On December 23rd the Czech government has issued a new regulation on entry to the Czech Republic, which will apply from December 27th, 2021.
On the one hand, this means that people who have been vaccinated twice must show a negative PCR test. The only exceptions are people with a booster vaccination and children. In some cases, an antigen test is sufficient.
On the other hand, small border traffic will be suspended from December 30th, 2021 to January 1st, 2022. During those three days the same rules apply to short trips to the Czech Republic as to longer visits.
Cross-border commuters are not affected by these new regulations.