Department of Epidemiology and Preventive Medicine, School of Public Health and Preventive Medicine, Monash University, Victoria, Australia.
6
Department of Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
7
Department of Infectious Diseases, National University Hospital, Singapore.

Abstract

BACKGROUND:

Waning measles immunity among vaccinated individuals may result in an attenuated illness and is considered less infectious. This study aims to compare the epidemiological, clinical, and laboratory profile of measles cases with waning immunity to other measles cases.

METHODS:

PCR-positive (+) measles cases notified to Victoria's Department of Health and Human Services (DHHS) from 2008-2017 with immunoglobulin (Ig)M and IgG tested at diagnosis were classified according to serology at diagnosis: IgG negative (-) [non-immune]; IgM+/IgG+ [indeterminate]; or IgM-/IgG+ [waning immunity].

RESULTS:

Between 2008-2017, 297 measles cases were notified of whom 190 (64%) were included in this analysis; 151/190 (80%) were non-immune at diagnosis, 26 (4%) were indeterminate and 13 (7%) had waning immunity. Between 2008-13 and 2014-17, the proportion of cases with waning immunity increased from 0/87 (0%) to 13/103 (13%) (p<0.001) and the diagnostic sensitivity of initial IgM fell from 93% to 81% (p=0.012), respectively. Seven (54%) waning immunity cases reported receiving measles-containing vaccines; one case had two documented doses and three cases had one documented dose. Compared to non-immune and indeterminate cases, waning immunity cases were more likely to be male; less likely to report fever, coryza, and cough; and had lower burden of virus (higher Ct values on respiratory specimens). Among IgG+ cases, waning immunity cases had higher IgG titres than indeterminate cases (mean optical density [OD] values 1.96 vs. 0.71, p=0.004). Onward transmission from one waning immunity case to two infant household contacts too young for vaccination was documented.

CONCLUSIONS:

Waning immunity among measles cases (IgM-/IgG+ at diagnosis), associated with secondary vaccine failure and modified clinical illness, is emerging in Victoria with transmission potential.

KEYWORDS:

immunity; measles elimination; measles vaccine; secondary vaccine failure; measles

PMID:
31056637
DOI:
10.1093/cid/ciz363

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