evidence: The Pfizer and Moderna vaccines are a type known as an mRNA vaccine. (Read more about COVID-19 vaccine types.) For people ages 12 and older who are unable to get an updated mRNA vaccine, or choose not to, another type of vaccine, made by the biotech company Novavax, is available. The Novavax product is a protein subunit vaccine. Two doses are recommended three weeks apart if you haven’t been vaccinated for COVID-19 before. [...] The Pfizer and Moderna vaccines are a type called a messenger RNA (mRNA) vaccine. Novavax’s is a protein-based (or protein-subunit) vaccine. All these vaccines teach the body how to fight the virus that causes COVID-19 without you actually having to get the illness. None of the vaccines causes the illness — there is no live virus in any of the vaccines. [...] Your health care team can guide you on whether you have a weakened immune system and should receive additional COVID-19 vaccinations. (The CDC has specific guidance, listed by age group, for vaccination in people with compromised immune systems.) Also, continue other COVID-19 precautions according to your health care team’s advice, including masking, distancing and frequent handwashing, and be sure people close to you are vaccinated whenever possible.