This is a more challenging question to answer since researchers keep learning more about how long the protection from the vaccines lasts. The Moderna vaccine contains a larger dose of mRNA than the Pfizer vaccine. Nonserious side effects, such as flu-like symptoms, are apparently more common with the Moderna vaccine. Some preliminary evidence also indicates that the Moderna vaccine may trigger immunity that lasts longer than the immunity from the Pfizer vaccine. However, both of these vaccines provide great protection against getting seriously ill with COVID-19.