On Jun. 14, 2021, Kaiser Permanente Washington Health Research Institute (KPWHRI) announced that was recruiting volunteers in the Seattle area for a national clinical trial funded by the National Institutes of Health (NIH) exploring the possible benefits of pairing doses from different COVID-19 vaccines.

In the new study, KPWHRI and 8 other research centers in the Infectious Diseases Clinical Research Consortium assessed the use of different boosters that may or may not match the type of vaccine that participants received earlier. The researchers aim to determine the safety and effects of mix-and-match boosters on immunity to SARS-CoV-2, the coronavirus that causes COVID-19.

This clinical trial is currently slated to enroll approximately 400 healthy individuals ages 18 and older in the United States and will comprise 2 cohorts:

• One includes adults age 18 and older who have not received any COVID-19 vaccine. That group will first receive 2 doses of the Moderna-mRNA-1273 vaccine, which has received FDA Emergency Use Authorization, and then about 3 months later, will receive a booster of a different COVID-19 vaccine. As the trial launched, researchers aimed to find 250 participants for this cohort.
   
• The other group includes adults age 18 and older who have been fully vaccinated within the past 5 months with a COVID-19 vaccine that has received FDA Emergency Use Authorization (2 doses of Pfizer or Moderna vaccine or 1 dose of Janssen/Johnson& Johnson). These participants will receive a booster dose of the Moderna-mRNA-1273 vaccine. Researchers currently plan to recruit 150 participants for this cohort.

To gauge the potential efficacy, researchers will test how the different matches of vaccine and booster affect the levels of antibodies that help to produce an immune response to the coronavirus. The study will also track adverse events to assess the safety of the different pairings.

The need for boosters depends, in part, on whether the immune protection afforded by COVID-19 vaccines fades over time. Boosters may also be useful if new variants of the coronavirus arise that current vaccine regimens are less effective against.