Missourians who received the Pfizer vaccine can receive a booster shot at least six months after their initial series based on CDC guidance:

-people 65 years and older and residents in long-term care settings should receive a booster;
-people aged 50–64 years with underlying medical conditions should receive a booster;
-people aged 18–49 years with underlying medical conditions may receive a booster; and
-people aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting (e.g. frontline medical workers, teachers, and first responders) may receive a booster.

The list of medical conditions categorized as high-risk by the CDC is available here CDC COVID BOOSTER. Missourians with an underlying medical condition are encouraged to speak with their healthcare provider about whether a booster shot is right for them.