Current measles outbreaks: can we do better for infants at risk?

Estimating the measles effective reproduction number in Australia from routine notification data

OBJECTIVE

To estimate the measles effective reproduction number (R) in Australia by modelling routinely collected notification data.

METHODS

R was estimated for 2009-2011 by means of three methods, using data from Australia's National Notifiable Disease Surveillance System. Method 1 estimated R as 1 - P, where P equals the proportion of cases that were imported, as determined from data on place of acquisition. The other methods estimated R by fitting a subcritical branching process that modelled the spread of an infection with a given R to the observed distributions of outbreak sizes (method 2) and generations of spread (method 3). Stata version 12 was used for method 2 and Matlab version R2012 was used for method 3. For all methods, calculation of 95% confidence intervals (CIs) was performed using a normal approximation based on estimated standard errors.

FINDINGS

During 2009-2011, 367 notifiable measles cases occurred in Australia (mean annual rate: 5.5 cases per million population). Data were 100% complete for importation status but 77% complete for outbreak reference number. R was estimated as < 1 for all years and data types, with values of 0.65 (95% CI: 0.60-0.70) obtained by method 1, 0.64 (95% CI: 0.56-0.72) by method 2 and 0.47 (95% CI: 0.38-0.57) by method 3.

CONCLUSION

The fact that consistent estimates of R were obtained from all three methods enhances confidence in the validity of these methods for determining R.

Spatiotemporal analysis of infant measles using population attributable risk in Shandong province, 1999-2008

BACKGROUND

Reduction of measles incidence and mortality has been encouraging in China. However, it remains an important public health concern among infants. This study aimed to examine the space-time distribution pattern of infant measles occurrence for the period of 1999-2008 in Shandong, China.

METHODS AND FINDINGS

Measles cases among infants aged younger than 1 year were obtained from the national infectious diseases reporting information system. A spatiotemporal analysis using population attributable risk percent (PAR%) was used to distinguish between multiple geographic clusters of potential interest. The analysis detected 29 statistically significant space-time clusters with the most likely cluster in Zaozhuang City from 2006 to 2008. Of the 28 secondary clusters, 22 were found in 2008. The map of PAR%, relative risk (RR) and space-time cluster analysis indicated that the clusters were generally unchanged, and were found south-west and north-west of Shandong. The Lanshan District in Linyi had the highest PAR%, while highest RR was in the Yicheng District in Zaozhuang.

CONCLUSION

There were significant space-time clusters of infant measles in Shandong over the study period. PAR% is an effective way to analyze multiple clusters from their application like RR. Interrupting measles circulation and maintaining routine coverage over 95% may be the only effective strategy to achieve measles elimination.

Effect of in-utero HIV exposure and antiretroviral treatment strategies on measles susceptibility and immunogenicity of measles vaccine

INTRODUCTION

The high burden of maternal HIV-infection in sub-Saharan Africa may affect measles control. We evaluated the effect of in-utero HIV-exposure and antiretroviral treatment (ART) strategies on measles antibody kinetics prior and following measles vaccination.

METHODS

Infants aged 6-12 weeks were enrolled. This included HIV-uninfected infants born to HIV-uninfected (HUU) and HIV-infected mothers (HEU). Additionally, we enrolled perinatal HIV-infected infants with CD4% equal or greater than 25% randomized to deferred-ART until clinically or immunologically indicated (Group-3) or immediate-ART initiation (Group-4). Group-4 was further randomized to interrupt ART at 1 year (Group-4a) or 2 years of age (Group-4b). Additionally, a convenience sample of HIV-infected infants with CD4⁺ less than 25% initiated on immediate-ART was enrolled (Group-5). Measles immunoglobulin-G antibodies were quantified by an indirect enzyme immunoassay with titers 330 mIU/ml or more considered 'sero-protective'. The referent group was HUU-children.

RESULTS

The proportion with sero-protective titers at 7.3 weeks of age was higher in HUU (65.2%) compared with any HIV-infected group (range: 16.7-41.8%), but dropped to less than 17% in all groups at age 19.6 weeks. Twenty-eight weeks following the first measles vaccine, Group-4a was less likely to have sero-protective titers (79.3%) as compared to HUU (91.1%; P<0.0001), Group-3 (95.7%; P=0.003) or Group-4b (92.1%; P=0.018). Although the proportion with sero-protective levels were similar between groups immediately postbooster dose, this was lower in HEU (79.6%; P=0.002) and Group-4a (80.3%; P=0.010) compared with HUU (94.3%) 41-weeks later.

CONCLUSION

Greater waning of immunity among HIV-infected children in whom ART was interrupted and in HEU following a booster-dose, indicate the possible need for further measles-booster doses after 2 years of age in these children.

Progress in the elimination of measles and congenital rubella in Central Italy

Despite the launch of a WHO European Region strategic plan 2005-2010 for eliminating measles and rubella and preventing congenital rubella (CR) infection, measles and rubella are still circulating in Europe. Increased transmission and outbreaks of measles in Europe were still observed in 2011. In Italy, the objectives of the National Plan (2003-2007) for measles elimination have not yet been achieved. The goal of measles elimination and incidence reduction of CR cases has been postponed to 2015 by the Italian Ministry of Health through the implementation of the new National Plan 2010-2015 which will require (1) the achievement of more than 95% coverage with 1 dose and two doses of measles containing vaccine (MCV), respectively, within 24 mo and within 12 y of age; (2) supplementary vaccination activities aimed at susceptible populations including adolescents, young adults and those at risk (health care and educational workers, military, groups "hard to reach" like nomads); and in addition, (3) reduction to less than 5% in the proportion of susceptible women of childbearing age (especially immigrant women). Experiences at regional level, like in Tuscany, have shown promising results in order to create an integrated surveillance system between regional and local health authorities, university and laboratory and in the future, to validate elimination. Moreover, the evaluation of all preventive activities performed in Tuscany during the last decade, immunization coverage data, sero-epidemiological population profile and incidence of measles and rubella cases has highlighted critical points which should be improved and good practices already implemented which should be maintained in the future in order to reach the new goals.

Measles outbreak in Europe: susceptibility of infants too young to be immunized

As women vaccinated against measles transfer low amounts of antibodies, an increasing number of infants lack early protection through maternal antibodies until being immunised themselves. This paper reviews the literature on disease burden of measles in the population too young to be immunized according to the respective national recommendations during recent outbreaks in EU and EEA/EFTA countries. In addition, specific control strategies adopted to protect this young population are reviewed. Pubmed, Unbound Medline, Web of Knowledge and the Eurosurveillance database were searched using MESH terms: measles and epidemiology, measles and infants, prevalence of measles, measles and outbreaks and measles and epidemic. Additionally, data from Euvac.net and ECDC were consulted. Databases were searched from January 2001 to September 2011. Fifty-three papers were included in the analysis. The percentage of all measles cases during outbreaks affecting young infants ranged from 0.25% to 83.0%. Specific control strategies were adopted: e.g. administration of the first or second vaccine dose earlier than recommended. Infants younger than 12 months are often involved in measles outbreaks, and advancing the first vaccine dose could reduce the burden of disease. However, immunization before 9 months of age is not systematically recommended because of dysmature humoral immune responses of infants. High coverage and timely administration of the recommended series of vaccines are the most important measures to decrease measles incidence and measles circulation and protect vulnerable infants from infection.