Influenza seroprotection correlates with predominant circulating viruses during 2014/15 and 2015/16 seasons in Portugal

Rede Portuguesa de Laboratórios para o Diagnóstico da GripeBACKGROUND: Population immune profile for influenza is highly affected by circulating influenza viruses, thus changing the risk of infection for influenza. This study aims to assess influenza immunity in the Portuguese population by age groups, during 2014 and 2015 and establish a relationship between seroprotection and circulating influenza viruses in 2014/15 and 2015/16 seasons. METHODS: Two cross-sectional studies were developed based on a convenience serum sample collected in June 2014 (n=626) and July 2015 (n=675) in hospitals from mainland and Azores and Madeira.Serums equally represent all age groups. Antibody titers were evaluated by HI assay for strains recommended for seasonal influenza vaccine northern hemisphere,2014/15 and 2015/2016. Seroprevalences were estimated for each strain by age group and the association with seasonal cumulative influenza-like illness (ILI) rates for influenza virus during both seasons was analised. RESULTS: In June 2014 the highest seroprotection was observed for influenza A(H3) (39.0%; 95% CI: 36.2-43.8%) and A(H1)pdm09 (29.7; 95% CI: 26.3-33.4%), with higher levels in children 5-14 years old. In 2014/2015 a dominant circulation of influenza B/Yamagata was observed with high incidence rates in individuals under 65 years old, the ones that had lower seroprotection. Although before the start of the season high protection for A(H3) was observed, the circulation of the new drift A(H3) strains had gained an immunological advantage,in accordance with A(H3) elevated incidence rates observed during 2014/15. In July 2015 the highest seroprotection was observed for influenza B/ Yamagata (55.1%; 95% CI: 51.4-58.9%), 2.4 times the estimated 2014.This increase was even more pronounced in younger (≤ 4 years old), 6.3 times increase in 2015.This fact is in agreement with the predominant influenza B virus detected and the high ILI incidence rate observed in children during 2014/2015 epidemic. Seroprotection levels for influenza A in July 2015 were not significantly different from 2014.During 2015/16 season, influenza A(H1N1)pdm09 was predominant, with high incidence rate in < 65 year old. Influenza B/Victoria lineage,although detected at low levels increased in frequency, in agreement with the lowest level of seroprotection detected in the general population before the start of 2015/2016 season (21.8%; 95% CI: 18.7-24.0%). CONCLUSIONS There was a correlation between virus circulation, incidence rates for each age group and the previous seroprotection for seasonal influenza viruses.Our study highlights the value of measuring the serological profile for influenza to establishe risk groups for infection for which an increase preventive measures, including vaccination, should be fostered.info:eu-repo/semantics/publishedVersio

Cross-protection to new drifted influenza A(H3) viruses and prevalence of protective antibodies to seasonal influenza, during 2014 in Portugal

Em colaboração com a Rede Portuguesa de Laboratóros para o Diagnóstico da GripeIntroduction: Immune profile for influenza viruses is highly changeable over time. Serological studies can assess the prevalence of influenza, estimate the risk of infection, highlight asymptomatic infection rate and can also provide data on vaccine coverage. The aims of the study were to evaluate pre-existing cross-protection against influenza A(H3) drift viruses and to assess influenza immunity in the Portuguese population. Materials and methods: We developed a cross-sectional study based on a convenience sample of 626 sera collected during June 2014, covering all age groups, both gender and all administrative health regions of Portugal. Sera antibody titers for seasonal and new A(H3) drift influenza virus were evaluated by hemagglutination inhibition assay (HI). Seroprevalence to each seasonal influenza vaccine strain virus and to the new A(H3) drift circulating strain was estimated by age group, gender and region and compared with seasonal influenza-like illness (ILI) incidence rates before and after the study period. Results: Our findings suggest that seroprevalences of influenza A(H3) (39.9%; 95% CI: 36.2–43.8) and A(H1)pdm09 (29.7%; 95% CI: 26.3–33.4) antibodies were higher than for influenza B, in line with high ILI incidence rates for A(H3) followed by A(H1)pdm09, during 2013/2014 season. Low pre-existing crossprotection against new A(H3) drift viruses were observed in A(H3) seropositive individuals (46%). Both against influenza A(H1)pdm09 and A(H3) seroprotection was highest in younger than 14-years old. Protective antibodies against influenza B were highest in those older than 65 years old, especially for B/Yamagata lineage, 33.3% (95% CI: 25.7–41.9). Women showed a high seroprevalence to influenza, although without statistical significance, when compared to men. A significant decreasing trend in seroprotection from north to south regions of Portugal mainland was observed. Conclusions: Our results emphasize that low seroprotection increases the risk of influenza infection in the following winter season. Seroepidemiological studies can inform policy makers on the need for vaccination and additional preventive measures.This work was supported by the National Institute of Health Doutor Ricardo Jorge, IP Lisbon, Portugal.info:eu-repo/semantics/acceptedVersio

Núcleos de Ensino da Unesp: artigos 2008

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq