SIMID | Simulation Models of Infectious Disease

Technical note: SARS-CoV-2 variants and vaccination in Belgium (v2022-08-31)

The SIMID consortium prepared a new technical note (v2022-08-31) containing the estimates of a stochastic dynamic transmission model using observational data up to August 23rd, 2022.

The full document from August 2022 (v2022-08-31) is available here.

Study highlights:

  • We explored the potential impact of and increasing transmission in September 2022 as a result of resuming societal activities and seasonality. In addition we explore the potential impact of a vaccination campaign starting on September 12, 2022 in different target groups.
  • Our scenario analysis shows a new wave in October-November as a result of resuming societal activities and seasonality. However, a booster vaccine campaign with an Omicron dedicated booster and coverage of at least 50% of the oldest population (65 years and older) with already one booster shows a substantial impact on the size thereof. More specifically, including vaccination in the scenario analysis results in a wave moderate in size, near the level of the latest Omicron wave in June. Projections with subsequent vaccination campaign targeting the 18 years and older population show the lowest hospital admission rates in December 2022. While we focus on hospital admissions, high infection rates could lead to significant absenteeism and pressure on primary care.
  • While the timing and height of the project peaks are subject to our model assumptions, the main value of this work lies in the relative comparison between different strategies and the overall risk assessment.
  • A growing body of evidence shows that individuals who have been infected and/or vaccinated (with or without a booster) lose their protection over time. This implies that infections and therefore hospital admissions could reach a long-term equilibrium, of which the level depends on the waning rates. An equilibrium can be disturbed when a change in contacts and/or transmission dynamics occurs due to (non-)pharmaceutical interventions or seasonality.
  • We are making the implicit assumption that Omicron BA.5 will remain dominant throughout the entire simulation period. Nonetheless, other (newly emerging) VOCs may have different transmission probabilities and different probabilities to cause disease, hospitalization or death, and different vaccine effectiveness characteristics against each of these manifestations.

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