Impact of vaccination and undetected cases on the COVID-19 pandemic dynamics in Qatar in 2021

The third COVID-19 pandemic wave in Qatar was simulated with the use of the generalized SIR-model and the accumulated number of cases reported by Johns Hopkins University for the period: April 25 - May 8, 2021. Comparison with the SIR-curves calculated before for the second wave showed that the effect of mass vaccination is not evident during 4 months after its onset in December 2020. Additional simulations have demonstrated that many COVID-19 cases are not detected. The real accumulated number of cases can exceed the laboratory-confirmed one more than 5 times. This fact drastically increases the probability of meeting an infectious person and the epidemic duration.