For whatever reasons, vaccine arrived later in some countries.
For whatever other reasons, some people had chosen to ‘opt out’ in those countries where the vaccine had been plentiful.

The results have been the same.

More than half of Vietnam’s people are currently under lockdown.
New daily cases have surpassed 10,000 and deaths are being reported in hundreds. Of Vietnam’s nearly 16,000 COVID-19 fatalities, more than 99% have come in this latest wave
.”

https://www.npr.org/2021/09/16/1037768399/long-weekend-becomes-9-week-lockdown-for-ap-vietnam-reporter
https://www.inquirer.com/health/coronavirus/pennsylvania-coronavirus-breakthrough-cases-vaccinated-unvaccinated-20210914.html