While several COVID-19 vaccines appear to have high levels of efficacy, no vaccine is 100% protective. As a result, there may be a small percentage of people who do not develop protection as expected after COVID-19 vaccination.

In addition to a vaccine's specific characteristics, several factors such as a person's age, their underlying health conditions or previous exposure to COVID-19 may have an impact on a vaccine's effectiveness. We also do not yet know how long immunity from different COVID-19 vaccines will last. That is one reason why, even as COVID-19 vaccines start to be rolled out, we must continue using all public health measures that work, such as physical distancing, masks, and handwashing.