This question has arisen more frequently since the introduction of the RSV preventive antibody, nirsevimab (Beyfortus, Sanofi), which has an injection volume of 1 mL for infants younger than 8 months who weigh 5 kg or more at the time of immunization. High risk children entering their second RSV season require a Beyfortus dose volume of 2 mL. Beyfortus is often administered at a routine visit when other infant immunizations are due.
There is no specific guidance to not exceed 1 mL in one muscle. In fact, there is no clear standard of practice and reference texts vary in guidance. Facilities or health systems may have medication policies/procedures that outline guidance for their staff. Professional judgement is needed when administering intramuscular medications or immunizations to people, including children, because muscle size varies from person to person.
CDC experts suggest a range of volume, depending upon the muscle injected. For the deltoid, the typical volume injected is 0.5 mL (maximum: 2 mL). For the vastus lateralis (the thigh): the typical volume that may be injected is 1–4 mL (maximum: 5 mL). Infants and toddlers fall at the lower end of these ranges, whereas adolescents and adults generally fall on the higher end of the range.
If more than 1 mL of volume needs to be injected into the thigh, that can be done while staying well within the acceptable range. Use of combination vaccines, when indicated and available, can decrease injection volume.
