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Two independent outbreaks of measles in partially vaccinated junior high schools in Tottori, Japan
A Kawamoto1, T Honda, K Ishida
1Tottori Prefectural Public Health Laboratory, Japan.
Abstract:
We analyzed retrospectively a relative risk of measles attacks in vaccinated vs. unvaccinated students using two independent outbreaks in Japan. The first involved 33/328 (10%) students where 64% students and 30% measles cases had been vaccinated. The second involved 27/241 (11%) students where 81% students and 48% measles cases had been vaccinated. The attack rates of vaccinated vs. unvaccinated students were significantly low (p < 0.001), but they accounted 25% in both episodes. The statistically significant clinical features among vaccinated and unvaccinated cases included the average duration of fever, 5.16 +/- 1.71 vs. 6.67 +/- 2.19 days (p = 0.01) and the incidence of complications, 0 vs. 25%, respectively. These results suggested that the measles in vaccinated cases were mostly due to secondary failures.
Insights
Measles vaccination significantly reduces attack rates, but secondary vaccine failures can still occur. Vaccinated individuals experienced shorter fever duration and fewer complications, indicating vaccine effectiveness.
Area of Science:
- Epidemiology
- Immunology
- Public Health
Background:
- Measles outbreaks continue to pose a public health challenge.
- Vaccine effectiveness is crucial in controlling measles transmission.
Purpose of the Study:
- To evaluate the relative risk of measles attacks in vaccinated versus unvaccinated students.
- To analyze clinical features and complication rates in vaccinated and unvaccinated measles cases.
Main Methods:
- Retrospective analysis of two independent measles outbreaks in Japan.
- Comparison of attack rates, fever duration, and complication incidence between vaccinated and unvaccinated student groups.
Main Results:
- Vaccinated students exhibited significantly lower measles attack rates (p < 0.001).
- Vaccinated cases had a shorter average fever duration (5.16 days vs. 6.67 days) and no complications, versus 25% in unvaccinated cases.
- Despite reduced risk, vaccinated individuals accounted for 25% of cases in both outbreaks, suggesting secondary vaccine failures.
Conclusions:
- Measles vaccination is highly effective in reducing disease incidence and severity.
- Secondary vaccine failures are a notable factor in measles cases among vaccinated individuals.
- Further research into the mechanisms of secondary vaccine failure is warranted to optimize measles control strategies.