Shingrix, the recommended vaccine for shingles prevention, is indicated to be given by IM (intramuscular) injection in the deltoid.
However, if there is an administration error, and it is accidentally given SQ (subcutaneously), the CDC (Centers for Disease Control) states that it should be counted as a valid dose. It does not need to be re-administered in the muscle.
Per the CDC:
Shingrix should be injected intramuscularly in the deltoid region of the upper arm. Subcutaneous injection is a vaccine administration error and should be avoided. However, if you inadvertently administer Shingrix subcutaneously, that dose is considered valid and does not need to be repeated. If a subcutaneous vaccine administration error occurs on the first dose of Shingrix, a second dose is still required after 2 – 6 months.
For reference, here is an image provided by the CDC showing the appropriate administration site:
IM Vs. SQ
There are many reasons why some vaccines are recommended to be given IM while others are recommended to be given SQ.
The 'Ask The Experts' section on the Immunization Action Coalition website provides a good summary:
In general, vaccines containing adjuvants (a component that enhances the antigenic response) are administered IM to avoid irritation, induration, skin discoloration, inflammation, and granuloma formation if injected into subcutaneous tissue. This includes most of the inactivated vaccines, with a few exceptions (such as IPV and pneumococcal polysaccharide vaccines, which may be given either SC or IM). Vaccine efficacy may also be reduced if not given by the recommended route.
Although a dose of Shingrix isn't recommended to be repeated if it is accidentally given subcutaneously, there, unfortunately, is no data regarding whether or not there will be an increase in the incidence of side effects.
Since Shingrix contains an adjuvant (AS01B), it stands to reason that an SQ injection will likely cause more pain and inflammation than if it were given IM.
In regard to SQ administration decreasing the overall effectiveness of the vaccine, this isn't entirely known as well. Studies show that there is a definite immune response, however. Per the Immunization Action Coalition 'Ask The Experts":
Q: A patient was inadvertently given RZV [Shingrix] by the subcutaneous rather than the intramuscular route. Does the dose need to be repeated?
A: RZV has been shown to be immunogenic when given by the subcutaneous route. A dose erroneously given by this route does not need to be repeated.
If you accidentally administered Shingrix subcutaneously, it is recommended to report the error to the Institute for Safe Medication Practices (ISMP), specifically to their Vaccine Error Reporting Program (VERP). This program allows you to report any vaccine error confidentially, and the information collected is used to provide education for future error prevention.
SummaryShingrix should be given intramuscularly (IM). However, if it is accidentally administered SQ (subcutaneously), the dose does not need to be repeated according to the Immunization Action Coalition.