This chart shows primary vaccination progress in the people space and measures the share of the total population for each income group that is fully vaccinated as per the protocol. Note that this shows primary vaccination progress and does not include boosters.
The jagged pattern particularly for upper-middle-income countries (UMICs) reflects the fact that we show the data as made available, i.e. we do not interpolate or extrapolate observations that are missing for certain countries. The main reason for the jagged pattern of UMICs is the fact that China did not regularly disclose how doses administered resulted in full vaccination progress.
For more details on the intricacies of measuring global vaccination progress, check out this post. Other details are found below in the background section.