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Britain to Try Mix-and-Match COVID-19 Vaccinations
In the United States, the CDC has said that COVID-19 vaccines 'are not interchangeable'
MONDAY, Jan. 4, 2021 (HealthDay News) -- If a second dose of the first COVID-19 vaccine is not available or the maker is not known, then another vaccine may be used, new British guidelines say, The New York Times reported Sunday.
The new guidance contradicts those in the United States, where the U.S. Centers for Disease Control and Prevention has said that COVID-19 vaccines "are not interchangeable" and that "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."
Some experts say the British policy is gambling. "There are no data on this idea whatsoever," John Moore, Ph.D., from Weill Cornell Medical College in New York City, told The Times. Britain officials "seem to have abandoned science completely now and are just trying to guess their way out of a mess," he said.
Britain has green-lighted vaccines from Pfizer and AstraZeneca. According to the new guideline, "every effort should be made" to use the same vaccine for the second dose. But if "the same vaccine is not available, or if the first product received is unknown, it is reasonable to offer one dose of the locally available product" for the second shot.
"This option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again," the guidelines say. Because both vaccines attack the virus in the same way, "it is likely the second dose will help to boost the response to the first dose."
But there is no proof the vaccines are interchangeable.
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Primary Care
Mixing mRNA Vaccines
In primary care medical practice, we are accustomed to the occasional mixing of vaccines from different manufacturers to complete a series. This can occur when a new patient arrives for whom complete immunization records are incomplete, or during vaccine shortages. The short list of vaccines where available data support mixing include:
Fewer data are available for vaccines containing acellular pertussis. Accordingly, the same brand of DTaP vaccine should be used for all doses of the series. See “Timing and spacing of immunobiologics”1 for a complete discussion of this. In contrast, the two vaccines products for meningococcal B—owing to completely different antigens—should never be mixed.2
What then do we make of the guidance coming from the United Kingdom for COVID-19 vaccines that suggests: “If a second dose of the vaccine a patient originally received isn’t available, or if the manufacturer of the first shot isn’t known, another vaccine may be substituted”?3
The mRNA vaccines from Pfizer/BioNTech and Moderna represent a relatively new technology. They induce the production of the SARS-CoV-2 spike protein by the recipient’s cells, against which an immune response is mounted. Because of subtle differences in the mRNA strands and the carrier lipoproteins, and because of our extremely short experience with these vaccines, virtually nothing is known about the effects of following one vaccine with the other. In the midst of a national (and international) pandemic vaccine campaign, however, errors are bound to be made.
Accordingly, the CDC has issued this guidance4 for clinicians and vaccinators (I have added the italics for emphasis).
Interchangeability With Other COVID-19 Vaccine Products
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. However, if two doses of different mRNA COVID-19 vaccine products are inadvertently administered, no additional doses of either product are recommended at this time. Recommendations may be updated as further information becomes available or other vaccine types (eg, viral vector, protein subunit vaccines) are authorized.
The bottom line for practices, clinicians, and vaccinators is to ensure that the same vaccine is used for both doses. State immunization registries can help. I just checked my own record in the Wisconsin Immunization Registry, confirming that I received dose 1 of the Pfizer COVID-19 vaccine on 12/31/2020. In addition, use of the CDC’s V-Safe app (https://www.cdc.gov/coronavirus/2019-ncov/vaccines/safety/vsafe.html) can serve to remind your patients on timing of second dose and type of vaccine received, as well as serving as a tool to report any adverse effects of vaccination.
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