Despite decreases of invalid vaccine doses, series completion still lacks | Image Credit: © Lumeez23/peopleimages.com - © Lumeez23/peopleimages.com - stock.adobe.com.

Vaccine doses provided to children outside of the CDC's Advisory Committee on Immunization Practices' (ACIP) recommendations for minimum and maximum ages of vaccination and minimum intervals are considered invalid. According to new research published in Pediatrics, invalid vaccine doses have decreased over time, however many children with an invalid dose lack full vaccination series completion.^1,2

Study details

With the objective to quantify the prevalence of and factors associated with invalid doses among children aged 0 to 35 months in the United States, the study authors analyzed provider-verified vaccination records from the nationally representative 2011–2020 National Immunization Survey–Child.¹

"We quantified the number of children with at least 1 invalid vaccine dose overall, by survey year, and by vaccine type," stated the investigators, led by Alexandria N. Albers, MPH, MS, of the Center for Population Health Research, University of Montana and the School of Public and Community Health Sciences, Missoula, Montana.¹
"Among children who received vaccine doses before the minimum age or minimum dose interval, we quantified the prevalence of receiving extra doses such that series were completed with the recommended number of valid doses," stated Albers and authors.¹

The investigators included all 10 recommended vaccination series during the study period, which included:

• Diphtheria, tetanus, acellular pertussis
• Varicella
• Hepatitis B
• Measles, mumps, rubella
• Inactivated poliovirus vaccine
• Pneumococcal conjugate vaccine
• Haemophilus influenzae type b (Hib)
• Hepatitis A
• Rotavirus
• Influenza

RELATED: Kindergarten vaccine coverage decreased, exemptions increased in 2023-2024 school year

"ACIP guidelines allow for a 4-day grace period, which we incorporated in our analyses," said Albers in a featured video on the Pediatrics website.¹

"We reviewed current and historical ACIP schedules, and for each vaccine dose, we determined the minimum recommended age in days for vaccination and the minimum interval between doses for multi-dose series."

The investigative team used logistic regression models to identify factors associated with the receipt of an invalid vaccination.¹

Results

Of the 161,187 children in the survey, 22,209 (weighted percent for US children: 15.4%, 95% CI, 15.0%–15.8%) received an invalid vaccine dose. Of those with a minimum age or minimum interval invalid dose, 44.9% (95% CI, 43.2%–46.6%) received extra doses and completed the series.¹

The 3-dose rotavirus had the highest prevalence of invalid doses (n = 5733; 4.4%), with the first dose being administered after the maximum age (n = 3996; 3.1%), according to study results.¹

"Receiving the third dose of the 3-dose Hib series too soon was another top reason for invalid doses," said Albers in the Pediatrics video. "However, 84% of children with an invalid Hib dose also had a repeat valid vaccination to essentially correct the invalid Hib dose."¹

Results demonstrated that factors associated with at least 1 invalid vaccination dose were if the child had 3 or more vaccination providers compared to 1 provider (aOR: 1.5, 95% CI, 1.2-1.8), or if they moved across state lines compared to children who did not move (aOR: 1.5, 95% CI, 1.4-1.6).¹

Conclusion

"Although invalid vaccine doses have decreased over time, many children with invalid doses lacked the doses necessary to complete a vaccine series," concluded Albers and investigators.¹

ACIP has a detailed child and adolescent immunization schedule by age. Click here to view it.²

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ACIP recommends ≥1 updated COVID-19 vaccine booster for all children, adolescents

References:

1. Alexandria N. Albers, Sarah Y. Michels, Matthew F. Daley, Jason M. Glanz, Sophia R. Newcomer; Invalid Vaccine Doses Among Children Aged 0 to 35 Months: 2011 to 2020. Pediatrics 2025; e2024068341. 10.1542/peds.2024-068341

2. Child and adolescent immunization schedule by age. CDC. Updated November 21, 2024. Accessed January 14, 2024. https://www.cdc.gov/vaccines/hcp/imz-schedules/child-adolescent-age.html