Although vaccines are the most powerful tools we have to prevent infections and safeguard public health, their ultimate success relies on popular belief in their efficacy and widespread trust of health recommendations. Unfortunately, vaccine hesitancy—doubt or indecision that may result in delaying or refusing vaccination—is increasing globally and has been identified as one of the top ten threats to global health by the World Health Organization as herd immunity to vaccine-preventable diseases is decreasing in healthy populations.
This poses a risk to people with weakened immune systems such as patients who undergo hematopoietic cell transplants (HCTs), who are thirty times more likely to acquire a vaccine-preventable disease than the general population. The pre-transplantation regimen to deplete patients’ immune systems also wipes out pre-existing immune memory from childhood vaccines. Although most current guidelines recommend revaccination to restore immunity, some studies have found that only 32-67% of patients complete revaccination.
Even with these low rates of revaccination uptake and overall growing controversy over vaccines, the rates of post-HCT vaccine hesitancy have not been well studied. A recent publication in Vaccine investigated how attitudes towards vaccines influence whether HCT survivors choose to revaccinate, and what factors influence these attitudes. Dr. Mihkai Wickline, lead author on the paper, was a former long-time Fred Hutch clinical nurse with the Long-Term Follow-Up (LTFU) Group who now teaches at the UW School of Nursing. During her work with LTFU, she fielded many questions from patients and their providers about revaccination. “As clinicians, we encounter vaccine resistance and hesitancy among the HCT survivors we care for, so we knew HCT survivors were not immune to vaccine hesitancy,” she explains.
To better understand survivors’ attitudes towards vaccination, Dr. Wickline and colleagues developed a mixed-methods survey to gather quantitative and qualitative data from former Fred Hutch transplant patients. They adapted the Vaccination Confidence Scale to measure overall vaccine confidence which has three constructs: how participants view the benefits vaccines provide, whether they are concerned about potential vaccine harms, and how much trust they have in institutions promoting and providing vaccines. Qualitative data was collected by open-ended questions, and answers were assigned a code of “vaccine hesitant,” “mixed confidence,” or “vaccine confident” based on overall impression of the response to compare with the quantitative scale cut-points of low, medium, and high vaccine confidence. Additionally, the authors used thematic analysis to create themes from all the open-ended data.
Over 300 adult HCT survivors in the LTFU cohort—representing all geographic regions of the United States—responded to the survey. Most respondents (70%) had high confidence in vaccines, and many (63%) had completed their revaccination series. Factors that significantly correlated with vaccine confidence were pre-HCT adult vaccine status, ability to pay for vaccines out of pocket, residence in a zip code that voted predominantly Democratic in 2020, and uptake of the COVID-19 vaccine.
A surprising finding was that, of the patients who expressed low confidence in vaccines (11.4%), few outright declined (4%) or planned to avoid (10%) revaccination altogether. This discrepancy between attitude and behavior indicates that high-risk patients may overcome their hesitancy through their own risk analyses or because of trust built through long-term relationships with health care providers.
Many open-ended responses expressed concerns over vaccine safety and efficacy due to immunosuppression and their unique recovery after transplant. As cancer patients and the immunocompromised are often excluded from clinical trials, these responses underscore that HCT survivors are a unique clinical population with their own reservations and hesitancies around vaccination.
“The most pressing question this study raises is, what interventions will be helpful to support vaccine hesitant survivors as they make decisions about revaccination?” Wickline asks. “Will interventions for vaccine hesitancy tested in other populations work for HCT survivors?”
Wickline points out that one evidence-based strategy called bundling—where healthcare providers recommend getting all vaccines for which the patient may be eligible for at once—may not be effective to increase revaccination uptake in this population. This is because some vaccines were less well accepted than others in this study. “Many participants expressed acceptance of childhood vaccines but hesitancy with flu and COVID-19 vaccines. It may be that trying to bundle flu and COVID-19 vaccines will sour acceptance of all the vaccines being offered,” she cautions.
Vaccine hesitancy is not new—since vaccines were first invented, people have been reluctant to use them for any number of reasons. This study is an important step towards understanding those reasons in a uniquely vulnerable population, and to opening dialogues between vaccine hesitant patients and the healthcare profession.
The spotlighted research was funded by the University of Washington School of Nursing and the Oncology Nursing Foundation.
Fred Hutch/University of Washington/Seattle Children’s Cancer Consortium members Drs. Paul Carpenter, Jefferey Harris, Kerryn Reding, Stephanie Lee, Rachel Salit, Masumi Ueda Oshima, and Phuong Vo contributed to this research.
Wickline, M. M., Carpenter, P. A., Harris, J. R., Iribarren, S. J., Reding, K. W., Pike, K. C., Lee, S. J., Salit, R. B., Oshima, M. U., Vo, P. T., & Berry, D. L. (2024). Vaccine hesitancy and routine revaccination among adult HCT survivors in the United States: A convergent mixed methods analysis. Vaccine, 42(26). https://doi.org/10.1016/j.vaccine.2024.126374
Hannah Lewis is a postdoctoral research fellow with Jim Boonyaratanakornkit’s group in the Vaccine and Infectious Disease Division (VIDD). She is developing screens to find rare B cells that produce protective antibodies against human herpesviruses. She obtained her PhD in molecular and cellular biology from the University of Washington.
For the Media