US guidelines for using mRNA vaccines against COVID-19

Simon Collins, HIV i-Base

On 30 December 2020, the US guidelines on vaccines against COVID-19 were updated.

As with other guidelines on COVID-19, they are likely to be updated frequently.

Main summary

  • The current guidelines only cover the two mRNA vaccines approved in the US (Pfizer and Moderna).
  • Both vaccines require two doses – 21 and 28 days apart for the Pfizer and Moderna vaccines, respectively.
  • Caution is given it the second dose is given within a shorter window.
  • Neither vaccines has a maximum time within which the second dose should be given.
  • Although there is no preference between these two vaccines, both doses should be with the same vaccine. There is no data with mixed dosing.
  • Any other vaccines should be ideally separated by a two-week window,
  • Further boosting doses are not recommended until further data become available.
  • Vaccines can be used by people with previous COVID-19.
  • To include patient counselling on efficacy and safety.

Deferring vaccination

  • People who received monoclonal antibodies against COVID-19 or convalescent plasma are recommended to wait 90 days before using a vaccine.
  • People with current symptoms or a recent confirmed exposure should wait until quarantine restrictions are ended before having a vaccine.


The only people who are not recommended to use these vaccines

  • Severe allergy after previous mRNA COVID 19 vaccine or any of its components (listed in an appendix).
  • Any previous allergic reaction to polyethylene glycol  or polysorbate.
  • A history of severe allergy reactions to other vaccines, medicines and foods is not a contraindication to COVID-19 vaccines.
  • No underlying health conditions are a contraindication against the COVID-19 vaccines.


Several appendices are included on triage for vaccinations, ingredients in each vaccine and characterising allergic reactions.


US CDC. Interim clinical considerations for use of mRNA COVID-19 vaccines currently authorized in the United States. (30 December 2020).

This report was first posted on 5 January 2021.

Links to other websites are current at date of posting but not maintained.