Transmission dynamic of influenza B virus Yamagata lineage and assessment of infection control measures in schools in Shenzhen

ObjectiveTo analyze transmission dynamic of influenza B virus Yamagata lineage and assess the effects of vaccination and isolation measures for the outbreaks in schools in Shenzhen, 2017.

MethodsThe susceptible-exposed-infectious/asymptomatic-removed (SEIAR) model was used to simulate the data from field investigation. Then the basic reproduction number (R₀) was calculated to evaluate the infectious ability of the virus. The SEIARV (vaccination) and SEIARQ (isolation) models were developed, then the cumulative incidence rate (TAR) and the duration of outbreak (DO) were calculated to evaluate the effectiveness of vaccination and isolation measures.

ResultsAt the end of 2017, the R₀ of the B/Y influenza outbreak in Shenzhen was 5.97 (95% CI: 3.66−8.28); the epidemic would last for 52 days without any intervention and the TAR would be 99.57%. In the context of vaccination with inactivated influenza vaccine (IIV) before outbreak, when the vaccination rate was 30%, 50% and 70%, the TAR after vaccinations with IIV3 or IIV4 would be 80.51%/76.81%, 65.07%/58.48%, and 44.06%/33.77%. In the context of the emergent vaccination after outbreak, when the vaccination rate was 30%, 50%, and 70%, the TAR after vaccination with IIV3 or IIV4 was 85.94%/82.46%, 73.55%/67.03% and 57.90%/47.54%. In the context of combined intervention of vaccination and isolation before outbreak, when the vaccination rate is ≥50%, the TAR would be ＜1%. In the context of combined intervention of emergent vaccination and isolation after outbreak, when the vaccination rate is ≥50%, the TAR would be ＜5%.

ConclusionInfluenza B virus Yamagata-lineage has a strong ability to spread in school outbreaks. In the context of vaccination with IIV3 or IIV4, high coverage combined with isolation is an effective prevention and control measure.