The SIMID consortium prepared a new technical note (v2023-08-24) containing the estimates of a stochastic dynamic transmission model focusing on the potential impact of the vaccination campaign starting in September 2023 in Belgium.

Study highlights

  • We explore the potential impact of a vaccination campaign starting on September 15, 2023 with an XBB.1.5 bivalent booster and with different theoretical uptakes, in addition to the potential impact of increased transmission from September 2023 onward as a result of resuming societal activities after the summer break and seasonality effects (e.g., as a result of a shift from outdoor to indoor contacts).

  • Our scenario analysis shows a considerable benefit from the vaccination campaign during November–December 2023. Regarding a possible wave in September–October due to the restart of activities, the benefit increases with an earlier start of the vaccination campaign. The benefit of a campaign targeting the same audience as the flu vaccine is almost double the benefit of a campaign targeting half of that audience. An additional 15% increase in vaccinated people has limited impact.

  • Modification of contact rates and seasonality is simulated in the future according to last years collected data and estimated parameters in order to reproduce potential changes in transmission. Therefore, the timing and height of the projected peaks are subject to the model assumptions and are not intended to be predictive. The main value of this work lies in the relative comparison between different strategies and the overall risk assessment.

  • We make the implicit assumption that Omicron XBB.1.5 and the close variants currently circulating will remain dominant throughout the simulation period. Nonetheless, other (newly emerging) VOCs may have different transmission probabilities and different probabilities of causing disease, hospitalization, or death, and different vaccine effectiveness characteristics against each of these manifestations. In particular, the still unknown particularities of the very recent EG.5 variant are not taken into account.

The full document from August 2023 (v2023-08-24) is available here.