ObjectiveTo investigate the immune level against seasonal influenza viruses in healthy adults in Beijing.

MethodsIn April 2017, the study subjects were randomly selected from communities in six districts in Beijing. A questionnaire survey was conducted among them and serum samples were collected from them to detect the antibodies against seasonal influenza viruses, including influenza A (H1N1) pdm09 virus, influenza A (H3N2) virus, influenza B virus Victoria lineage and influenza B virus Yamagata lineage. The positive rates of the antibodies and the genmetric mean titers (GMTs) in different groups were compared.

ResultsA total of 1 163 healthy adults were surveyed, in which 645 were positive for at least one antibody. The positive rates for A (H1N1) pdm09, A (H3N2), B Victoria lineage and B Yamagata lineage viruses were 25.62%, 44.88%, 1.98% and 3.53% respectively. The antibody against A (H3N2) virus had the highest GMT of 1∶24.75, while the GMT of antibody against B Victoria lineage virus was lowest (1∶5.67). The differences in antibody positive rate and GMT were significant among the four subtype influenza viruses (P＜0.001). The positive rates of antibodies against A (H3N2), B Victoria lineage and B Yamagata lineage viruses and the GMT of A (H3N2) virus antibody were higher in males than in females (P＜0.05). There were significant differences in positive rates of antibodies against A (H1N1) pdm09 virus and A (H3N2) virus and the GMTs among the populations from different districts (P＜0.05). Similar results were observed in different age groups for the positive rates of antibodies against A (H1N1) pdm09, A (H3N2) and B Yamagata lineage viruses (P＜0.001). The antibody level to A (H3N2) virus and GMT were highest in age group ≥60 years , while the antibody levels to A (H1N1) pdm09 virus and B Yamagata lineage virus and GMTs were highest in age group 18–29 years. The persons receiving vaccination in past year had higher positive rates of antibodies and GMTs against A (H1N1) pdm09, A (H3N2) and B Yamagata lineage viruses compared with unvaccinated persons (P＜0.05).

ConclusionThe positive rates of antibodies against B Victoria lineage and B Yamagata lineage viruses were low in healthy adults in Beijing, suggesting the high risks for outbreaks of infections of B Victoria lineage and B Yamagata lineage viruses. The factors influencing the antibody levels of different subtype influenza viruses slightly differed, and there was a correlation between vaccination or other factors and antibody positive rate.