In a recent study, researchers assess the implications of the coronavirus disease 2019 (COVID-19) booster vaccine on the Israeli population.
In June 2021, the Israeli population experienced a remarkable increase in COVID-19 breakthrough cases. During this period, almost 80% of the vaccine-eligible population was vaccinated with two doses of the BNT162b2 vaccine. This prompted the need to approve the administration of a booster vaccine in Israel.
Study
In the present study, researchers analyze the population-level effect of different aspects of the booster vaccine campaign on COVID-19 disease outcomes in Israel.
The fourth wave of COVID-19 in Israel occurred between July 1, 2021, to November 25, 2021. The team developed a discrete-time age-of-infection age-stratified transmission model that took the primary and booster vaccination into consideration, while also accounting for waning vaccine immunity over time. The model was calibrated and validated using nationwide data including the number of infections, disease severity, and vaccinations reported. All data were stratified according to age, vaccination status, and daily resolutions.
Demographic data collected for each individual included their age, residential area, dates of polymerase chain reaction (PCR) tests, dates of the first, second and third vaccinations, COVID-19-related hospitalizations, and deaths. The study included all PCR-positive severe COVID-19 cases from the fourth wave in Israel.
The researchers also assessed the loss of vaccine-induced protection over time based on published estimates of waning vaccine protection against infection. For the current study, the authors assumed that the likelihood of a vaccinated individual developing severe COVID-19 after being infected did not change over time. This indicated that the reduction in vaccine-induced protection against severe COVID-19 outcomes was dependent on waning vaccine protection against infection.
During the booster campaign in Israel, the general population was prioritized for vaccine administration, rather than individuals aged 60 years and above and other high-risk cohorts. The effect of boosting the low-risk populations was estimated by considering counter-factual scenarios in which the booster vaccination target groups were modified.
Results
According to the calibrated model, the absence of booster vaccines would have led to a substantial increase in COVID-19 cases, with almost 38,800 cases and approximately 810 new severe COVID-19 cases reported daily. Among these, at least 64 infections would occur in double-vaccinated individuals. These numbers were affirmed to be beyond the medical care threshold available in Israel and could have severely compromised public health.
An assessment of the situation in July indicated a critical need to apply non-pharmaceutical interventions to prevent dire COVID-19 outcomes. Furthermore, intensive research suggested that waning vaccine efficiency in Israel was the primary cause of the resurgence in the number of COVID-19 cases in the country.
Quantitative assessment of the impact of the booster vaccine administered in the Israeli vaccinated population, especially those who received the vaccine in the early stages of the pandemic, showed significant benefits of the booster in reducing both the number of infections and related hospitalizations.
The team found that delaying or advancing the distribution of vaccines by two weeks led to a significant difference in disease outcomes after booster vaccination. Furthermore, postponing the booster vaccine administration by two weeks resulted in a significantly greater disease emergence.
In individuals aged 60 years and above, the highest number of severe COVID-19 cases and related mortality were similar to those observed post booster vaccination. Comparatively, when booster vaccination was advanced by two weeks, the resurgence was curbed in the initial stage itself. This led to a further reduction of 53% in the number of confirmed infections, 51% in severe cases, and 50% in related deaths.
Among the cases that were reduced as a result of the booster vaccine, approximately 54% were decreased due to direct vaccine protection, while the remainder was a result of indirect vaccine protection. Overall, booster vaccination was found to have a quantifiable impact on the reduction of transmission and infection susceptibility.
Conclusion
Taken together, the current study findings confirm the importance of booster vaccination in reducing the resurgence of COVID-19 cases from the waning efficacy of primary vaccination. Furthermore, the model utilized in this study demonstrated that rapid implementation of a booster campaign and targeting the high-risk sub-population is essential to reducing the COVID-19 burden.
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