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Decrease in overdispersed secondary transmission of COVID-19 over time in Japan

Takeshi Miyama1,2, Sung-Mok Jung2,3, Hiroshi Nishiura2

  • 1Osaka Institute of Public Health, Osaka, Japan.

Epidemiology and Infection
|November 15, 2022
PubMed

Insights

COVID-19 transmission became less variable over time, with the Alpha variant showing reduced offspring distribution dispersion. This shift may decrease the effectiveness of targeted interventions for controlling severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Area of Science:

  • Epidemiology
  • Infectious disease dynamics
  • Public health

Background:

  • Coronavirus disease 2019 (COVID-19) initially showed overdispersed transmission, suggesting targeted interventions could be effective.
  • Emerging variants of concern with increased transmissibility complicate control efforts.
  • Understanding temporal changes in COVID-19 transmission patterns is crucial for effective public health strategies.

Purpose of the Study:

  • To investigate and quantify temporal variations in the offspring distribution dispersibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
  • To compare transmission patterns during periods dominated by the ancestral variant versus the Alpha variant (B.1.1.7).

Main Methods:

  • Analysis of contact tracing data from Nagano, Japan.
  • Fitting a negative binomial distribution to empirically observed offspring distributions.
  • Estimation of the dispersion parameter (k) for different COVID-19 waves.

Main Results:

  • The offspring distribution was less dispersed during the Alpha variant wave (wave 4, k = 0.32) compared to the ancestral variant wave (wave 2, k = 0.21).
  • Household transmission constituted a high proportion during wave 4.
  • The proportion of transmissions generating over five secondary cases remained consistent across the studied periods.

Conclusions:

  • COVID-19 transmission became less dispersed with the emergence of the Alpha variant.
  • Reduced transmission variability may diminish the effectiveness of interventions focused on high-risk groups or settings.
  • Continued monitoring of transmission dynamics is essential for adapting public health responses to evolving SARS-CoV-2 variants.

Keywords:
Heterogeneitymathematical modelsevere acute respiratory syndrome 2 (SARS-CoV-2)super-spreading eventtransmissibilitytransmission dynamics

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