2002至2019年臺灣麻疹病例年齡－世代－年代分析及突破性感染者臨床表徵

Epidemiological And Clinical Characteristics of Measles Cases in Taiwan: An Age–Period–Cohort Analysis, 2002–2019

麻疹被視為極具根除潛能之疫苗可控制疾病，但自2018年起，陸續有高收入且具完整疫苗接種計畫國家發生疫情，感染者有趨向年輕成人趨勢。
本研究以回溯性世代研究方式，將2002至2019年臺灣本國籍麻疹確定病例（397例）分為3個疫苗政策介入世代，包含(1) Cohort A：1976年8月以前出生者（未受惠疫苗接種計畫）；(2) Cohort B：1976年9月至1990年9月出生（幼年應接種2劑MV疫苗及1劑MMR疫苗）；及(3) Cohort C：1990年10月以後出生（幼年至少應接種2劑MMR疫苗），分析麻疹病例年齡、世代及年代變化，及突破性感染者臨床與實驗室檢驗特徵。
近18年臺灣本國籍麻疹確定病例，有46.6%為Cohort B出生世代，其中18至39歲占44.8%。另檢視136名18至39歲於2018至2019年確診者，有83名(61%)急性期血清抗體檢驗為IgM(-)/IgG(+)，其中2名感染者經流行病學調查證實造成疫情擴散；72名(53%)無咳嗽、流鼻水／鼻炎及結膜炎等任一種症狀。原發性感染者與疫苗接種失敗感染者，於臨床症狀及急性期血清抗體表現具統計差異，但仍可由核酸(RT-PCR)檢驗證實感染。
臺灣與其他高疫苗接種率／低疾病發生率國家相似，近年均觀察到成人麻疹突破性感染，本研究進行麻疹病例年齡-世代-年代分析，可標記出高感染風險者，進一步為臺灣成人麻疹疫苗接種對象與時程提供建議。

Measles is regarded as a disease that can be fully eradicated and controlled by vaccination. However, measles outbreaks have been observed since 2018 in high-income countries with complete measles vaccination programs, and the infection of measles in young adults is increasing.
A retrospective cohort study was conducted by dividing Taiwanese patients diagnosed with measles between 2002 and 2019 into three groups according to the different vaccination policy periods. Specifically, (1) Cohort A: born before August 1976 (no mass immunization); (2) Cohort B: born between September 1976 and September 1990 (when infants were recommended to receive 2 doses of MV plus 1 dose of MMR); and (3) Cohort C: born after October 1990 (when infants are recommended to receive at least 2 doses of MMR). Analysis was conducted to explore the age of onset, differences between the cohorts, changes in the incidence rates across different periods, and the clinical symptoms and laboratory characteristics of patients with breakthrough infection.
Among the confirmed measles cases in Taiwan over the past 18 years, 46.6% belonged to Cohort B. Among the 136 patients aged 18–39 years who were diagnosed with measles between 2018 and 2019, 83(61%) were IgM (-)/IgG (+) in acute-phase sera, 2 patients caused an outbreak. Moreover, 72 (53%) cases did not present cough, coryza, or conjunctivitis. Statistical significances were observed between patients with primary infection and those with failed vaccination in the clinical symptoms and acute phase serum antibody results. The RT-PCR tests proved enable to verify the measles infections accurately.
Similar to other countries with high vaccination rates and low measles incidence, adults with breakthrough infections have been seen in Taiwan in recent years. In this study, we performed analysis on the age–period–cohort allowed to identify individuals with high risks of measles infection and provide suggestions on determining vaccination targets and schedules.