Can you mix and match booster shots?

Approximately 20 months into a global pandemic, the United States continues to struggle with controlling the spread of the virus, COVID-19. Vaccinations to combat COVID-19 were researched and tested, leading to the first batches of the vaccines being shipped to the United States and administered to individuals in December 2020. Today, in the latter half of 2021, the U.S. is looking at providing individuals with booster vaccinations. President Biden’s administration has suggested that every American should be provided a booster dose of the vaccine, Pfizer or Moderna, as soon as September 20, 2021. However, since becoming aware of this recommendation, Americans are beginning to question the safety of mixing and matching vaccines. 

The FDA has stated that a third dose of the recommended booster vaccines, Pfizer and Moderna, will allow increased protection against COVID-19, especially for vulnerable populations. Albert Shaw, MD, Ph.D., a Yale Medicine infectious disease specialist detailed, when discussing booster vaccines, “The concept is to prolong protective immunity, particularly if there is evidence that protection is waning after a period of time.” While Americans are waiting for September 17, to hear the FDA’s decision on booster shots for the general population, clinical trials have been conducted to understand the impact of mixing COVID-19 vaccines. Multiple trials, including the Com-Cov trial, have occurred in the United Kingdom, Spain, and Germany, to evaluate combining two-dose vaccines. The vaccines being tested and mixed include AstraZeneca, Novavac, Pfizer, and Moderna. Early data collected has suggested that one AstraZeneca shot and one Pfizer shot is an effective and safe method for combatting COVID-19. However, researchers noted that when combining the vaccines, there was a higher likelihood that an individual may experience temporary side effects. Lawrence Young, a virologist at the University of Warwick, has stated that this can be due to a stronger immune response that mixing vaccines can produce. The National Institutes of Health (NIH) also began a vaccine trial in June 2021. Experts have stated that the goal of the NIH trial is to determine the advantages and disadvantages of mixing different vaccines as a booster shot. 

Globally, multiple countries have already begun to mix and match vaccines out of necessity, due to the concerns of rare blood clots with the AstraZeneca vaccine. Canada, Germany, France, Spain, and South Korea have all recommended that those who received one dose of an AstraZeneca vaccine should have a second dose of the Moderna or Pfizer vaccine, rather than an additional AstraZeneca shot. The director of the World Health Organization (WHO), Dr. Kate O’Brien, stated that “based on the basic principles of how vaccines work, we do think that the mix-and-match regimens are going to work.” This educated estimation is becoming increasingly accurate, as mixing and matching vaccine research trials have shown positive results. Additionally, the UK Deputy Chief Medical Officer, Professor Jonathan Van-Tam has detailed that mixing vaccine doses can assist in improving flexibility of booster programs, and supporting countries that are experiencing supply issues. Immunologically and historically, it makes sense to provide an additional dose of vaccine with a different platform, as seen with HIV trials and studies.  Given the early results of the research trials, COVID-19 vaccine recipients can feel more comfortable mixing and matching vaccines. However, further research must be completed to verify the efficacy and safety of mixing and matching specific COVID-19 vaccines. 


AM LLC is currently working nationwide with multiple states and public health agencies on testing, contact tracing, and vaccination programs. Counties, states, or K-12 partners that are interested in partnering with AM for COVID-19 mitigation support should contact Dr. Christopher K Orlea at

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