There’s no reason to believe that the COVID-19 vaccine can change your period. Know that the CDC and other researchers are continuing to monitor the COVID-19 vaccines for serious side effects using well-established vaccine safety monitoring systems.
There are many reasons your period may be different. Things like stress, being sick, taking certain medicines, and hormonal changes can affect your period. If changes in your period keep happening, contact your nurse or doctor, like the ones at your local Planned Parenthood health center.