As the COVID-19 pandemic reached the United States in early 2020, there was a vast shift in the daily activities of Americans. Many feared leaving the house, people were quarantining their groceries before eating, and business as usual was disrupted for nearly every sector. As part of this disruption to the norm, routine healthcare visits were neglected.
In Pennsylvania, vaccine clinics and pediatric providers completely or temporarily cancelled appointments in the initial months of the pandemic. According to a recent statewide study, more than three quarters of providers reported closing at some point during the pandemic resulting in thousands of missed routine childhood check-ups. National studies showed large declines in the amount of routine childhood and adolescent vaccines that primary care providers were ordering and administering to patients in the first few months of the pandemic. The decrease in national vaccines rates raised alarm bells to infectious disease and public health experts across the country.
When vaccine rates decrease past a certain threshold—called the herd immunity threshold—outbreaks of these diseases can occur. Herd immunity thresholds are levels of vaccine rates in which so many people in a community are immune to a disease, that the disease has a hard time spreading from person to person. When the herd immunity threshold is reached, everyone in the community is protected, even those of us who cannot get vaccinated for any number of reasons.
With the understanding of how decreases in vaccine rates impact herd immunity and the chances of disease outbreak, the Pennsylvania Immunization Coalition investigated changes in routine childhood and adolescent vaccine rates from before the pandemic and into the present school year. This analysis was compiled into a report—Routine Childhood and Adolescent Immunization Rates by Pennsylvania County 2018-2021—that aimed to analyze if Pennsylvania or any of its counties are vulnerable to preventable disease outbreaks related to decreased vaccine rates.
To accomplish this, we used Pennsylvania State Immunization Law Report (SILR) data which is publicly available through the Pennsylvania State Department of Health (PADOH). This data includes vaccine compliance rates and vaccine waiver rates for each county. The vaccines monitored through this report include measles, mumps, and rubella (MMR); polio; chickenpox (Varicella); hepatitis B; diphtheria, tetanus, and pertussis (Dtap/DTP/DT); tetanus, diphtheria, and pertussis (Tdap/Td); and meningococcal disease (MCV). Within these seven vaccines reported, five are considered childhood vaccines—MMR, polio, varicella, hepatitis B, Dtap/DTP/DT—because the series of vaccines are recommended to be administered by age 6. The remaining two vaccines—Tdap/Td and MCV—are considered adolescent vaccines since the first dose of each series is recommended at 10-11 years of age.
To visualize changes in vaccine rates of childhood and adolescent vaccines, we plotted line plots of the state level rates from the 2018-2019, 2019-2020, and 2020-2021 school years.
By looking at this line plot, we see that on a state level for children under 18, there was a less than 1% decrease in Dtap/DTP/DT, HepB, MMR, and Polio and there was even a slight increase in Varicella vaccine rates over the three-year period. When we looked at the two adolescent vaccines—broken down by grade to capture which dose in the two dose series students were at—the trend was quite different.
Apart from 12th Grade Tdap/Td second dose, each of the adolescent vaccines by appropriate age group showed a larger decline. The other three vaccine rates measured here showed a decline of approximately 4%. Although this may not seem like a large decline, it means that upwards of 10,000 students have missed their vaccine doses during the COVID-19 pandemic. If the missed doses are not evenly spread out across all 67 counties, then some areas are at risk of disease outbreak on account of having lower vaccine rates than that of the state.
In addition to analyzing the state level changes to vaccine rates, the report also investigated county level data to show differences across Pennsylvania. We mapped the vaccine rates for each vaccines reported in the SILR in the 2020-2021 school year. When we looked at the 7th Grade Tdap/Td vaccine rates by county, we observed a lot of variation across the state.
Based on the line plot of the statewide Tdap/Td vaccine rate for 7th Graders, the 2020-2021 rate was just above 90%. However, by mapping the county level vaccine rates for the same vaccine and grade, we saw that some counties had below 80% of their 7th Graders vaccinated for Tdap/Td. One of the diseases the Tdap/Td vaccine protects against is pertussis, otherwise known as whooping cough. Whooping cough is very contagious illness that effects primarily children. According to a report by the PADOH, there were over 2000 cases of whooping cough in Pennsylvania from 2017-2019. The prevalence of whooping cough in Pennsylvania along with the very low rates of Tdap/Td of 7th Graders in some counties underscores the importance of considering vaccine rates by county in addition to as a state.
A similar and more comprehensive analysis was done for each of the vaccines reported in SILR by Pennsylvania county and is included in the report. The SILR data we used are not necessarily a representative iteration of vaccine rates in Pennsylvania seeing as student enrollment varied greatly during the pandemic and that children with vaccine waivers are not included in the calculation for vaccine rates—both of which may slightly skew the data presented.
Despite these limitations to this study, we found that comparison to national trends, Pennsylvania experienced a much smaller decrease in routine vaccine rates; the largest declines in rates occurred in the adolescent vaccines; and that non-medical vaccine exemption rates were highest in the many of the counties with the lowest vaccine rates. This report can be used to inform vaccine programing as we move forward into the follow school years and suggests that there is a need for providing vaccine support to counties with low routine childhood and adolescent vaccine rates and vaccine support for adolescent vaccines across the state.
To read the full report, keep an eye on the PAIC website in the coming months.
This blog was written by Cait McCrory, a PA-AAP/PAIC intern. Cait spearheaded the analysis and writing of the Routine Childhood and Adolescent Immunization Rates by Pennsylvania County 2018-2021. Cait will earn her MPH from the University of Pennsylvania in May 2022 and continue to do vaccine and infectious disease work in her home state of Wisconsin as part of the Wisconsin Population Health Service Fellowship.