Late 2024 saw several reports from the U.S. Centers for Disease Control and Prevention (CDC) and news media detailing observations that childhood vaccination rates are dropping.[1][2][3]The studies being quoted consider very short time periods. One CDC report compares two-year-old child vaccination rates between the 2018-2019 period and 2020-2021, and two other articles consider CDC data on kindergartner vaccination rates in the 2023-2024 school year against the previous school year and 2019-2020.[4][5][6]
These issues beg the question of whether there is an increase in vaccination hesitancy driving the data in the studies, and whether studies of such limited time represent vaccination trends generally. We delve into the question of whether there is truly a reduction in vaccination rates. To gain perspective on the issue, we explore childhood vaccination rates in the United States and Canada through a broader time range than the studies and articles we referred to and consider adult vaccination rates against influenza.
We found the vaccination trends to be unclear, with interesting incongruities. Critically, we observed that some observations of reduced vaccination rates may be a result of reporting limitations.
Let us start with a review of the key children’s vaccines under discussion, why these vaccinations occur, what vaccination rates are targeted, and why governmental bodies would monitor vaccination levels so closely.
Vaccination and the principles of justice
Many of the childhood diseases we vaccinate against are life threatening and should obviously be avoided. This is why childhood vaccination is so common. Childhood vaccines include the measles, mumps, and rubella (MMR) vaccine, the diphtheria, tetanus, and pertussis (DTaP) vaccine, and the polio vaccine. In our article, Analysis of COVID vaccine AEFIs, Part I, we showed the incidences of severe outcomes from a number of these diseases. Measles can cause immunity amnesia (loss of immunity to other diseases), encephalitis, pneumonia, and even death. Tetanus can kill, and polio can kill or paralyze those most affected by it. Varicella, or chicken pox, is fatal in rare instances and leaves the potential of shingles later in life.
The vaccines mentioned above are widely considered safe based on the statistics concerning their potential adverse affects. Readers who are curious will find the ratio of severe outcomes from the disease versus the vaccine (known as the risk ratio) in this same article, Analysis of COVID vaccine AEFIs, Part I. A high ratio suggests high value in receiving an effective vaccine. In the cases of the diseases (and their vaccines) mentioned above, the risk ratios are typically over 1,000, and for some of the vaccines over 100,000.
In our July 27, 2021 article Examining the effectiveness of restrictions and the path to COVID eradication, we showed that to reach herd immunity, polio requires high immunization rates – in the 80% range – and measles requires even higher rates of about 90%. These high vaccination rate requirements, and the potential consequences of an outbreak of a disease such as polio or the measles, motivate governments and health bodies to set high childhood vaccination targets (typically 95%) and to monitor them closely.
Health officials also monitor a key element of bioethics. In our article Mounting COVID frustration is no reason to abandon fundamental principles, we spoke about the four principles of bioethics. While the main topic of that article was the principle of autonomy, concerns over regional or ethnic variations in vaccination rates relate to the principle of justice. Justice is concerned with the equal or fair distribution of resources – vaccines, in this case – and whether people belonging to groups with lower vaccination rates have reasonable access to the treatments.
The reports we mentioned earlier focus on a narrow timeframe, which may be inadvisable from a statistical perspective. Trends cannot be drawn reliably from comparing such short periods. However, the goal of fair treatment in vaccine distribution motivates this approach and makes it understandable despite its scientific limitations.
These are rational and supportable reasons for health officials to monitor vaccination rates closely, though the level and granularity of such study will not concern most of the public in the same way. Most people simply want to know if the vaccines are safe, effective, and if vaccination rates are high enough to prevent the outbreak of serious diseases.
How we get to the bottom of the question
Trends are understood with the highest certainty when sufficient data is collected, which means after a program of vaccinations has occurred. For childhood vaccination of MMR, polio and DtaP, this typically takes two years, though the programs may vary, for example, on a state level in the United States and a provincial level in Canada. In keeping with this schedule, the U.S. and Canada survey vaccination rates of 2-year-old children. This period has the consequence that data on childhood vaccinations is backward looking; the decisions to vaccinate a two-year-old child have occurred over the two previous years.
Surveys on the vaccination rates of kindergarten children, as is done in the United States, will be even further backward looking: the decisions to vaccinate these children may have started as much as five years before the survey year. This means that kindergarten child vaccination data from 2023 is affected by decisions made as early as 2018, which predates COVID-19.
To mitigate this time-lag in vaccination trend analysis, we look at the adult influenza vaccination rates on a yearly basis in the U.S. and Canada. This data concerns a different demographic of the population, but they are more up to date, and involve single, yearly, data points. Influenza vaccination rates should be considered a complementary dataset.
Vaccination-rate data is not generally absolute; these datasets are typically estimates derived from surveys. Sometimes the data arises from state or provincial vaccination reports rather than surveys, but in the U.S. the reporting is a state responsibility, and the methodology varies.
Vaccination rates for kindergarten children in the United States
Every year, each state reports the vaccination status of children enrolled in kindergarten in both public and private schools. The CDC hosts this data online under the name SchoolVax. The reporting is not guaranteed to be consistent everywhere – it can be applied for every student or for groups of students within the state. This data does not typically include homeschooled students.[7]
Figure 1 shows vaccination data from this reporting, focusing on the DTaP, MMR, and polio vaccines for the 2011-2012 to 2023-2024 years.[8]There is a step-decrease, and a negative trend in vaccination rates after the 2019-2020 year. The change at 2019-2020 is notable because this was the period in which COVID-19 first appeared, and readers may wonder if the COVID pandemic influenced vaccination rates and behaviours. This is possible, but, as noted above, most of these vaccinations occur several years prior to enrollment in kindergarten, and the decisions to vaccinate would have been made in earlier years. This means that at least some of the reduced vaccination rate in 2020-2021 could have been a result of decisions made as far back as 2015.
At the very least, this data has a confounding factor. The reduction in observed vaccination rates is meaningful, but U.S. vaccination rates for these diseases remains above 90%.
Figure 1 – Vaccination rates for DTaP, MMR and polio for kindergarten students in the United States.[9]
Vaccination rates for two-year-old children in the United States
The vaccination data for younger children in the United States does not rely on state-level reporting. Instead, it uses a group of phone surveys every year, called the National Immunization Surveys (NIS).[10]These surveys typically include 10,000 to 15,000 respondents nationwide. The CDC hosts this data online under the name ChildVax. Figure 2 shows the vaccination data from these surveys, focusing on the DTaP, MMR, and polio vaccines for 2011 to 2021.[11]2021 is the most recent year in which data is available.
Maximum vaccine coverage in this period occurred in 2018, and vaccination rates have dropped marginally in the following years. Note that vaccination rates appear lower overall than the kindergarten data from Figure 1, which may partially be a result of the differences in methodology (survey versus reporting), but is likely strongly affected by vaccinations occurring between the two-year-old and kindergarten ages. It is significant that the step-decrease in vaccination rates for kindergarten students in the 2020-2021 and 2021-2022 years are not seen in the data from two-year-olds in the same timeframe. Additional data, which will be available in future years, is needed to understand the significance of these differences.
Figure 2 – Vaccination rates for DTaP, MMR and polio for two-year-old children in the United States.[12]
Incongruous vaccination rates for two-year-old children in Canada
Canada collects vaccination data in several ways, most notably through the childhood National Immunization Coverage Surveys (cNICS). This data has been collected every two years since 1994 and is collected for children of age 2, 7, 14 and 17, though the two-year age group receives most attention. In 2021, the age 2 group had 3,954 samples out of 5,446 in total.[13]Figure 3 shows the results of the cNICS surveys from 2013 to 2021.[14][15][16]Again, the 2021 data is the latest available. The vaccination rate goal of 95% has not been reached, but the trend has been a marginal increase over time.
Figure 3– Vaccination rates for DTaP, MMR and polio for two-year-old children in Canada.[17][18][19]
Another method of estimating vaccination rates is the Standardized Reporting on Vaccination (STARVAX) surveillance system. STARVAX was created to obtain more timely vaccination rate data than the cNICS system we discussed earlier, given concerns that childhood vaccination rates might be dropping.[20]The STARVAX system is relatively new and only includes data from a few regions within Canada. The system is a reported method – not a survey – and uses a standardized form across jurisdictions.[21]Such a system has the potential to be superior to the survey methods used by NICS, but in practice the veracity of this data is limited by several factors, including:[22]
- The data currently only includes Alberta, Saskatchewan, Manitoba, and the Yukon.
- The data comes from a registry that may not be accurate based on who is behind the vaccinating organization as well as the reporting requirements. That is, errors may result from whether the children were vaccinated by family doctors versus public health nurses, and the regional reporting requirements. This likely results in an underestimation of immunization rates.
- Incomplete registration of individuals moving to or from the reporting regions could create errors in the vaccination rates.
The vaccination rates are shown in Figure 4 for 2019 to 2023. They are lower than cNICS reported for the common years of 2019 and 2021 in Figure 3 and show a negative trend that was absent from the cNICS data. We noted the apparent drop in vaccination rates shown in Figure 4 in Lessons from 2024: inevitable complexity, necessary principles, as it is remarkable in appearance. We caution readers about the STARVAX data. It is incongruent with the survey data from cNICS, and while we should not ignore the apparent reduction in vaccination rates, they may be a consequence of limitations in the STARVAX reporting system.
Figure 4 – STARVAX vaccination rates for DTaP and MMR for two-year-old children in Canada. This data is subject to reporting limitations.[23]
Adult influenza vaccination rates in the U.S. and Canada
To complement the childhood vaccination data, adult influenza vaccination rates are assessed here for several reasons:
- The influenza vaccination rate estimates are more current in the U.S. and Canada than the childhood vaccination data.
- Influenza vaccinations take place yearly as a single injection, rather than the multi-injection program of many children’s vaccines, making their uptake a better measure of vaccine acceptance at a single point in time.
- Adults decide on whether children are vaccinated, so observing adult influenza uptake has at least some relevance to vaccine acceptance or hesitancy and might be expected to roughly correlate to childhood vaccination rates.
The U.S. collects nationwide influenza vaccination information through a survey system.[24]Figure 5 shows the results of these surveys from 2015 to 2023.[25]The overall trend for influenza vaccination rates in the U.S. from 2015 through 2023 is slightly increasing over time. The 2020 to 2021 reporting period was a local high, with rates dropping marginally in the next two reporting years.
Given that the two post-COVID-pandemic years follow the local high of 2020 to 2021, it should not be concluded at present that these rates represent a material drop compared to the study period data. In fact, the rate of vaccination for influenza in the 2022-2023 period is higher than the average rate over the period shown.
Figure 5 – Vaccination rates for influenza in adults the United States.[26]
Canadian influenza vaccination rates are also estimated from a nationwide annual survey.[27]Figure 6 shows the results of these surveys from 2015-2016 through the 2023-2024 survey.[28][29][30]There is no measured drop in vaccination after the 2019-2020 or the 2020-2021 surveys; the subsequent years both show higher vaccination rates.
Figure 6 – Vaccination rates for influenza in Canadian adults.[31][32][33]
Interpretation
Readers should be aware that limitations in reporting methods and the backward nature of assessing childhood vaccinations can make interpretation of this data difficult. Reporting and surveying methods vary by region, adding to vaccination-rate trend uncertainty.
Taken together, the vaccination data in the U.S. and Canada is unclear. While some elements of the data support a recent negative trend in vaccination, other elements of the data refute it. Strong influenza vaccination rate trends in adults does not suggest massive widespread vaccine hesitancy, however apparent reduction in two-year-old children’s vaccination rates in the U.S. is noteworthy. The current STARVAX report on Canadian two-year-old child vaccination rates is questionable and should be viewed with skepticism.
Because of the severity of the diseases targeted by the MMR, polio, and DTaP vaccines, and the high vaccination rates required to prevent their outbreak, vigilance in monitoring is advised. Readers should also be aware of the characteristics and limitations of vaccination reporting methods and temper reaction to the data. Readers are advised to consider the entire vaccination datasets and time periods in assessing trends rather than focusing on single-year-to-single-year comparisons as has been done in some news reports.
References
[1] Hill, H., D. Yankey, L.D. Elam-Evans, Y. Mu, M. Chen, G. Peacock, J.A. Singleton, 2024, Decline in Vaccination Coverage by Age 24 Months and Vaccination Inequities Among Children Born in 2020 and 2021 — National Immunization Survey-Child, United States, 2021–2023, MMWR, 73(38), 844-853
[2] Williams, E., J. Kates, November 18, 2024, Childhood Vaccination Rates Continue to Decline as Trump Heads for a Second Term, KFF
[3] The Center for Health Affairs, October 31, 2024, Declining Vaccination Rates and Increasing Disease Outbreaks are a Troubling Trend
[4] Hill, H., D. Yankey, L.D. Elam-Evans, Y. Mu, M. Chen, G. Peacock, J.A. Singleton, 2024, Decline in Vaccination Coverage by Age 24 Months and Vaccination Inequities Among Children Born in 2020 and 2021 — National Immunization Survey-Child, United States, 2021–2023, MMWR, 73(38), 844-853
[5] Williams, E., J. Kates, November 18, 2024, Childhood Vaccination Rates Continue to Decline as Trump Heads for a Second Term, KFF
[6] The Center for Health Affairs, October 31, 2024, Declining Vaccination Rates and Increasing Disease Outbreaks are a Troubling Trend
[7] Centers for Disease Control and Prevention, October 16, 2024, About SchoolVaxView
[8] Centers for Disease Control and Prevention, October 2, 2024, Vaccination Coverage and Exemptions among Kindergartners
[9] Centers for Disease Control and Prevention, October 2, 2024, Vaccination Coverage and Exemptions among Kindergartners
[10] Centers for Disease Control and Prevention, August 20, 2024, About ChildVaxView
[11] Centers for Disease Control and Prevention, August 26, 2024, Vaccination Coverage among Young Children (0 – 35 Months) | ChildVaxView | CDC
[12] Centers for Disease Control and Prevention, August 26, 2024, Vaccination Coverage among Young Children (0 – 35 Months) | ChildVaxView | CDC
[13] Government of Canada, Highlights from the 2021 childhood national Immunization Coverage Survey (cNICS)
[14] Government of Canada, Highlights from the 2021 childhood national Immunization Coverage Survey (cNICS)
[15] Statistics Canada, June 12, 2023, Childhood National Immunization Coverage Survey, 2021
[16] Government of Canada, Vaccination coverage in Canada, Vaccination coverage in Canada – Canada.ca
[17] Government of Canada, Highlights from the 2021 childhood national Immunization Coverage Survey (cNICS)
[18] Statistics Canada, June 12, 2023, Childhood National Immunization Coverage Survey, 2021
[19] Government of Canada, Vaccination coverage in Canada, Vaccination coverage in Canada – Canada.ca
[20] Jeevakanthan, A., S. Roubos, C. Hong, A. Hender, M. Granger, S. Khan, M. Shahid, S. LeBlanc, J. O’Connell, and N. L. Gilbert, June 27, 2024, Routine vaccination coverage at ages 2 and 7, before, during, and after the COVID‑19 pandemic: Results from the STARVAX surveillance system, Canadian Journal of Public Health
[21] Jeevakanthan, A., S. Roubos, C. Hong, A. Hender, M. Granger, S. Khan, M. Shahid, S. LeBlanc, J. O’Connell, and N. L. Gilbert, June 27, 2024, Routine vaccination coverage at ages 2 and 7, before, during, and after the COVID‑19 pandemic: Results from the STARVAX surveillance system, Canadian Journal of Public Health
[22] Jeevakanthan, A., S. Roubos, C. Hong, A. Hender, M. Granger, S. Khan, M. Shahid, S. LeBlanc, J. O’Connell, and N. L. Gilbert, June 27, 2024, Routine vaccination coverage at ages 2 and 7, before, during, and after the COVID‑19 pandemic: Results from the STARVAX surveillance system, Canadian Journal of Public Health
[23] Jeevakanthan, A., S. Roubos, C. Hong, A. Hender, M. Granger, S. Khan, M. Shahid, S. LeBlanc, J. O’Connell, and N. L. Gilbert, June 27, 2024, Routine vaccination coverage at ages 2 and 7, before, during, and after the COVID‑19 pandemic: Results from the STARVAX surveillance system, Canadian Journal of Public Health
[24] Centers for Disease Control and Prevention, September 6, 2024, Flu Vaccination Coverage, United States, 2022–2023 Influenza Season
[25] Centers for Disease Control and Prevention, September 6, 2024, Flu Vaccination Coverage, United States, 2022–2023 Influenza Season
[26] Centers for Disease Control and Prevention, September 6, 2024, Flu Vaccination Coverage, United States, 2022–2023 Influenza Season
[27] Government of Canada, 2016-2017 Seasonal Influenza (Flu) Vaccine Coverage Survey results
[28] Government of Canada, 2016-2017 Seasonal Influenza (Flu) Vaccine Coverage Survey results
[29] Government of Canada, Vaccine uptake in Canadian adults 2019
[30] Government of Canada, Seasonal Influenza Vaccination Coverage in Canada, 2023-2024
[31] Government of Canada, 2016-2017 Seasonal Influenza (Flu) Vaccine Coverage Survey results
[32] Government of Canada, Vaccine uptake in Canadian adults 2019
[33] Government of Canada, Seasonal Influenza Vaccination Coverage in Canada, 2023-2024
