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Adult vaccine failure leads to measles outbreak in Micronesia
A 2014 measles outbreak affecting 393 people in the Federated States of Micronesia may be the result of vaccine failure and improper administration, according to recent research in MMWR.
“Although measles is typically a childhood disease, outbreaks affecting all age groups have occurred, particularly in populations too small to sustain endemic transmission,” the researchers wrote. “However, in this outbreak, the extent of transmission among adults with documented receipt of MMR vaccine, including many with two doses, is atypical.”
On Feb. 16, 2014, patients with fever and rash were evaluated at Kosrae State Hospital and initially diagnosed with dengue fever or chikungunya. Serum samples positive for measles-specific immunoglobulin M antibodies were first reported on May 15, with subsequent diagnoses made using WHO guidelines.
From mid-February to the end of August, there were 139 measles cases detected in the state of Kosrae, 251 detected in Pohnpei, and three detected in Chuuk. Of these cases, 36% were laboratory confirmed, 62% were epidemiologically confirmed, and 2% were clinically compatible. Sixty-four percent of the patients (median age, 24 years) were aged older than 19 years. Just under one-third of patients required hospitalization, and the only death was a Pohnpei boy aged 21 months.
Vaccination records were available for 306 patients. Seventy-one percent of these patients had received at least one measles-containing vaccine (MCV) dose before the outbreak, while 70% of adults with vaccination records had received two or more doses of MCV. Among unvaccinated patients, 3% were adults, 33% were children and adolescents aged 1 to 19 years, and 60% were infants aged younger than 1 year.
After measles cases were identified, a mass vaccination campaign was conducted in each of the country’s four states for those without two documented doses of MCV. In addition, vaccine storage equipment and handling practices were reviewed at Kosrae Public Health Clinic. Multiple inadequacies in vaccine management and documentation were identified, the researchers wrote, and may have led to suboptimal protection among adults vaccinated decades earlier.
“Vaccine failure can result from improper vaccine storage and handling, leading to decreased vaccine potency,” the researchers wrote. “[Federated States of Micronesia] is a tropical country with multiple vaccine storage challenged, including high ambient temperatures, frequent power outages and inter-island shipping issues.
“Few measles cases in children aged younger than 9 years were identified, and most of these occurred in unvaccinated children, which suggests recent cold chain practices were adequate. Historical cold chain lapses are the most plausible explanation for prevalent vaccine failure seen in adults in this outbreak.” – by Dave Muoio
Disclosure: The researchers report no relevant financial disclosures.