evidence: Both of these vaccines require two doses. It’s after receiving your second dose that your immunity to the virus fully kicks in. You may be wondering how long after the second dose you have full immunity. [...] Pfizer-BioNTechThe Pfizer-BioNTech clinical trial evaluated vaccine effectiveness 1 week after participants had gotten their second dose. Researchers found that the vaccine was 95 percent effective at preventing COVID-19 at this point. [...] All COVID-19 vaccines have only been around for a very short amount of time. Because of this, it’s not known exactly how long immunity lasts after being vaccinated. This is true for both one-dose and two-dose vaccines.