Here's How to Avoid a COVID
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Here's How to Avoid a COVID

Aug 12, 2023

by Shannon Firth, Washington Correspondent, MedPage Today September 16, 2022

Recognizing the potential for vaccine administration errors with look-alike vials, CDC staff shared best practices for giving the right vaccine to the right person at the right dose, during a Clinician Outreach and Communication Activity (COCA) webinar earlier this week.

The most concerning possible vaccination error would be that a child might receive a higher dose of vaccine than indicated for his or her age, because of the potential for increased reactogenicity -- for example an arm that is more sore than normal or a fever -- Elisha Hall, PhD, Clinical Guidelines Lead and a Health Education Specialist for the CDC, told MedPage Today in a follow-up phone call.

In the case of an adult who has inadvertently been given a child's dose, "the concern is less about safety and more immunologic," she said.

One strategy for preventing vaccine mix-ups is to be aware of the similarities between vials for different age groups and purposes.


Both Pfizer's monovalent primary series vial and its bivalent booster vial for individuals 12 years and older have border labels and caps that are an identical gray color. The total dose amounts are the same for both, but the monovalent vaccine only targets the ancestral strain of the virus, while the bivalent vaccine has components targeting both the ancestral and Omicron BA.4/BA.5 strains.

Differentiating vials by cap color is not very effective, because once a multi-dose vial is ready to be punctured "that cap is gone, and the color-identifier is gone."

So, it's more important to look at the label and title, Hall said.

Unfortunately, in Pfizer's case the borders again are the same color for both the bivalent and monovalent vaccine vials. The only clear difference is the wording:

Fortunately, the 5-11 year old primary vaccine border label is different, Hall noted.


For the Moderna vaccine, some obvious differences in appearance exist between the monovalent vaccine (primary series dose for individuals 12 and over) and bivalent booster vaccine (for adults 18 and over) vials. The monovalent vial cap is red while the bivalent vaccine vial is dark blue, which is only useful for vials that haven't already been uncapped and used.

In addition, the label border color for the monovalent vaccine is light blue, while the label border color for the bivalent vaccine is gray.

The caps of the monovalent children's dose (primary series for individuals 6-11) and bivalent vaccine booster doses (for adults 18 and older) are both dark blue. However, the label border color for the monovalent vaccine for children 6-11 is purple and the label border color for the bivalent booster vaccine for those 18 and older is gray.

To add to the confusion, the primary series vaccine label for the 6-11 group says "booster doses only," because when the vaccines for young children were first authorized the appropriate vials weren't available, but the dose for this age group is the same as the dose of Moderna's original monovalent booster dose for adults.

The most expected error "would probably be mixing up the 6-11 monovalent product with the 18 year and older bivalent product," Hall noted.

As for best practices for avoiding mixing up vaccine vials, Hall, in her COCA presentation listed the following tips:

CDC also offered several recommendations for safe preparation and administration:

Many pharmacies and practices use only one vaccine product, either Moderna or Pfizer, Hall noted. And those that carry both may designate days for each -- for example, Moderna on Mondays. Providers may also choose to designate one day for children's vaccines and another for adults.

If a vaccine administration error does occur, the next action depends on the type of error that occurred.

Bivalent Booster Dose

If a bivalent Pfizer vaccine is given in place of a Pfizer primary series monovalent vaccine, the CDC recommends not repeating the dose and instead counting it.

If a bivalent Moderna vaccine is given in place of a Moderna primary series vaccine dose, Hall advised administering one monovalent dose immediately afterwards, without a minimum interval as the repeat dose, "because administration of the booster dose results in a lower than authorized dose for the primary series."

That interval can be extended for individuals at high-risk of a reaction, for example myocarditis or pericarditis.

Monovalent Vaccine Dose

If a monovalent vaccine dose is accidentally given in place of a bivalent booster dose, and a bivalent is indicated, for those 12 and older, the CDC recommends not repeating the dose, but a provider may give a bivalent booster dose as a repeat dose "based on clinical judgment and patient preference," Hall noted during the webinar. Any repeat dose should be administered at least 2 months after the dose given by mistake.

Next Steps

For any vaccine administration errors, clinicians should inform the patient, consult with the state program, and report the error to the Vaccine Adverse Events Reporting System (VAERS). Hall also stressed the need to investigate how the error occurred in order to develop strategies to ensure it won't be repeated.

Broadly speaking, the CDC has not seen additional adverse events associated with reports of vaccination errors, Hall said in a follow-up email.

As of August 21, the only serious adverse event report associated with a vaccination error related to a "syringe malfunction," she noted. Vaccine leaked or squirted onto a child with a history of eczema, resulting in a partial dose, she noted.

The child subsequently received a full dose during the same visit. She developed a "generalized rash" and "lip swelling" later the same day, and based on that description, "met the case definition for anaphylaxis."

Some adverse events may be "coincidental events" and others are true adverse reactions, she noted.

As to whether there has been a spike in vaccine errors since the bivalent booster doses were authorized, Hall said it's "too early" to tell and "data are too sparse."

Hall recommended, for any other concerns, consulting the detailed table in the appendix of the CDC's interim recommendations that focuses on COVID-19 administration errors and deviations.

Shannon Firth has been reporting on health policy as MedPage Today's Washington correspondent since 2014. She is also a member of the site's Enterprise & Investigative Reporting team. Follow

Pfizer/BioNTechModernaBivalent Booster DoseMonovalent Vaccine DoseNext Steps