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. 2024 May;18(5):e13307.
doi: 10.1111/irv.13307.

Seroprevalence of Protective Antibodies Against Influenza and the Reduction of the Influenza Incidence Rate: An Annual Repeated Cross-Sectional Study From 2014 to 2019

Raquel Guiomar  1 , Susana Pereira da Silva  2 , Inês Costa  1 , Patricia Conde  1 , Paula Cristóvão  1 , Ana Paula Rodrigues  2 , Aida Fernandes  3 , Ana Paula Dias  4 , Ana Rita Couto  5 , Angélica Ramos  6   7 , Carina Moita  8 , Carina Rodrigues  9 , Fátima Vale  8 , Filomena Caldeira  9 , Jácome Bruges Armas  5 , João Pereira-Vaz  10 , José Alves  11 , Ludivina Freitas  11 , Luis Martins  12 , Luís Milho  3 , Luisa Mota-Vieira  13 , Lurdes Lopes  14 , Margarida Freitas  15 , Maria Ana Pessanha  4 , Maria Correia  10 , Maria Helena Marques  16 , Maria João Cardoso  6 , Maria João Peres  17 , Mário Cunha  12 , Patricia Amantegui  18 , Paula Mota  15 , Paulo Lopes  19 , Paulo Pereira  16 , Regina Viseu  17 , Rita Cabral  13 , Rita Côrte-Real  14 , Sofia Almeida  18 , Vânia Soares  19 , Kamal Mansinho  4 , Olav Hungnes  20 , Baltazar Nunes  2
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Seroprevalence of Protective Antibodies Against Influenza and the Reduction of the Influenza Incidence Rate: An Annual Repeated Cross-Sectional Study From 2014 to 2019

Raquel Guiomar et al. Influenza Other Respir Viruses. 2024 May.

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.

Keywords: ILI incidence rate; antibodies; influenza; seroprevalence.

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Conflict of interest statement

The authors declare no conflicts of interest.

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