According to the National Institutes of Health, although vaccines against COVID-19 have a high level of efficacy, especially for hospitalization and serious illness, some vaccines are not 100% effective.
As a result, despite being vaccinated, there is a small percentage of vaccinated people who become infected with COVID-19.
In addition to the specific characteristics of the vaccine, factors such as age, underlying disease, previous COVID-19 disease, current exposure to SARS-CoV-2, or circulation of virus strains may affect the effectiveness of the vaccine.
