How Many Children in American Samoa Have Had Dengue? A 2023 School Survey

This report describes the dengue vaccine recommendation in force in 2023–2024. Check CDC's current guidance on dengue vaccination.

Dengue is caused by four dengue viruses and spread by the bite of infected Aedes mosquitoes. In American Samoa, where transmission is classed as frequent or continuous — more than 10 cases in at least 3 of the previous 10 years — 660 confirmed cases were reported to CDC during the 2016–2018 outbreak.

Why past infection matters for vaccination

An infection usually gives lifelong immunity to the virus type that caused it, but only temporary protection against the other three. A second dengue infection is more likely to cause severe illness than a first or later one — severe dengue meaning plasma leakage leading to shock or fluid build-up with breathing difficulty, severe bleeding, or severe organ damage.

In 2021, CDC's Advisory Committee on Immunization Practices recommended the Dengvaxia vaccine for people aged 9–16 with laboratory-confirmed previous dengue infection who live in areas of frequent or continuous transmission. In trials, it protected people who had had dengue before, but vaccinated people who had never been infected faced a higher risk of severe dengue and hospitalisation.

Most dengue infections cause no symptoms or only mild ones and are rarely confirmed in a laboratory, so eligibility depends on a positive result from a blood test meeting CDC's performance standards. In places where few people have had dengue, those tests are more likely to give false positives. To avoid vaccinating children wrongly identified as previously infected, the vaccine is introduced only where at least 20% of eligible children and adolescents have had dengue. At that level, a test with at least 75% sensitivity and 98% specificity has a positive predictive value of at least 90%.

No one knew how many children in American Samoa had had dengue.

The survey

On August 8, 2023, the American Samoa Department of Health asked CDC to help measure previous dengue infection among school-age children through a school-based survey. Seven of the territory's 36 public schools — five elementary and two high schools — were chosen at random, stratified by school type, and all students in grades 3–10 there were invited. Those with signed parental permission were tested with a rapid dengue immunoglobulin G test (sensitivity 89.6%, specificity 95.7%). Estimates were weighted for the survey design and adjusted for the test's accuracy. The test was used for public health purposes only, not to decide whether individual children could be vaccinated; that requires a two-test process in a laboratory certified for clinical results, which American Samoa did not have at the time.

What it found

In September–October 2023, 2,267 students were invited and 887 (39%) were tested. Their median age was 11 (range 7–16), and 54% were female.

• 492 (56%) tested positive for dengue antibodies, 371 (42%) tested negative, and 24 (3%) had results that could not be read.
• Estimated seroprevalence was 61% among girls and 56% among boys.
• Across all students aged 7–16 it was 59%; among those aged 9–16, the ages eligible for vaccination, it was 60%.
• It was lowest among 8-year-olds, at 46%.

What it means

At about 60%, previous dengue infection among eligible children in American Samoa is far above the 20% threshold for introducing the vaccine — the level set to reduce severe dengue and hospitalisation while limiting the risk of vaccinating children who have never been infected. High levels in every age group also point to widespread past exposure, and so to the risk of future outbreaks and of the second infections that are more often severe.

The authors suggest that in American Samoa, dengue vaccination could be one part of a wider strategy that also includes mosquito control around homes, protection from mosquito bites, training health care providers to recognise and treat dengue, and stronger laboratory capacity for surveillance.

Sources

Based on "Notes from the Field: Prevalence of Previous Dengue Virus Infection Among Children and Adolescents Aged 7–16 Years — American Samoa, September–October 2023," by Sandra Kiplagat and colleagues (CDC; American Samoa Department of Health; Pacific Island Health Officers Association), Morbidity and Mortality Weekly Report 73(31), published by the Centers for Disease Control and Prevention; rewritten in hubnx's own words.