Heterologous vaccine schedules consist of the use of different vaccines (different brand or platform vaccine) as part of the same schedule. Vaccination with heterologous vaccines is a relatively common practice in vaccinology.
While there are currently no data for heterologous priming with other vaccine products, a large number of clinical studies of various vaccine combinations and schedules are currently ongoing.
There are currently limited data on the immunogenicity or efficacy of a ‘mix and match’ regimen. The COVID-19 vaccines with WHO Emergency Use Listing (EUL) have only been assessed as single product regimens. However, based on emerging evidence from conducted studies, the AstraZeneca recommendations have been modified to indicate that either of the mRNA vaccines (Pfizer-BioNTech or Moderna) can be used as a second dose following a first dose with the AstraZeneca vaccine, if a second dose of AstraZeneca vaccine is not available. Based on the basic principles of how vaccines work, WHO is of the view that the mix and match regimens are likely to work. However, we really need to carefully analyze the evidence in each of these vaccine combinations before any other recommendations can be made. WHO will review through its Strategic Advisory Group of Experts on Immunization (SAGE) these data as they become available, and update the recommendations accordingly.
- There is currently limited data on the immunogenicity or efficacy of a ‘mix and match’ regimen.