Changing Vaccine Manufacturers Between Doses

April 2, 2021

The UK has established a vaccine protocol allowing patients to receive their first and second vaccine doses from different manufacturers. This is permissible if a second dose of the vaccine is unavailable or the manufacturer of the first dose is unknown. Currently, the only vaccines authorized for emergency use in the UK are by Pfizer, Moderna, and AstraZeneca.

The government protocol adds that “this option is preferred if the individual is likely to be at immediate high risk or is considered unlikely to attend again” (1). It is not required that patients receive a second dose if it means using a vaccine from a different manufacturer than the first dose. 

It is important to note that the Pfizer and Moderna vaccines use lipid nanoparticles (non-water-soluble liquids) to deliver the mRNA, whereas AstraZeneca uses an adenovirus to deliver a coronavirus spike protein. The double-stranded DNA is a “cousin” of mRNA, and the vehicles for delivery are unique. Trials are currently underway studying the safety and efficacy of mixing vaccines from different manufacturers. 

The CDC has made it clear that patients in the US should receive doses from the same vaccine manufacturer. The only time vaccines should be mixed is after receiving an mRNA vaccine and using a single-dose of Johnson & Johnson’s (J&J) vaccine as the second dose. The protocol for changing vaccine manufacturers between doses has not been tested and should be limited to “exceptional situations;” for example, where the patient experienced an adverse reaction after receiving the first mRNA vaccine (2). The J&J vaccine may be administered 28+ days after the first mRNA COVID-19 vaccine. Patients are encouraged to view the CDC’s list of Contraindications and Precautions beforehand if they’ve experienced an adverse reaction to the mRNA COVID-19 vaccine and are hoping to get the J&J vaccine. To learn more about getting vaccinated when you have an autoimmune disease and why contraindications can occur, check out our article. 

Because the vaccines deliver genetic material through different methods, use different fillers, and are designed to induce an immune response over a two-step process using the same delivery method, it is not yet possible to say whether interchanging vaccines will offer the same rate of efficacy or safety demonstrated in clinical trials.





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