Atlanta, GA—While the CDC continues to emphasize that COVID-19 vaccines are not interchangeable, and the safety and efficacy of a mixed series has not been evaluated. However, there might be a circumstance, when someone who had a reaction to the first dose of an mRNA vaccine and could not complete the series, in which a person might be eligible to receive the Janssen vaccine at a later date.

In slides for a call with clinicians, the CDC describes a scenario where the “COVID-19 vaccine was received but patient unable to compete series with same or different mRNA vaccine.” In that case, it explains, a “single dose of Janssen (Johnson & Johnson) COVID-19 vaccine may be administered at minimum interval of 28 days from mRNA dose.”

In that situation, the patient would be considered “to have received valid, single-dose Janssen vaccination, not mixed vaccination series (mRNA/viral vector),” according to the presentation. The CDC speakers said more detailed guidance will be forthcoming as overall clinical considerations are updated to include the Janssen vaccine, which is of the viral-vector type. The other two COVID-19 vaccines that have received emergency use authorization were of the mRNA type.

“We are recommending if someone has completed a series [with an mRNA vaccine] ... they are considered vaccinated, they do not need any additional protection,” said Sarah Mbaeyi, MD, MPH, of the CDC’s National Center for Immunization and Respiratory Diseases. “We are not recommending people substitute in [Janssen if there’s a temporary unavailability of Pfizer or Moderna].”

The CDC presentation points out, however, that people with a contraindication to mRNA COVID-19 vaccines also have a precaution to Janssen COVID-19 vaccine. “In these patients, vaccination should be undertaken in an appropriate setting under the supervision of a healthcare provider experienced in the management of severe allergic reactions,” it advises, adding that referral to an allergist-immunologist should be considered.

In the call, public-health officials describe how the vaccine is authorized for adults aged 18 years and older and is an IM injection (0.5 ml) with no diluent required. The single-dose series requires less challenging storage than some other vaccines, with shipment and storage of up to 3 months at refrigerator temperatures and long-store at standard freezer temperatures of -20 degrees centigrade.

The presenters advise that the COVID-19 vaccine should be administered alone with minimum interval of 14 days before or after administration of other vaccines, although a shorter interval may be used in situations where the benefits of vaccination are deemed to outweigh the potential unknown risks—such as tetanus toxoid vaccine for wound management—or to avoid barriers or delays to vaccination.

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