Impact of booster COVID-19 vaccine for Moroccan adults: A discrete age-structured model approach

Public health control strategies, such as lockdown, seem to be effective in reducing the spread of the pandemic, but are ineffective as a whole since lockdown is responsible of global economic crisis and badly lived by the majority of children and adults who have developed mental health disorders and familial problems as well. Thus, the development of a vaccine against COVID-19 is needed to control this disease. We have developed a discrete age-structured model and followed the Moroccan vaccination program to assess the impact of booster vaccination targeting Moroccan adults against COVID-19. Using the derived model, we estimated some relevant model parameters related to COVID-19 using collected cumulative mortality and reported Moroccan data. A control reproduction number Rc, which determines the necessary level of vaccine uptake that lead to COVID-19 eradication is determined. Furthermore, a herd immunity threshold above which the population can be protected from COVID-19 infection is derived. Analyzing the model, sufficient and necessary conditions for the eradication of the disease are obtained as well. Next, we perform numerical simulations to study the impact of several uptake levels of the potential vaccine on the persistence and the extinction of COVID-19 pandemic. Our results show that the COVID-19 is expected to last past 2021 in the absence of a vaccination program. Moreover, a vaccination of the adult population at rate 0.6% per day needs at least 67% of vaccine efficacy and 90% of immunogenicity rate to eradicate the disease. Using Sinopharm vaccine, the herd immunity can be achieved when about half of Moroccan adult population is immunized against the COVID-19. However, using Oxford-Astrazeneca vaccine, less than 60% of adult population must be immunized against the disease to achieve the herd immunity. Finally, if vaccine efficacy is about 80% and the immunogenicity is about 50% then vaccinating adults at rate of 0.6% per day could protect roughly 22% of children from COVID-19 infection.