Measles Outbreak and Response --- Fiji, February--May 2006

In September 2005, the 37 countries and areas of the World Health Organization (WHO) Western Pacific Region (WPR) established a goal to eliminate measles in the region by 2012. After multiple outbreaks in 1996 and 1997, measles supplementary immunization activities (SIAs) in 1997 and 1998 resulted in apparent interruption of measles transmission in WPR. Since then, importations have resulted in limited outbreaks in French Polynesia and Guam, a large outbreak in the Marshall Islands in 2003, and an outbreak in Fiji during February--May 2006. This report describes the epidemiologic findings, public health response, and potential causes of the 2006 outbreak that produced 132 measles cases in Fiji (2006 estimated population: 832,432), the most populous country in the South Pacific.

Background

To achieve and sustain measles elimination and prevent importation-associated outbreaks, the WPR office of WHO recommends that countries achieve and maintain vaccination coverage of >95% with 2 doses of measles vaccine in every district. The WPR office further recommends that countries ensure measles surveillance that 1) detects one or more suspected measles cases per 100,000 population per year in >80% of districts, 2) tests serum samples from >80% of persons with suspected measles, and 3) obtains a viral isolate from every chain of measles transmission (1).

Fiji's Expanded Program on Immunization introduced measles vaccine in 1982 as a single dose for children aged 9 months. From 1982 to 1998, reported routine measles vaccination coverage increased from 20% to 80%. Measles SIAs were conducted in 1998, targeting children aged 9 months--14 years and achieving an administrative vaccination coverage rate* of 85%, and in 2001, targeting children aged 9 months--5 years and achieving an administrative coverage of 86%.

In 2003, Fiji introduced a 2-dose schedule for measles-rubella vaccine, with doses administered at ages 1 year and 6 years, the latter at school entry. An SIA with measles-rubella vaccine targeting children aged 6--11 years was conducted during 2003--2004; administrative vaccination coverage was not reported. During 2001--2004, routine vaccination coverage with 1 dose of measles-rubella vaccine averaged 83% annually. Findings from a 2005 survey of children aged 12--23 months indicated nationwide vaccination coverage of 80% with 1 dose of measles-rubella vaccine, although pockets of lower coverage were identified.

Before 2006, the last laboratory-confirmed measles outbreak in Fiji occurred during September 1997--April 1998, when 955 measles cases were reported, of which 86% were in children aged <15 years. Since late 1998, Fiji had been considered measles-free. Isolated clinical measles cases had been reported, and rubella, but not measles, had been confirmed by laboratory testing.

Outbreak

On February 17, 2006, the Ministry of Health (MOH) in Fiji received a report of three infants, with rash onsets on February 8 and 11, who had been admitted to a divisional hospital because of suspected measles and pneumonia. The three infants lived near the international airport at Nadi in the Western Division. On February 23, measles was confirmed by serologic testing for the presence of anti-measles virus immunoglobulin M (IgM) at the national laboratory in Fiji and verified on February 28 by the WHO Measles Regional Reference Laboratory at the Victorian Infectious Diseases Reference Laboratory in Australia, where an isolate was identified as measles genotype H1.

During February 17--June 9, a total of 132 suspected measles cases were reported to MOH, including 22 that were laboratory confirmed (anti-measles virus IgM positive) (Figure). Among the 132 measles patients, 119 (90%) resided in the Western Division and 13 (10%) in the Central and Eastern divisions. Within the Western Division, one subdivision had 58 (44%) of the measles cases. Routine vaccination coverage with 1 dose of measles-rubella vaccine in this subdivision had been reported as 49% in 2004 and 68% in 2005. A total of 76 (58%) patients were aged <5 years; the highest incidence (378 cases per 100,000 population) was among children aged 6--11 months (Table). Thirty-one (23%) patients required hospitalization; no deaths were reported. For 41 children aged 12--59 months for whom MOH could obtain detailed case investigation data, 12 (29%) had received 1 dose of measles-rubella vaccine, 10 (24%) had not been vaccinated, and 19 (46%) had unknown vaccination status. As of August 8, no additional laboratory-confirmed measles cases had been reported with rash onset after May 21.

Outbreak Control Measures

Enhanced surveillance. Reporting of acute fever and rash cases was intensified in Fiji's 21-hospital sentinel surveillance network, initially created for acute flaccid paralysis surveillance as part of the global poliomyelitis eradication initiative. Daily telephone calls were made to all sentinel hospitals for reports on new patients. Illnesses with rash and fever were confirmed as measles if they met the WHO measles clinical case definition.^† To encourage case reporting, the national coordinator of the Expanded Program on Immunization provided daily surveillance summaries by e-mail and fax to all hospitals, selected health centers, and partner agencies.

Case management. Triage and measles treatment recommendations, based on WHO Integrated Management of Childhood Illnesses guidelines (2), were distributed to all health facilities and health workers to ensure that suspected measles cases were managed appropriately and to prevent measles virus transmission in health-care facilities. Vitamin A, a key part of WHO case-management guidelines to reduce measles morbidity and mortality, was distributed in capsules to all hospitals and health centers in late March.

Social mobilization. A multiphase social mobilization and communication plan was developed using WHO's Communication-for-Behavioral-Impact approach (3), to prompt individual and family action. The initial phase, "Beware," informed the public about the measles outbreak and promoted reporting of suspected cases. The second phase, "Vaccinate," promoted an immunization campaign, prompting parents and guardians to bring children in the targeted age group to vaccination sites made visible by large banners. Activities included distribution of 60,000 fact sheets to schools and community and religious organizations, announcements on television and radio, and advertisements in cinemas and newspapers.

Outbreak-response immunization (ORI). To protect children in the age groups accounting for >60% of cases and most at risk for severe outcomes, 91,595 children aged 6 months to <6 years were targeted with measles-rubella vaccine during March 20--May 3, 2006. A goal of >95% vaccination coverage was set for all administrative levels. Plans at the subdivisional level were developed for budget estimates and distribution of bundled vaccine and injection-safety items.^§ Campaign training workshops, including classes on vaccination safety, were conducted for health-care workers throughout the country. Vaccination-coverage rates with measles- rubella vaccine were reported twice weekly from all vaccination sites to promptly identify areas needing external assistance. Rapid vaccination-coverage monitoring, using a 20-household convenience sample format, was conducted in urban and other areas at risk for measles. If two or more homes contained unvaccinated children, the area was targeted for repeat vaccinations. Of 32 areas surveyed, 12 (38%) required follow-up.

MOH subsequently reported that 89,747 (98%) of targeted children had received measles-rubella vaccine as of May 24. Among 20 Fijian subdivisions, two had reported coverage <95%: Suva (91%) in the Central Division and Macuata (90%) in the Northern Division. No serious adverse events from vaccination were reported.

Reported by: S Samuela, T Tuiketei, Ministry of Health, Fiji. R Duncan, T Kubo, J Kool, K Chen, South Pacific Office; E Smith, M Hercules, Y Baoping, Western Pacific Regional Office; Vaccines and Biologicals Dept, WHO, Geneva, Switzerland. Global Immunization Div, National Center for Immunization and Respiratory Diseases (proposed), CDC.

Editorial Note:

The measles outbreak in Fiji described in this report, like the 2003 outbreak in the Marshall Islands, underscores that absence of measles virus transmission should not create a false sense of security and that high population immunity is essential to preventing future outbreaks (4). As an island, Fiji's isolation from countries where measles is endemic, combined with its small population, likely contributed to the lack of reported measles cases from late 1998 through 2005 (5,6). Low routine vaccination coverage, combined with persistent pockets of susceptible adolescents and adults despite previous SIAs and outbreaks, might have left the country vulnerable to an outbreak via importation.

Achieving >95% population immunity (i.e., through high vaccination coverage with 2 doses of measles vaccine) will halt measles transmission within a population (7). In Fiji, the high incidence of measles in a single subdivision with historically low routine measles vaccination coverage and the occurrence of measles in all age groups highlight the importance of monitoring measles vaccination coverage at subnational levels and in older age groups (i.e., aged >15 years) to ensure that pockets of measles susceptibility do not develop.

The first identified cases of measles in this outbreak were in children already hospitalized with pneumonia. Because recognition of measles might decrease after measles virus transmission has been interrupted for long periods, national programs should remind clinicians to be vigilant and to report suspected cases, particularly in areas of low vaccination coverage. To increase sensitivity and timeliness of surveillance, primary-care facilities and outpatient departments might be included as reporting sites, and community-based informants used to report suspected measles cases.

The findings in this report are subject to at least three limitations. First, surveillance was conducted through sentinel site reporting and, as a result, all suspected measles cases might not have been reported. Second, not all suspected measles cases were laboratory confirmed; therefore, some suspected cases might have had etiologies other than measles. Finally, the estimated vaccination coverage achieved in the ORI was based on administrative data. Because uncertainties often exist regarding the denominator used to calculate administrative coverage, these data generally are less reliable than survey-based coverage estimates.

Targeting children aged 6 months to <6 years during the ORI was important because this group accounted for >60% of cases and was more vulnerable to severe measles outcomes. The Fijian MOH rapidly achieved high vaccination coverage with measles vaccine. At the same time, a sharp decrease in reported cases among all age groups occurred. The effectiveness of the ORI is greater when the intervention occurs early in the course of an outbreak (8). In Fiji, the campaign began 6 weeks after the first case was reported; 8 weeks later, the last case was reported. The commitment by MOH and its partners to reach >95% of targeted children was essential to interrupting measles virus transmission and preventing spread of the measles virus to other vulnerable Pacific Islands.

References

1. World Health Organization, Regional Office for the Western Pacific. Field guidelines for measles elimination. Geneva, Switzerland: World Health Organization; 2004. Available at http://www.wpro.who.int.
2. Integrated management of childhood illnesses: IMCI planning guide: gaining experience with the IMCI strategy in a country. Geneva, Switzerland: World Health Organization; 1999. Available at http://www.who.int/child-adolescent-health.
3. World Health Organization, Mediterranean Centre for Vulnerability Reduction (WMC), Tunis, Tunisia. Mobilising for healthy behaviour. Geneva, Switzerland: World Health Organization; 2003. Available at http://wmc.who.int/strategic/mobilising/index.html.
4. Hyde TB, Dayan G, Langidrik JR, et al. Measles outbreak in the Republic of the Marshall Islands, 2003. Int J Epidemiol 2006;35: 299--306.
5. Rhodes CJ, Butler AR, Anderson RM. Epidemiology of communicable diseases in small populations. J Mol Med 1998;76:111--6.
6. Black FL. Measles endemicity in insular populations: critical community size and its evolutionary implications. J Theor Biol 1966;11:207--11.
7. Gay NJ. The theory of measles elimination: implications for the design of elimination strategies. J Infect Dis 2004;189(Suppl 1):S27--35.
8. Guris D, Auerbach SB, Vitek C, et al. Measles outbreaks in Micronesia, 1991 to 1994. Pediatr Infect Dis J 1998;17:33--9.

^* Calculated by dividing the number of doses of vaccine reported administered through the immunization campaign by the number of persons in the target population.

^† Fever with rash and at least one of the following: cough, coryza, or conjunctivitis.

^§ Bundling of vaccine, diluent, auto-disable syringes, vaccine-reconstitution syringes, and safety boxes.

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Date last reviewed: 9/7/2006