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Abstract：
BACKGROUND: Seroepidemiological studies provide estimates of population-level immunity, prevalence/incidence of infections, and evaluation of vaccination programs. We assessed the seroprevalence of protective antibodies against influenza and evaluated the correlation of seroprevalence with the cumulative annual influenza incidence rate.
METHODS: We conducted an annual repeated cross-sectional seroepidemiological survey, during June-August, from 2014 to 2019, in Portugal. A total of 4326 sera from all age groups, sex, and regions was tested by hemagglutination inhibition assay. Seroprevalence and geometric mean titers (GMT) of protective antibodies against influenza were assessed by age group, sex, and vaccine status (65+ years old). The association between summer annual seroprevalence and the difference of influenza incidence rates between one season and the previous one was measured by Pearson correlation coefficient (r).
RESULTS: Significant differences in seroprevalence of protective antibodies against influenza were observed in the population. Higher seroprevalence and GMT for A(H1N1)pdm09 and A(H3N2) were observed in children (5-14); influenza B seroprevalence in adults 65+ was 1.6-4.4 times than in children (0-4). Vaccinated participants (65+) showed significant higher seroprevalence/GMT for influenza. A strong negative and significant correlation was found between seroprevalence and ILI incidence rate for A(H1N1)pdm09 in children between 5 and 14 (r = -0.84; 95% CI, -0.98 to -0.07); a weak negative correlation was observed for A(H3N2) and B/Yamagata (r ≤ -0.1).
CONCLUSIONS: The study provides new insight into the anti-influenza antibodies seroprevalence measured in summer on the ILI incidence rate in the next season and the need for adjusted preventive health care measures to prevent influenza infection and transmission.
METHODS: We conducted an annual repeated cross-sectional seroepidemiological survey, during June-August, from 2014 to 2019, in Portugal. A total of 4326 sera from all age groups, sex, and regions was tested by hemagglutination inhibition assay. Seroprevalence and geometric mean titers (GMT) of protective antibodies against influenza were assessed by age group, sex, and vaccine status (65+ years old). The association between summer annual seroprevalence and the difference of influenza incidence rates between one season and the previous one was measured by Pearson correlation coefficient (r).
RESULTS: Significant differences in seroprevalence of protective antibodies against influenza were observed in the population. Higher seroprevalence and GMT for A(H1N1)pdm09 and A(H3N2) were observed in children (5-14); influenza B seroprevalence in adults 65+ was 1.6-4.4 times than in children (0-4). Vaccinated participants (65+) showed significant higher seroprevalence/GMT for influenza. A strong negative and significant correlation was found between seroprevalence and ILI incidence rate for A(H1N1)pdm09 in children between 5 and 14 (r = -0.84; 95% CI, -0.98 to -0.07); a weak negative correlation was observed for A(H3N2) and B/Yamagata (r ≤ -0.1).
CONCLUSIONS: The study provides new insight into the anti-influenza antibodies seroprevalence measured in summer on the ILI incidence rate in the next season and the need for adjusted preventive health care measures to prevent influenza infection and transmission.
摘要：
背景：血清流行病学研究提供了对人群免疫水平的估计，感染率/发病率，和疫苗接种计划的评估。我们评估了针对流感的保护性抗体的血清阳性率，并评估了血清阳性率与累积年度流感发病率的相关性。
方法：我们进行了每年重复的横断面血清流行病学调查，6月-8月,从2014年到2019年，在葡萄牙。所有年龄组共有4326份血清，性别,和区域通过血凝抑制试验进行测试。按年龄组评估抗流感保护性抗体的血清阳性率和几何平均滴度（GMT），性别,和疫苗状态（65岁以上）。通过皮尔逊相关系数（r）测量夏季年度血清阳性率与一个季节与前一个季节之间流感发病率差异之间的关联。
结果：在人群中观察到针对流感的保护性抗体的血清阳性率存在显著差异。在儿童（5-14）中观察到A（H1N1）pdm09和A（H3N2）的血清阳性率和GMT更高；65岁以上的成人乙型流感血清阳性率是儿童（0-4）的1.6-4.4倍。接种疫苗的参与者（65岁以上）对流感的血清阳性率/GMT显着升高。在5至14岁的儿童中，A（H1N1）pdm09的血清阳性率与ILI发生率之间存在强烈的负相关和显着相关（r=-0.84；95％CI，-0.98至-0.07）；A（H3N2）和B/山形（r≤-0.1）观察到弱负相关。
结论：该研究为夏季测量的抗流感抗体血清阳性率对下一季ILI发病率的影响提供了新的见解，以及需要调整预防性保健措施来预防流感感染和传播。
方法：我们进行了每年重复的横断面血清流行病学调查，6月-8月,从2014年到2019年，在葡萄牙。所有年龄组共有4326份血清，性别,和区域通过血凝抑制试验进行测试。按年龄组评估抗流感保护性抗体的血清阳性率和几何平均滴度（GMT），性别,和疫苗状态（65岁以上）。通过皮尔逊相关系数（r）测量夏季年度血清阳性率与一个季节与前一个季节之间流感发病率差异之间的关联。
结果：在人群中观察到针对流感的保护性抗体的血清阳性率存在显著差异。在儿童（5-14）中观察到A（H1N1）pdm09和A（H3N2）的血清阳性率和GMT更高；65岁以上的成人乙型流感血清阳性率是儿童（0-4）的1.6-4.4倍。接种疫苗的参与者（65岁以上）对流感的血清阳性率/GMT显着升高。在5至14岁的儿童中，A（H1N1）pdm09的血清阳性率与ILI发生率之间存在强烈的负相关和显着相关（r=-0.84；95％CI，-0.98至-0.07）；A（H3N2）和B/山形（r≤-0.1）观察到弱负相关。
结论：该研究为夏季测量的抗流感抗体血清阳性率对下一季ILI发病率的影响提供了新的见解，以及需要调整预防性保健措施来预防流感感染和传播。
