Israel was one of the first countries to administer mass vaccination. Consequently, it was among the first countries to experience significant breakthrough infections due to the waning of vaccine-induced immunity, which led to a resurgence of the epidemic. To mitigate the outbreak, Israel launched a pioneering booster campaign. Israels success in curtailing the Delta resurgence while imposing only mild non-pharmaceutical interventions has been instrumental in influencing the decision of many countries to initiate a booster campaign. By constructing a detailed mathematical model and calibrating it to the Israeli data, we expand our understanding of the impact of the booster campaign from the individual to the population level. We use the calibrated model to explore counterfactual scenarios in which the booster vaccination campaign is altered and to assess the direct and indirect effects in the different scenarios. Our results point to the vast benefits of vaccinating younger age groups that are not at a high risk of developing severe disease but play an important role in transmission. We further show that when the epidemic is exponentially growing the success of the booster campaign is highly sensitive to the timing of its initiation. Hence a rapid response is an important factor in reducing disease burden using booster vaccination.
Booster vaccination to curtail COVID-19 resurgence - population-level implications of the Israeli campaign