In a recent study Science Translational Medicine Researchers are evaluating the impact of the 2019 coronavirus (COVID-19) booster vaccine on the Israeli population.
In June 2021, the Israeli population witnessed a notable surge in COVID-19 breakthrough cases. During this period, nearly 80% of the vaccineeable population was vaccinated with two doses of BNT162b2 vaccine. It therefore seemed necessary to authorize the administration of a booster vaccine in Israel.
To learn : Impact of the Israeli recall at the population level to contain the resurgence of COVID-19. Photo credit: insta_photos / Shutterstock.com
About the study
In the present study, the researchers analyze the impact of different aspects of the population-level booster vaccination campaign on the outcome of COVID-19 disease in Israel.
The fourth wave of COVID-19 in Israel occurred between July 1, 2021 and November 25, 2021. The team developed an age-stratified transmission model of discrete-time infection that took into account the initial vaccination and booster vaccination as well as the decrease in vaccine immunity over time. The model was calibrated and validated against national data including number of infections, disease severity and reported immunizations. All data were stratified by age, immunization status, and daily resolutions.
Demographic data collected for each individual included age, location, polymerase chain reaction (PCR) test dates, first, second and third vaccination dates, COVID-19-related hospitalizations and death. The study included all severe fourth-wave PCR-positive COVID-19 cases in Israel.
Researchers also assessed the loss of vaccine-induced protection over time based on published estimates of the weakening of vaccine protection from infection. For the current study, the authors assumed that the likelihood of a vaccinated person developing severe COVID-19 disease after infection does not change over time. This indicates that the reduction in vaccine-induced protection from severe COVID-19 was dependent on the weakening of vaccine protection from infection.
During the booster campaign in Israel, priority was given to administering the vaccine to the general population, rather than those aged 60 and over and other high-risk groups. The effect of boosting low-risk populations was estimated taking into account counterfactual scenarios in which the target populations for the booster were changed.
According to the calibrated model, the lack of booster shots would have resulted in a significant increase in COVID-19 cases, with nearly 38,800 cases and about 810 new severe cases of COVID-19 reported daily. Of these, at least 64 infections are said to have occurred in double-vaccinated people. It was claimed that these numbers exceeded the threshold of medical care available in Israel and could pose a serious risk to public health.
An assessment of the situation in July showed that it is absolutely necessary to use non-pharmaceutical interventions to prevent the catastrophic consequences of COVID-19. In addition, intensive research has found that the declining effectiveness of vaccines in Israel is the main reason for the resurgence in the number of COVID-19 cases in the country.
Quantitative assessment of the effect of the booster vaccine administered to the vaccinated Israeli population, particularly those who received the vaccine at the beginning of the pandemic, showed that the booster vaccine significantly reduced the number of infections and hospital admissions.
The team found that delaying or advancing the distribution of vaccines by two weeks made a significant difference in disease progression after the booster dose. In addition, the two-week delay in booster vaccination resulted in a significantly higher incidence of disease.
In people 60 years and older, the peak number of severe COVID-19 cases and associated mortality was similar to that observed after the booster dose. On the other hand, when the booster vaccination was brought forward by two weeks, the resurgence was stopped at the early stage. This resulted in a further 53% drop in confirmed infections, 51% in severe cases and 50% in associated deaths.
Of the cases reduced with the booster vaccine, approximately 54% were reduced due to direct vaccine protection, while the remainder were the result of indirect vaccine protection. Overall, booster vaccination was found to have a quantifiable impact on reducing transmission and susceptibility to infection.
Overall, the results of the present study support the importance of booster vaccination in reducing recurrence of COVID-19 cases due to the decreasing effectiveness of primary vaccination. In addition, the model used in this study demonstrated that executing a recall quickly and targeting the high-risk subpopulation are essential to reduce the burden of COVID-19.