Measles in Papua New Guinea: An age-specific serological survey
Introduction
Measles is a viral infection common in childhood. It may have severe complications with a mortality rate of up to 5–10% in developing countries. The introduction of a highly effective, low-cost live attenuated measles vaccine (measles-containing vaccine, MCV) 40 years ago has greatly reduced global measles incidence. However, measles remains one of the major contributors to the mortality of young children in low income countries, with an estimated 242,000 deaths per year in 2006 [1], [2]. High population immunization coverage is the mainstay of measles control, reducing ongoing transmission of virus and the risk of outbreaks. At least 95% of the population needs to be immune to avoid ongoing outbreaks [3]. To achieve this goal, the immunization coverage must be more than 90%. The World Health Organization (WHO) also recommends that a second opportunity for immunization should be available for all children. In its Strategic Plan 2001–2005, WHO names Papua New Guinea (PNG) as 1 of 47 priority countries for measles mortality reduction and regional elimination [4].
In the Western Pacific region, WHO has resolved to eliminate measles by 2012 [5]. Such a goal requires substantial resources to achieve and sustain high immunization coverage, a well organized and comprehensive surveillance system, and the capacity to confirm suspected cases by laboratory testing. These components are essential in order to control the disease, but are real challenges for countries such as PNG with low income and limited infrastructure. In non-outbreak situations, WHO recommends a first dose of MCV at 9 months of age, with a second opportunity for immunization at least 1 month after the first dose, ideally after the first year of life [3]. Additionally, “catch-up” Supplementary Immunization Activities (SIA) is proposed, in order to increase coverage and provide this second opportunity [5].
Measles immunization was introduced to PNG in 1982 using a modified two dose schedule at 6 and 9 months of age. This aimed to provide partial coverage for young infants who were at high risk of death, neurological sequelae [4], [6] or pneumonia. Nonetheless, the coverage across the country remained low, with the 2007 national coverage reported to be 58% for the first dose and 47% for the second dose [7]. Epidemic measles has been cycling through PNG since 1998 – there have been more than 30,000 cases reported, and an estimated several thousand deaths, many in young infants, and some in young adults [8]. An SIA campaign was conducted district by district over a period of 18 months, reaching Madang in late 2004.
Surveys performed in PNG in the past 20 years have demonstrated high mortality and morbidity rates in children younger than 9 months [8], and informed the decision to administer the first dose of MCV at 6 months of age. However, debate continues regarding the efficacy of this dose, as the sero-conversion rate is known to be only about 80–85% after immunization at 9 months and even lower in infants 6 months old [9]. Theoretically, sero-conversion is best achieved after 15 months (when it is >95%), but recent studies [10], [11] carried out in Africa have demonstrated the efficacy of immunization as early as 4.5 months old in an outbreak situation [10]. There is additional evidence to suggest that even if infection is not prevented, early immunization with MCV may increase protection against severe morbidity and death due to measles infection in infants less than 12 months of age [12].
Discussions around the age of immunization, as well as the unexpected age distribution of measles cases in recent outbreaks, support the need for better understanding of population immunity. To date, there have been no population-based serological surveys in PNG to estimate the proportion of the community with antibodies to measles. Age-specific immunity profiles describe the size and age distribution of the population vulnerable to infection and provide evidence for planning immunization campaigns and adapting the current Expanded Programme of Immunization (EPI) schedule.
In the present survey, we investigated the age-specific seroprevalence of measles antibody in a non-epidemic context by immunization status and location. We estimated the immunization coverage, identified the age groups and locations most at risk of measles outbreaks and related sero-protection to immunization history.
Section snippets
Design
We conducted a prospective cross-sectional survey in Madang province, Papua New Guinea. The two sites for the study were the outpatient clinic of Yagaum rural hospital, located about 20 km from Madang town and mainly serving a rural population, and the Jambo town clinic in Madang town, serving mainly poor and mobile communities from surrounding urban settlements. The protocol was approved by the Institute of Medical Research Institutional Review Board (28/08/2007, IMRIRB 0715) and the Medical
Results
Four hundred and fifty one patients were enrolled in the study from September 2007 to June 2008. Demographic data including crude odds ratios’ (OR) is summarized in Table 1. The detailed routine immunization coverage in children less than 10 years is summarized in Table 2. To allow comparison with national coverage surveys, we also calculated reported coverage with one or two doses of measles vaccine among children aged 12–23 months who had a verifiable date of birth. In this age group, the
Discussion
Dried blood samples have been extensively evaluated by the global measles/rubella laboratory network and have been shown to provide a reliable quantitative immunoglobulin titration [13].
This study highlighted very low measles immunization coverage in Madang province with a recorded coverage (with one or two doses) of 41% in children below 10 years, a level consistent with the national routine health information system. It correlates with a low proportion of immunity (77%) in the general
References (20)
- et al.
Serological and epidemiological effects and influence factors of primary immunization with current live attenuated measles vaccine (Hu191) among infants aged 6–15 months
Vaccine
(2001) - et al.
Unacceptably high mortality related to measles epidemics in Niger, Nigeria, and Chad
PLoS Med
(2007) Measles control and the prospect of eradication
Curr Top Microbiol Immunol
(2009)Measles vaccines
WER
(2004 April 14)The crisis of measles and the need to expand the ways of delivering vaccines in Papua New Guinea
PNG Med J
(2003)- WHO, Western Pacific regional plan of action for measles elimination who regional office for the Western Pacific...
- et al.
Molecular analysis of measles virus genome derived from SSPE and acute measles patients in Papua New Guinea
J Med Virol
(2002) - ...
- et al.
Control measures and outcome of the measles epidemic of 1999 in the eastern highlands province
PNG Med J
(2000) - et al.
Protective efficacy of standard Edmonston–Zagreb measles vaccination in infants aged 4.5 months: interim analysis of a randomised clinical trial
BMJ
(2008)
Cited by (11)
Waning immunity to measles in young adults and booster effects of revaccination in secondary school students
2013, VaccineCitation Excerpt :This seropositivity rate is similar to that reported in other eastern province of China [10], which may help to explain the recent high incidence rate of measles. Specifically, the lowest seropositivity rate was in infants 4–7 months of age (36%) in our study, that is why many measles cases occur in babies before eligible age for measles vaccination [11,12]. However, the debate continues regarding whether or not to advance the administration of first dose [13,14], because the first dose of MCV was administered at 8 months of age in China, and it is the earliest delivery in the world.
Rubella control in Papua New Guinea: Age-specific immunity informs strategies for introduction of rubella vaccine
2012, VaccineCitation Excerpt :The study was conducted between September 2007 and June 2008 [19], and examined the aetiologies of fever in participants. Sample size calculations, based on expected measles seroprevalence, suggested at least 50 participants per pre-defined age group (<1, 1–4, 5–9, 10–14, 15–24, >25 years) would be required to determine measles seroprevalence [20]. Written informed consent was obtained from participants or care-givers prior to data and sample collection.
Serological assessment of the establishment of herd immunity against measles in a health district in Malaysia
2016, BMC Infectious DiseasesSystematic Review of Measles and Rubella Serology Studies
2016, Risk Analysis