Unlike the relatively new technologies that the mRNA and viral-vector COVID-19 shots are based on, protein vaccines have been used for decades to protect people from hepatitis, shingles and other viral infections.

To elicit a protective immune response, these shots deliver proteins, along with immunity-stimulating adjuvants, directly to a person’s cells, rather than a fragment of genetic code that the cells must read to synthesize the proteins themselves.

Although protein vaccines are not yet in widespread use for COVID-19, late-stage clinical-trial data so far look promising, demonstrating strong protection with fewer side effects than other COVID-19 shots typically cause.

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