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Covid Q&A: Can I Mix Pfizer and Moderna Vaccines?

In this week's edition of the Covid Q&A, we look at whether it's OK to mix doses of different Covid-19 vaccines.

In hopes of making this very confusing time just a little less so, each week Bloomberg Prognosis is picking one question sent in by readers and putting it to an expert in the field. This week's question comes to us from Phillip, who has received his first dose of a Covid-19 vaccine from Pfizer-BioNTech. As vaccine supplies dwindle, he wonders whether it's safe to receive the Moderna vaccine instead as his second dose. He asks:

What would happen if only Moderna doses are available? Are they interchangeable? Is it safe to switch?

This is a great question, and one that many other newsletter readers raised this past week. The Moderna and Pfizer vaccines are remarkably similar. Each uses a technology called messenger RNA (mRNA) to teach cells how to make a protein that will trigger an immune response to the virus, preparing the body for a potential encounter with it in the wild.