Childhood Vaccination Coverage Before and During the COVID-19 Pandemic among Children Born January 2017-May 2020, National Immunization Survey-Child (NIS-Child), 2018-2021

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Background and Purpose

The Advisory Committee on Immunization Practices (ACIP) recommends routine vaccination against 14 diseases during the first 24 months of life. (1) On January 13, 2023, CDC released a report using data from the National Immunization Survey-Child (NIS-Child) presenting estimates of routine childhood vaccination coverage by age 24 months for children born in 2018 and 2019. (2) This report provides additional information on the potential effect of the COVID-19 pandemic on routine childhood vaccination coverage, comparing vaccination coverage for children who reached key milestone ages before March 2020 (pre-pandemic period) and during March 2020 or later (during-pandemic period).

Methods

NIS-Child collects data from households with children aged 19-35 months. Parents complete a telephone survey, and vaccination information is obtained by mailed survey from the children’s healthcare providers. (2) CDC analyzed data for 48,576 children from survey years 2018-2021 of the NIS-Child. Vaccination coverage was estimated by month and year of birth from January 2017 through May 2020. Kaplan-Meier estimation was used to account for censoring of vaccination status at ages over 19 months. The effect of COVID-19 on routine childhood vaccination was assessed by comparing coverage among children reaching selected milestone ages (8, 13, 16, 19, and 24 months) prior to March 2020 (pre-pandemic) with coverage among children reaching these milestone ages in March 2020 or later (during-pandemic). The start of the pre-pandemic period was set at birth month January 2017 to assure adequate sample size in each of the monthly birth cohorts. The during-pandemic period ends with birth month May 2020, as children from that birth cohort turned 19 months (the youngest children included in NIS-Child) at the end of the most recent data collection period in December of 2021. Overall national-level analysis was conducted by month and year of birth, including linear trends for pre-pandemic and during-pandemic periods. Differences in vaccination coverage (during-pandemic minus pre-pandemic estimates) were computed overall nationally, and stratified by geographic area, race/ethnicity, poverty status, health insurance status, and Metropolitan Statistical Area (MSA) status.  Analyses were conducted using SAS-Callable SUDAAN (version 11; RTI International). P-values < 0.05 were considered statistically significant. This activity was reviewed by CDC and was conducted consistent with applicable federal law and CDC policy.

Results

Vaccination Coverage by Month and Year of Birth

Tables 1 (a-e) provide national coverage estimates for selected vaccines by month and year of birth for children reaching milestone ages (8, 13, 16, 19, and 24 months) prior to the start of the COVID-19 pandemic in March 2020 and those reaching these ages during the pandemic (March 2020 or later; shaded in blue). Statistical testing using z-tests was performed comparing during-pandemic estimates by month and year of birth with aggregated pre-pandemic estimates. For the 8-month milestone age (Table 1a), during-pandemic coverage estimates were higher than pre-pandemic estimates for ≥3 doses of PCV among children born July 2019 and for ≥3 doses of PCV, the HepB birth dose, rotavirus vaccine, and ≥2 doses of poliovirus vaccine among children born March 2020. For children reaching 13 months, during-pandemic estimates were higher for some vaccines and birth cohorts and lower for others (Table 1b). For both ≥1 dose of MMR and ≥1 dose of VAR, coverage decreased among children born March-April 2019 (reaching 13 months in April-May 2020) and then rebounded to values higher than the aggregate pre-pandemic estimates the following month (birth cohort May 2019). Drops in coverage compared to pre-pandemic levels were also found for ≥4 doses of PCV (born March 2019) and ≥1 dose of HepA (born April 2019). No decreases in during-pandemic coverage were seen for ≥3 doses of DTaP, ≥3 doses of poliovirus vaccine, ≥3 doses of HepB, or ≥3 doses of PCV. For the 16-month milestone (Table 1c), only two coverage estimates were lower in the during-pandemic period: ≥4 doses of DTaP and Hib-Full Series (FS) among children born December 2018 (reaching 16 months in April of 2020). Coverage for seven monthly birth cohorts (ranging from November 2018 to May 2020) was higher in the during-pandemic period. At 19 months (Table 1d), coverage for 14 monthly birth cohort/vaccine combinations was higher in the during-pandemic period compared with the aggregate pre-pandemic period. Only three coverage estimates were lower in the during-pandemic period, including Hib-FS among children born March 2019, and the combined 7-vaccine series among children born March 2019 and February 2020. For ≥3 doses of poliovirus vaccine and ≥3 doses of HepB, the aggregate during-pandemic estimate was higher than the aggregate pre-pandemic estimate. For children reaching 24 months (Table 1e), only two during-pandemic coverage estimates were lower than the corresponding aggregate pre-pandemic estimates, and both were estimates of coverage with the combined 7-vaccine series. The during-pandemic estimate was higher for 43 birth cohort/vaccine combinations involving all assessed vaccines with the exception of ≥2 doses of HepA. The aggregate during-pandemic estimates were higher than aggregate pre-pandemic estimates for ≥3 doses of poliovirus, ≥3 doses of HepB, ≥4 doses of PCV, ≥1 dose of HepA, and ≥2 doses of influenza.

Tables 2 (a-e) describe national trends in coverage with selected vaccines by month and year of birth during the pre-pandemic and during-pandemic periods stratified by milestone ages (8, 13, 16, 19, and 24 months). Trends are based on slopes from weighted linear regression analysis of estimated vaccination coverage by month and year of birth using the inverse variances of the estimates as the weights. For children reaching 8 months prior to and during the pandemic (Table 2a), pre-pandemic coverage was trending upward for four of the six vaccines assessed (≥3 doses of DTaP, ≥3 doses of PCV, the HepB birth dose, and rotavirus). Except for the HepB birth dose, there was no longer a trend in coverage during the pandemic period. For the HepB birth dose, coverage appears to have increased even faster during the pandemic period compared with the pre-pandemic period. At 13 months (Table 2b), trends in coverage were positive prior to the pandemic for most vaccines evaluated. These trends were no longer apparent in the during-pandemic period. A similar pattern was seen for the 16-month milestone (Table 2c), with several positive slopes prior to the pandemic but no discernable trends during the pandemic. At 19 months (Table 2d), coverage with ≥4 doses of DTaP was stable prior to the pandemic but began increasing during the pandemic. The reverse was seen for ≥1 dose of MMR, ≥3 doses of HepB, and ≥1 dose of HepA, with positive slopes prior to the pandemic and no changes in coverage during the pandemic. Children reaching 24 months (Table 2e) prior to the pandemic had increasing coverage with ≥4 doses of DTaP, Hib-FS, and ≥2 doses of HepA; no trends in coverage were evident for those reaching 24 months during the pandemic.

Vaccination Coverage for Pre-Pandemic and During Pandemic Cohorts, by Geographic Area

Tables 3 (a-e) provide aggregate pre-pandemic and during-pandemic coverage estimates for milestone ages (8, 13, 16, 19, and 24 months), by jurisdiction (US national, HHS region, state (including District of Columbia), selected local area, and territory). At the 8-month milestone (Table 3a), seven coverage estimates decreased during the pandemic period, including those for: ≥3 doses of DTaP (City of New York and Puerto Rico); Hib-Primary Series (Puerto Rico); ≥3 doses of PCV (Puerto Rico); and rotavirus (Maine, New Hampshire, Puerto Rico). Coverage increased during the pandemic period for 26 other vaccine/jurisdiction combinations. For children reaching 13 months (Table 3b), 19 coverage estimates were lower during the pandemic period, including those for: ≥3 doses of DTaP (Puerto Rico); ≥3 doses of poliovirus vaccine (Puerto Rico); ≥1 dose of MMR (Arkansas, Puerto Rico); Hib-PS (West Virginia, Arizona, Puerto Rico); ≥3 doses of HepB (Arizona, Puerto Rico); ≥1 doses of VAR (City of New York, City of Chicago, Arkansas, Oregon, and Puerto Rico); ≥3 doses of PCV (Puerto Rico); ≥4 dose of PCV (Arkansas, Alaska); and ≥1 dose of HepA (Arkansas, Puerto Rico). An additional 32 vaccine/jurisdiction combinations were associated with higher coverage in the pandemic period. For children reaching 16 months (Table 3c), there was evidence of lower during-pandemic coverage for 27 vaccine/jurisdiction combinations, including: ≥4 doses of DTaP (Rhode Island, District of Columbia, Maryland); ≥3 doses of poliovirus vaccine (Puerto Rico); ≥1 dose MMR (Illinois, Illinois excluding Chicago; Arkansas, Puerto Rico); Hib-FS (HHS Region 1, New Hampshire, HHS Region 2, New York, Maryland, Philadelphia, Minnesota, Arkansas, Arizona, Alaska); ≥3 doses of HepB (Missouri, Arizona, Puerto Rico); ≥1 dose of VAR (Puerto Rico); ≥4 doses of PCV (New Hampshire, HHS Region 2, Maryland); and ≥1 dose of HepA (Arkansas, Puerto Rico). Coverage was higher in the during-pandemic period for 29 additional vaccine/jurisdiction combination estimates. At 19 months (Table 3d), during-pandemic coverage was lower than pre-pandemic coverage for 28 vaccine/jurisdiction combinations, including: ≥4 doses of DTaP (New Hampshire, New York, New York excluding New York City, District of Columbia, South Dakota, and Puerto Rico); ≥3 doses of poliovirus vaccine (Puerto Rico); ≥1 dose of MMR (Puerto Rico); Hib-FS (HHS Region 1, Massachusetts, New Hampshire, HHS Region 2, New York, New York excluding New York City, West Virginia, South Dakota, and Puerto Rico); ≥1 dose of VAR (Puerto Rico); ≥4 doses of PCV (New Hampshire, HHS Region 2, and Puerto Rico); ≥1 dose of HepA (Hawaii, Puerto Rico); and the combined 7-vaccine series (New York, New York excluding New York City, West Virginia, South Dakota, and Puerto Rico). An additional 43 coverage estimates were higher in the during-pandemic period compared with the pre-pandemic period. At the 24-month milestone (Table 3e), 16 coverage estimates were lower in the pandemic period, including: ≥4 doses of DTaP (New Hampshire, Puerto Rico); ≥3 doses poliovirus vaccine (Puerto Rico, Illinois excluding Chicago); ≥1 dose of MMR (Louisiana); Hib-FS (New York, West Virginia, Nebraska, and Puerto Rico); ≥3 doses of HepB (New Hampshire); ≥4 PCV (Puerto Rico); ≥1 dose of HepA (Maryland); ≥2 doses of HepA (HHS Region 1); and the combined 7-vaccine series (West Virginia, HHS Region 5, and Puerto Rico). An additional 52 coverage estimates were higher in the pandemic period than in the pre-pandemic period.

Vaccination Coverage for Pre-Pandemic and During Pandemic Cohorts, by Sociodemographic Characteristics

Tables 4 (a-e) provide national aggregate pre-pandemic and during-pandemic coverage estimates for milestone ages (8, 13, 16, 19, and 24 months), stratified by sociodemographic factors race/ethnicity, poverty status, health insurance status, and Metropolitan Statistical Area (MSA) status. At the 8-month milestone (Table 4a), coverage with Hib-PS decreased in the during-pandemic period for non-Hispanic White children and those with private health insurance. During-pandemic coverage with ≥3 doses of DTaP, ≥3 doses of PCV, and rotavirus was higher than pre-pandemic coverage among Hispanic children. HepB birth dose coverage was higher in the during-pandemic period among children of multiple races. At 13 and 16 months (Table 4b, Table 4c), there was no evidence of a decrease in coverage during the pandemic for any of the combinations of vaccines and sociodemographic factors. Coverage with several vaccines increased during the pandemic period, including coverage with ≥1 dose of MMR among privately insured children (13 months), ≥3 doses of HepB among American Indian/Alaska Native children (13 and 16 months), children living at or above poverty (13 and 16 months), and Hispanic children (16 months). At 19 months (Table 4d), coverage with Hib-FS decreased during the pandemic period for children living at or above poverty. Coverage increased during the pandemic period for seven other vaccine/sociodemographic factor combinations, including ≥3 doses of poliovirus vaccine among children living at or above poverty, children with private health insurance, and children living in a non-principal city of an MSA; ≥3 doses of HepB among children living at or above poverty; ≥1 dose of VAR among children with unknown poverty status; ≥4 doses of PCV among Hispanic children; and ≥1 dose of HepA among children with unknown poverty status. At 24 months (Table 4e), a drop in coverage with the combined 7-vaccine series during the pandemic period was seen for Native Hawaiian children, children living below poverty, and children living in non-MSA areas. In contrast, coverage was higher during the pandemic period for 34 combinations of vaccines and sociodemographic factors. Nearly half of these involved ≥1 dose of HepA or ≥2 doses of influenza.

Limitations

The findings in this report are subject to several limitations. (2) The low household survey response rate in the NIS-Child (23% in 2021) and the requirement that only children with adequate provider data (at least one vaccination reported by a health care provider or evidence of having received no vaccinations) are included in analyses create the potential for selection bias if nonrespondents and respondents differ in ways related to immunization coverage. Additionally, although the data are weighted to account for nonresponse and phoneless households, application of weights may not eliminate all bias. Coverage estimates could also be incorrect if some vaccination providers did not return questionnaires or if administered vaccines were not documented accurately. A total survey error assessment conducted using data from 2021 concluded that coverage estimates in the NIS-Child for ≥4 doses of DTaP, ≥1 dose of MMR, the HepB birth dose, and the combined 7-vaccine series underestimate true coverage by 3-9 percentage points (www.cdc.gov/vaccines/imz-managers/nis/downloads/NIS-PUF21-DUG.pdf). When stratified by jurisdiction, a substantial number of during-pandemic estimates were associated with wide confidence intervals (≥20 units), indicating that these coverage estimates are less reliable. This report contains a large number of estimated differences and corresponding statistical test results, making it susceptible to the problem of multiple comparisons. (3) Since each test is associated with some degree of uncertainty, performing multiple statistical tests increases the likelihood of drawing an incorrect conclusion from one or more of them. Finally, the sample size of children born during the pandemic was limited, with the most recent births in May 2020; additional sample for 2020 births will be available with the 2022 NIS-Child data.

Discussion

The COVID-19 pandemic has disrupted distribution and administration of routine childhood vaccines both in the United States and in other countries. (4, 5) Decreases in both vaccine ordering and administration have been documented in the U.S., including substantial declines in doses of DTaP and MMR administered to children aged 0-23 months during March-September 2020 compared with the same period in 2019. (6) Similar decreases in coverage were observed in other data sources. (7) A study assessing vaccine uptake and coverage in a large cohort of children aged 0-18 years found marked declines in routine vaccine uptake in all children between June and August of 2020 compared with the same period in 2019, with a rebound in children 0 to 23 months. (8).

This report using NIS-Child data did not identify any consistent or persistent decline in vaccination coverage associated with the COVID-19 pandemic nationally among all children when comparing those who reached milestone ages prior to the pandemic to those reaching the same ages during the pandemic. Declines were seen for certain subgroups, however. For example, coverage with the combined 7-vaccine series by age 24 months decreased 4-5 percentage points among children living below poverty or in rural areas. There were transient declines in MMR and varicella vaccine coverage at age 13 months among children turning 13 months in March-April 2020, but coverage caught up for these birth cohorts at later ages, and for subsequent monthly birth cohorts at age 13 months. Additionally, for a number of vaccine/milestone age combinations, increasing trends in coverage during the pre-pandemic period were followed by no trends in the during-pandemic period. This was most apparent in the younger age groups, e.g. children reaching 8, 13, or 16 months of age (Table 2 a-e), and could indicate that disruptions in care due to the pandemic muted trends that would have continued in absence of the pandemic. Analyses by jurisdiction revealed just as many, if not more, areas where coverage increased rather than decreased in the during-pandemic period.

The 2022 NIS-Child will include data from more children born shortly before or during the COVID-19 pandemic, providing a more complete assessment of trends in vaccination coverage during the pandemic. In the meantime, efforts should be made to help children catch up on any missed vaccinations. Healthcare providers should review children’s histories and recommend needed vaccinations during every clinical encounter. Resources to help promote and discuss vaccination with parents and guardians can be found at /www.cdc.gov/vaccines/hcp/patient-ed/index.html. Additional routine vaccination catch-up strategies and resources can be found at www.cdc.gov/vaccines/partners/routine-immunizations-lets-rise.html.

Abbreviations: DTaP = diphtheria, tetanus toxoids, and acellular pertussis vaccine; FS = full series; HepA = hepatitis A vaccine; HepB = hepatitis B vaccine; HHS = Health and Human Services; Hib = Haemophilus influenzae type b conjugate vaccine; MMR = measles, mumps, and rubella vaccine; MSA = Metropolitan Statistical Area; PCV = pneumococcal conjugate vaccine; PS = primary series; VAR = varicella vaccine.

Authors

Holly A. Hill, MD, PhD, David Yankey, PhD, James A. Singleton, PhD, Laurie Elam-Evans, PhD, Immunization Services Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention

References

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