The CDC preferentially recommends individuals receive mRNA vaccines - Moderna or Pfizer - for the prevention of COVID-19 over the Johnson & Johnson vaccine. This recommendation follows similar recommendations from other countries such as Canada and the United Kingdom. The decision to preferentially recommend mRNA vaccines was based on evolving evidence on vaccine safety, effectiveness, and adverse events.
The Baltimore City Health Department recommends that all eligible residents receive the mRNA vaccine - Moderna or Pfizer - for their primary series (first two doses) and their booster. If an individual 18 years and older is unable to receive a mRNA vaccine due to a history of allergic reactions, anaphylaxis, or other contraindication a Johnson & Johnson booster may be given.
The CDC Endorses ACIP’s Updated COVID-19 Vaccine Recommendations.