Are the mRNA vaccines interchangeable (i.e., can the doses come from different brands)?
According to the CDC, either of the currently authorized mRNA COVID-19 vaccines can be used when indicated; ACIP does not state a product preference. However, these mRNA COVID-19 vaccines are not interchangeable with each other or with other COVID-19 vaccine products. The safety and efficacy of a mixed-product series have not been evaluated. Both doses of the series should be completed with the same product. Every effort should be made to determine which vaccine product was received as the first dose, in order to ensure completion of the vaccine series with the same product.
In exceptional situations in which the mRNA vaccine product given for the first dose cannot be determined or is no longer available, any available mRNA COVID-19 vaccine may be administered at a minimum interval of 28 days between doses to complete the mRNA COVID-19 vaccination series. In situations where the same mRNA vaccine product is temporarily unavailable, it is preferable to delay the second dose (up to 6 weeks) to receive the same product than to receive a mixed series using a different product. If two doses of different mRNA COVID-19 vaccine products are administered in these situations (or inadvertently), no additional doses of either product are recommended at this time. Such persons are considered fully vaccinated against COVID-19 ≥2 weeks after receipt of the second dose of an mRNA vaccine.
In limited, exceptional situations where a patient received the first dose of an mRNA Covid-19 vaccine but is unable to complete the series with either the same or different mRNA Covid-19 vaccine (e.g., due to contraindication), a single dose of Johnson & Johnson Covid-19 vaccine may be considered at a minimum interval of 28 days from the mRNA Covid-19 vaccine dose. Patients who receive Johnson an& Johnson vaccine after a dose of an mRNA vaccine should be considered to have received a valid, single-dose Johnson & Johnson vaccination—not a mixed vaccination series—and are considered fully vaccinated against COVID-19 ≥2 weeks after receipt of the single dose of the Janssen vaccine.