PROmotion of COVID-19 BOOSTer VA(X)Ccination in the Emergency Department - PROBOOSTVAXED

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University of California San Francisco (UCSF)






Behavioral: Vaccine Acceptance Question
Behavioral: Vaccine Messaging

Study type


Funder types



R01AI166967-01 (U.S. NIH Grant/Contract)

Details and patient eligibility


The goal of this cluster randomized clinical trial is to test the efficacy of messaging interventions to increase booster vaccine uptake in adults in the emergency department(ED). The main question[s] and goals of this study are:

  • does the intervention of vaccine messaging increase booster vaccine uptake at 30 days post ED visit?
  • does the intervention of asking about vaccine acceptance increase booster vaccine uptake at 30 days post ED visit?
  • considering recent national changes to funding and availability of updated vaccines, the investigators will examine the effects of these changes on vaccine acceptance and uptake in ED populations. Specifically, they will stratify EDs and ED patients according to the ED availability of vaccines, and they will also examine whether costs and availability of vaccines are a deterrent to patient acceptance and uptake of vaccines

Full description

I. Overview On January 22, 2020, Acting Health and Human Services Secretary Norris Cochran declared COVID-19 a national public health emergency, an action that eventually enabled emergency authorization for free COVID-19 vaccines, testing and treatments. This public health declaration has been renewed seven times for 90-day intervals, as required under section 319 of the Public Health Service (PHS) Act. Under this declaration over the past two years, the US government has provided full support and distribution of COVID-19 vaccines and therapeutics (antibody therapies, remdesivir, and nirmatrelvir/ritonavir), such that they have been widely available and free of charge to all Americans. Although these measures have not, by any means, ended the pandemic, it is clear from multiple epidemiologic modeling studies that they have decreased hospitalizations and saved hundreds of thousands of lives. They have also led to a narrowing of the profound morbidity and mortality disparities gap that was seen in minority populations in the first two waves of the pandemic.

The PROCOVAXED trial was a multicenter study that sought to decrease COVID-19 vaccine hesitancy and increase COVID-19 vaccine uptake through the use of vaccine messaging platforms in the emergency department (ED). In this trial, investigators found that implementation of our COVID-19 messaging platforms (videos, information sheets and scripted, direct messaging) were associated with greater COVID-19 vaccine acceptance and uptake among unvaccinated ED patients (Rodriguez RM, Nichol G, Eucker SA, et al. Effect of COVID-19 Vaccine Messaging Platforms in Emergency Departments on Vaccine Acceptance and Uptake: A Cluster Randomized Clinical Trial. JAMA Intern Med. 2023;183(2):115-123. doi:10.1001/jamainternmed.2022.5909).

In January 2022, the investigators extended PROCOVAXED by shifting the focus to vaccinated ED patients to examine the timely and critically important topic of booster vaccine hesitancy in underserved ED populations. To better characterize COVID-19 booster hesitancy, the investigators performed a cross-sectional study at five high-volume, safety-net hospital EDs in four cities (San Francisco, Philadelphia, Seattle, and Durham, NC) using survey tools to gather quantitative data on vaccination status, demographic variables, usual source of care, and attitudes toward booster vaccination. Of 771 participants who had completed their full initial series, 316 (41%) had not received any booster vaccine. Among these 316 non-boosted participants, 179 (57%, 95% CI 51-62) stated they would decline or were unsure whether they would accept a booster vaccine if it was offered to them (i.e., booster-hesitant). Investigators found the following associations with booster vaccine hesitancy: age 35-49 years vs age 18-34 years (OR 1.16, 95% CI 0.99-1.36); Asian vs White race (OR 0.21, 95% CI 0.05-0.93); Hispanic/Latino vs White ethnicity (OR 1.59, 95% CI 0.82-3.09); primary language non-English vs English (OR 2.35, 95% CI 1.49-3.71); and Republican vs Democrat party affiliation (OR 6.07, 95% CI 4.21-8.75). The three most common reasons for booster vaccine hesitancy were a preference to wait for more information (25%), concerns about side effects and safety (24%), and "I don't need one because I'm fully vaccinated" (20%).

Recognizing the ED as a unique opportunity to address COVID-19 booster vaccine hesitancy in underserved populations, the investigators will launch the PROmotion of COVID-19 BOOSTer VA(X)ccination in the Emergency Department (PROBOOSTVAXED) trial as an extension of the PROCOVAXED trial, seeking to increase COVID-19 booster vaccine acceptance and uptake among vaccinated ED patients. Because of Omicron variant-associated surges during the COVID-19 pandemic with corresponding research staff illness and ED overcrowding, the investigators found wide week-to-week fluctuations in enrollment in the PROCOVAXED study. To reduce this variability of enrollment, the investigators have changed the unit of randomization from 1-week to 1-day in the PROBOOSTVAXED trial.

As of May 11, 2023, the COVID-19 public health emergency ended. Consequently, not only are the costs for vaccines, testing, and treatments shifted to health insurers and patients via commercial payment mechanisms, but COVID-19 vaccines are no longer available in some EDs. Since our research focuses on the delivery and availability of vaccines to underserved populations whose only health care access occurs in EDs, the team believes that this represents a potential barrier to 30-day vaccine uptake in these populations. The investigators have been informed that only some of the PROBOOSTVAXED study sites will have COVID-19 vaccines available for distribution in the ED, and this availability is subject to change throughout the study period. Nevertheless, the team will proceed with the same research protocol, however, the investigators feel it is important to examine how ED vaccine availability will affect 30-day vaccine uptake in underserved populations. They will therefore be performing additional subgroup analyses that compare 30-day vaccine uptake among sites with available COVID-19 vaccine to those without for the intervention and control arms.They will also evaluate whether patient costs of vaccines are a deterrent to acceptance and uptake.

While the sample size calculation for this research is derived from Aim 1, the investigators emphasize that this is a pragmatic study in which they seek to evaluate the fluid real-world changes in COVID-19 vaccine availability and funding. As stated above, there have been (and likely will continue to be) changes in payment for and availability of vaccines in EDs.

The investigators therefore have developed our protocol and aims below to assess the impact of these changes.

Aim1: To determine whether implementation of COVID-19 booster vaccine trusted messaging platforms is associated with increased booster vaccine uptake in ED patients. At five EDs (Zuckerberg San Francisco General, UCSF Parnassus Medical Center [San Francisco, CA], Thomas Jefferson University Hospital [Philadelphia, PA], Ben Taub Hospital [Houston, TX], Duke University Medical Center [Durham, NC]), investigators will conduct a cluster-randomized controlled trial of the implementation of PROBOOSTVAXED trusted messaging platforms, with 30-day booster vaccine uptake as the primary outcome and booster vaccine uptake in the ED as a secondary outcome. Hypothesis: Implementation of PROBOOSTVAXED trusted messaging platforms in EDs will be associated with increased 30-day booster vaccine uptake in vaccinated ED patients.

Aim 1a: To determine whether implementation of COVID-19 booster vaccine trusted messaging platforms in EDs is associated with increased booster vaccine acceptance in ED patients. For this aim, booster vaccine acceptance in the ED assessed via ED survey will be the primary outcome. Hypothesis: Implementation of PROBOOSTVAXED trusted messaging platforms in EDs will be associated with increased booster vaccine acceptance in ED patients.

Aim 2: To determine whether implementation of a protocol in which ED patients are asked whether they will accept a COVID-19 booster vaccine in the ED is associated with increased booster vaccine uptake in ED patients. Hypothesis: Implementation of an ED protocol in which patients are asked whether they will accept a COVID-19 booster vaccine will be associated with increased 30-day booster vaccine uptake in ED patients.

Aim 3: To compare vaccine uptake (during the index ED visit and 30 days post visit) between sites that have COVID-19 booster vaccine available and those that do not.

Aim 3a: To compare vaccine acceptance and 30-day uptake among patients with health insurance versus those without health insurance (evaluating the effects of patient vaccine cost on acceptance and uptake).

Aim 4: To compare COVID-19 vaccine uptake in this current study with data gathered in our previous COVID-19 vaccine messaging trial.

General Design: This is a three-arm cluster-randomized controlled trial (CRCT).


744 estimated patients




18+ years old


Accepts Healthy Volunteers

Inclusion criteria

  1. Age > 18 years
  2. Presenting to ED
  3. No receipt of COVID-19 booster within prior 6 months
  4. Able to provide informed consent
  5. Fluent in English or Spanish
  6. Anticipated ability to complete study intervention in ED i.e., able to watch a 3-minute videoclip

Exclusion criteria

  1. Major trauma such that it will preclude survey
  2. Inability to participate in a survey because of intoxication, altered mental status, or critical illness
  3. Incarceration
  4. Psychiatric hold
  5. Patients who state that they have already received a bivalent COVID-19 booster vaccine or other COVID-19 vaccine within the prior 6 months
  6. Patients who are in the ED for suspected acute COVID-19

Trial design

Primary purpose

Health Services Research



Interventional model

Parallel Assignment


Single Blind

744 participants in 3 patient groups

PROBOOSTVAXED Intervention M (Messaging + Vaccine Question)
Experimental group
Vaccine messaging Vaccine acceptance question All patients will receive an Intake Survey assessing their demographic and vaccination information. At the end of the Intake Survey, the Clinical Research Coordinator (CRC) will deliver the booster vaccine information flyer and ask the patient if they will watch a short video on booster vaccines. If they agree, the CRC will give them a QR code to view the video on their smartphone or an iPad. After finishing with the video, the CRC will tell the subject that they will be back for the Vaccine Acceptance survey. The CRC will then leave the room and ask the patient's primary provider to deliver the booster vaccine scripted message. This message is short and should not significantly impact provider workflow. Vaccine Acceptance Survey (Post-Intervention) in the ED: We will administer the Vaccine Acceptance Survey at 30 minutes to 3 hours after the Intake Survey.
Behavioral: Vaccine Messaging
Behavioral: Vaccine Acceptance Question
Intervention Q (Vaccine Question, No Messaging)
Active Comparator group
No vaccine messaging Vaccine acceptance question asked in the Vaccine Acceptance Survey Vaccine Acceptance Survey: We will administer the Vaccine Acceptance Survey at some time (generally 30 minutes but up to 3 hours) after the Intake Survey. The surveys in the control group retain the same key primary and secondary outcome questions as in the intervention group Vaccine Acceptance surveys.
Behavioral: Vaccine Acceptance Question
Control (No Messaging, No Vaccine Question)
No Intervention group
No vaccine messaging No vaccine acceptance question The workflow during this arm is identical to the Intervention Q arm except there will be no Vaccine Acceptance Question survey.

Trial contacts and locations



Central trial contact

Melanie Molina, MD; Robert Rodriguez, MD

Data sourced from

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