Understanding and Addressing the Disparity in Vaccination Coverage Among U.S. Adolescents Living in Rural Versus Urban Areas
Phase: NA
Conditions: COVID-19 Vaccines
Sponsor: Marshfield Clinic Research Foundation

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PROTOCOL NAME 
COVID-19 Booster Dose Reminder/Recall for Adolescents 
 
 
 
VERSION 
Version 1.0 
 
 

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TABLE OF CONTENTS 
I. 
PROTOCOL SYNOPSIS .............................................................................................................. 4 
II. 
BACKGROUND ......................................................................................................................... 5 
A. Marshfield Clinic Health System ........................................................................................... 6 
III. STUDY OBJECTIVE .................................................................................................................... 6 
IV. STUDY POPULATION ................................................................................................................ 6 
A. Inclusion Criteria ................................................................................................................... 6 
B. Exclusion Criteria .................................................................................................................. 6 
V. 
INTERVENTION PERIOD ........................................................................................................... 7 
VI. INTERVENTION ........................................................................................................................ 7 
A. Randomization...................................................................................................................... 7 
VII. OUTCOME MEASURES ............................................................................................................. 7 
A.  Primary Endpoint ................................................................................................................... 7 
VIII. PLANNED ANALYSIS ................................................................................................................. 7 
A.  Sample Size and Power .......................................................................................................... 8 
IX. HUMAN SUBJECTS CONSIDERATIONS ..................................................................................... 8 
X. 
REFERENCES ............................................................................................................................ 8 
XI. APPENDIX ................................................................................................................................ 9 
 
 
 
 
 
 
 
 
 
 
 
 

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LIST OF ABBREVIATIONS 
Abbreviation or Term  
Definition  
CDC  
Centers for Disease Control and Prevention  
HIPAA 
Health Insurance Portability and Accountability Act 
HPV 
Human Papillomavirus 
MCHS 
Marshfield Clinic Health System 
MenACWY 
Meningococcal Conjugate Vaccine 
Tdap 
Tetanus, Diphtheria, and Acellular Pertussis Vaccine 
 
 

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I. 
PROTOCOL SYNOPSIS 
Study Sponsor: Centers for Disease Control and Prevention (CDC) 
Title: COVID-19 Booster Dose Reminder/Recall for Adolescents 
Study Short Name: COVID-19 Booster Reminders 
Study Rationale: Uptake of COVID-19 booster vaccines among adolescents in the United 
States is suboptimal. Booster dose coverage is significantly lower among adolescents aged 12-
17 years relative to older age groups. Patient reminder/recall systems have been shown to be 
an effective strategy to increase vaccination among patients of all ages. 
Study Objective: To assess the efficacy of a one-time reminder/recall for COVID-19 booster 
dose among eligible adolescents in a regional rural healthcare system. 
Study Design: We will conduct a 1:1 randomized intervention by sending a one-time 
reminder/recall notice to parents of 12-17 year-olds due for a COVID-19 booster dose. Those 
randomized to the intervention arm will receive a one-time reminder/recall via their parent’s 
preferred method of communication (mailed letter, text, email) while the usual care (control) 
arm will not receive any reminder/recall notice. This study will be conducted at a single 
integrated healthcare system serving patients in central, northern, and western Wisconsin. 
Endpoint: The primary endpoint will be receipt of COVID-19 booster dose within 90 days of 
randomization. 
Analysis: Analyses will compare receipt of COVID-19 booster dose among adolescents 
assigned to the intervention versus usual care. 
 
 
 

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II. 
BACKGROUND 
To increase protection against SARS-CoV-2 infection, a single COVID-19 booster dose was 
recommended in the United States for adolescents aged 16-17 years in December 2021 and 12-
15 years in January 20221. Uptake of the first COVID-19 booster dose among children and 
adolescents has been suboptimal. As of August 2022, booster dose coverage among 
adolescents aged 12 through 17 years was 33% compared to 70% among adults aged ≥65 
years2. 
Centralized reminder and recall systems have been shown to be a cost-effective strategy to 
increase vaccination rates3. Reminder and recall at Marshfield Clinic Health System (MCHS) are 
centralized and target young children aged 18-23 months and adolescents aged 12 years. In 
accordance with CDC and MCHS vaccination recommendations, COVID-19 vaccine was added to 
the reminder/recall letters for 12-year olds due for tetanus, diphtheria, and acellular pertussis 
vaccine (Tdap), meningococcal conjugate vaccine (MenACWY), or human papillomavirus (HPV) 
vaccine in the summer of 2021.  
Beginning January 2022, individuals aged 12 and older who have completed the primary series 
were eligible to receive COVID-19 boosters1. We propose to assess the efficacy of a one-time 
reminder/recall targeting adolescents aged 12-17 years who are eligible, but have not yet 
received the booster vaccine. 
The intervention will leverage the existing MCHS’s centralized reminder/recall system and 
process for enrolling patients for text and email communication regarding appointments and 
healthcare updates. The proposed intervention is a component of a larger project funded by 
the Centers for Disease Control and Prevention (CDC) to understand and address determinants 
of rural-urban differences in vaccine uptake among adolescents in the upper Midwest 
(NCT05148559).  

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A. Marshfield Clinic Health System 
Marshfield Clinic Health System is a large integrated regional healthcare system that serves a 
predominantly rural population. MCHS has over 10,000 employees working at 55 clinical 
locations throughout central, western, and northern Wisconsin, serving over 18,600 
adolescents aged 12-17 years. The MCHS primary service area encompasses 32 counties in 
Wisconsin, including 70% of the state’s rural counties (Figure 1). 
III. 
STUDY OBJECTIVE 
To assess the efficacy of a one-time reminder/recall for COVID-19 booster dose sent via the 
parent’s preferred method of communication among adolescents aged 12-17 years. 
IV. 
STUDY POPULATION  
The target population is parents of MCHS adolescent patients aged 12-17 years who are due for 
a COVID-19 booster dose. Booster eligible patients were those who completed the COVID-19 
primary series, defined as receipt of 2 doses of Pfizer/BioNTech mRNA vaccine ≥17 days apart, 
and were due for the COVID-19 booster (i.e., ≥5 months since their second dose). Inclusion and 
exclusion criteria are outlined below. 
A. Inclusion Criteria 
• Marshfield Clinic Health System patient aged 12-17 years with at least one 
preventive visit or two evaluation & management visits with a MCHS provider in 
the last 36 months 
• Due for at COVID-19 booster dose (completed the COVID-19 primary series and it 
has been ≥5 months after the second dose) 
Figure 1. Marshfield Clinic Health System Service Area and Rural/Urban Classification of Counties based on 
Urban Influence Codes 
USDA ERS - Urban Influence Codes 
 

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B. Exclusion Criteria 
• Primary care provider is not affiliated with MCHS 
• Opted out of MCHS’s centralized vaccine reminder notifications 
• Received COVID-19 vaccine off label 
• Missing or invalid contact information 
• Deceased 
V. 
INTERVENTION PERIOD 
The intervention will be conducted in Spring 2022, as soon as possible after IRB approval is 
obtained.  
VI. 
INTERVENTION 
The intervention (reminder/recall) consisted of a one-time booster dose reminder sent to 
parents using their specified preferred communication method (postal mail, email, or text). The 
default preferred communication method will be postal mail (letter) if text or email is not 
specified in the electronic health record. The reminder/recall message will differ for those who 
will receive text versus letter or email, due to restrictions on privacy and length of text 
messages (APPENDIX). The usual care group will not receive the reminder/recall until after the 
90-day evaluation period. All persons in the usual care group will receive the reminder/recall 
via mailed letter. 
A. Randomization 
Eligible adolescents will be stratified based on communication method and rurality (using home 
address). Each patient who is eligible at the time of data extraction/randomization will be 
assigned a random number, which will be used to facilitate stratified random sampling. Within 
each strata, the random number will be used to assign patients to intervention (reminder/recall 
sent via postal mail, text or email) or usual care (no reminder/recall) arm in a 1:1 ratio.  
VII. 
OUTCOME MEASURES 
A.  Primary Endpoint 
The primary endpoint will be documentation of receipt of a COVID-19 booster dose during the 
90 days after randomization (90-day evaluation period). 
Receipt of COVID-19 booster dose will be obtained from data available from the MCHS 
electronic health data, which includes a local vaccination registry that exchanges vaccination 
data from the state immunization registry. 
VIII. 
PLANNED ANALYSIS 
Data will be analyzed using the data analysis software, SAS. We will calculate the absolute 
difference in COVID-19 booster dose receipt between study groups, as well as confidence 
intervals. We will also assess differences between arms using Chi-square tests, Student’s t-test 
and Wilcoxon rank sum test where appropriate. 

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A.  Sample Size and Power 
This was a system-wide initiative with the intention that all eligible adolescent patients receive 
the reminder/recall. Therefore, power calculations were not done. We estimate about 18,600 
MCHS adolescent patients aged 12-17 years, of whom, 25% or about 4,650 have completed the 
COVID-19 primary series and may be due for the booster dose.  
IX. 
HUMAN SUBJECTS CONSIDERATIONS 
This is a quality improvement initiative aimed at measuring the impact of a focused 
intervention to improve adolescent vaccination rates. Potential risks are limited to the 
possibility that participants’ identifying information would be inadvertently disclosed. We do 
not anticipate any major risk to participants hence, a waiver of informed consent and HIPAA 
authorization have been requested and approved by the MCHS Institutional Review Board. 
 
X. 
REFERENCES 
1. Centers for Disease Control and Prevention. (2022, January 5). CDC expands booster 
shot eligibility and strengthens recommendations for 12-17 year olds. Centers for 
Disease Control and Prevention. Retrieved September 15, 2022, from 
https://www.cdc.gov/media/releases/2022/s0105-Booster-Shot.html  
2. Fast, H. E., Murthy, B. P., Zell, E., Meng, L., Murthy, N., Saelee, R., . . . Harris, L. (2022). 
Booster COVID-19 Vaccinations Among Persons Aged >/=5 Years and Second Booster 
COVID-19 Vaccinations Among Persons Aged >/=50 Years - United States, August 13, 
2021-August 5, 2022. MMWR Morb Mortal Wkly Rep, 71(35), 1121-1125. 
doi:10.15585/mmwr.mm7135a4 
3. Singer, E., & Couper, M. P. (2008). Do incentives exert undue influence on survey 
participation? Experimental evidence. J Empir Res Hum Res Ethics, 3(3), 49-56. 
doi:10.1525/jer.2008.3.3.49 
 
 
 
 
 

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XI. 
APPENDIX  
Intervention mailed letter/email 
Give your child’s COVID-19 vaccination protection a boost. 
 
Dear Parent or Guardian: 
 
This is a reminder that <<child’s name>> is due for their COVID-19 booster dose.   
 
Everyone ages 12 years and older is recommended to get a booster dose for the best protection 
against COVID-19 and circulating variants. Preteens who are up to date with their COVID-19 
vaccinations and symptom free do not have to miss school or other activities because of 
quarantine after close contact. 
 
Please contact Marshfield Children’s at 877-998-0880 to schedule an appointment today.  To 
self-schedule online, visit https://www.marshfieldclinic.org/covidvaccine. 
 
If <<child’s name>> received COVID-19 vaccine or other vaccines from another provider, please 
let us know so we can update our records. If you need help paying for vaccinations, our Patient 
Assistance Center can help. Please call them at 1-800-782-8581, extension 94475. 
 
Thank you for allowing us to care for <<child’s name>>. 
 
Marshfield Children’s 
 
 
Intervention text message 
From Marshfield Children’s: Everyone ages 12 years and older is recommended to get a booster 
dose for the best protection against COVID-19 and circulating variants. Please call 877-998-0880 
to schedule a booster appointment today. To self-schedule online, visit 
https://www.marshfieldclinic.org/covidvaccine. Please do not reply.