From the Guidelines
If a patient accidentally receives a double dose of varicella vaccine, no specific treatment is needed and no adverse consequences are expected. The patient should be monitored for typical vaccine side effects such as soreness at the injection site, mild fever, or rash, which may be slightly more pronounced but remain self-limiting. The double dose does not require restarting the vaccination schedule, and future doses (if any are needed) should be administered according to the regular schedule. This recommendation is based on the safety profile of varicella vaccine, which has a wide margin of safety, as reported in a study published in 2011 1. The vaccine contains attenuated (weakened) virus that stimulates immunity without causing disease, and while a double dose provides more antigen than intended, the immune system processes it without significant additional risk. Parents or patients should be reassured that such dosing errors, while not ideal, are unlikely to cause harm beyond potentially increased mild side effects. Key points to consider include:
- The varicella vaccine has an excellent safety profile, with the most common adverse events being injection-site complaints and varicella-like rash at the injection site 1.
- The risk of transmission of vaccine virus from immunocompetent vaccine recipients is extremely low, and no cases of transmission have occurred after immunization of health care professionals 1.
- The benefits of vaccinating susceptible individuals outweigh the negligible potential risk of transmission 1. It is essential to prioritize the patient's safety and well-being, and in this case, the risk of adverse consequences from a double dose of varicella vaccine is extremely low, as supported by the evidence from the study published in 2011 1.
From the Research
Accidental Double Dose of Varicella Vaccine
- The administration of an extra dose of a vaccine, including varicella, may occur due to programmatic errors or uncertain vaccination histories 2.
- Studies have shown that the most common adverse events (AEs) reported after an excess dose of vaccine, including varicella, were pyrexia, injection site erythema, injection site pain, and headache 2.
- A study on the safety of a second dose of varicella vaccine administered at 4 to 6 years of age in healthy children in Argentina found that the vaccine was well tolerated and showed no significant safety issues 3.
- Another study on the safety of second-dose single-antigen varicella vaccine found that the most common AEs were injection site reactions, and no new or unexpected safety concerns were identified 4.
Safety of Varicella Vaccines
- The Vaccine Adverse Event Reporting System (VAERS) has been used to monitor the safety of varicella vaccines, including single-antigen varicella vaccine (VAR) and combination measles, mumps, rubella, and varicella vaccine (MMRV) 5.
- A study on the safety surveillance of varicella vaccines in the VAERS found that the most common adverse health events after both VAR and MMRV were injection site reactions, rash, and fever 5.
- Large injection site reactions after a second dose of varicella vaccine have been reported, but these reactions resolved with symptomatic therapy 6.
Adverse Events
- The most common AEs reported after an excess dose of varicella vaccine were comparable to those reported for all vaccines during the same period 2.
- Serious reports of selected AEs, including anaphylaxis, meningitis, encephalitis, and cellulitis, have been identified, but these were not unexpected or new safety concerns 4, 5.
- Vaccination errors accounted for a significant proportion of reports after varicella vaccine administration, but most of these did not describe an adverse health event 5.