Just Googled how long does vaccine last --this would suggest you need to booster after 24 weeks to be protected and protect others.
To keep your vaccine credentials current for travel, you’ll want to schedule a booster shot as soon as you’re eligible. That’s the easiest way to keep your vaccination status up-to-date. After completing the booster shot, travelers should update their vaccine passport or paper CDC card with their booster shot date and vaccine lot number.
COVID-19 vaccines, like others, lose effectiveness after a certain time but still protect against severe symptoms, according to several studies. The U.S. Centers for Disease Control and Prevention reported that the Pfizer and Moderna vaccines were a whopping 84% effective at 13 to 24 weeks, or roughly three to 5.5 months. (The Johnson and Johnson vaccine was not included in the study.)
Keeping your vaccination status current is not the only consideration for travelers. There is usually a waiting period after a final dose for a person to be considered fully vaccinated, and travelers may also want to consider potential side effects. No one wants to get a booster shot, hop on a plane and feel under the weather for the first few days of vacation.