Introduction: The COVID-19 vaccine is an effective measure for preventing and controlling COVID-19 epidemics, and the World Health Organization lists older adults as a high-priority group for COVID-19 vaccination. However, the willingness of older people to be vaccinated against COVID-19 remains an important issue in achieving herd immunity. We investigated the effectiveness of a COVID-19 vaccine intervention for older adults, based on self-determination theory.

Methods and analysis: Questionnaires were administered to assess vaccine willingness at baseline and at 6 weeks following educational intervention programs concerning vaccination against COVID-19. Four nursing homes with a population size of over 100 will be selected and randomized into intervention and control groups. The control group will undergo conventional intervention methods, and the intervention group will undergo a comprehensive intervention program based on self-determination theory.

Ethics and dissemination: The study has been approved by the Ethics Committee of Taizhou Hospital, Zhejiang Province, China (approval number: K20230832).

1. Study design and data collection This class pilot study will be conducted in September 2023 at a nursing home in Taizhou, China. This study has been approved by the Ethics Committee of Taizhou Hospital, Zhejiang Province, China (approval number: K20230832). All procedures will be performed in accordance with the guidelines of our institutional ethics committee and in compliance with the Declaration of Helsinki. The respondents' information will remain anonymous.
2. Patients and public involvement The study participants will be not involved in the design, implementation, or reporting of the study.

2.1 Recruitment 2.2.1 Inclusion criteria

1. 60 years old or above
2. Have not been vaccinated for COVID-19 or have not completed the fourth booster shot of the COVID-19 vaccine
3. Able to communication and willing to participate in the survey voluntarily 2.2.2 Exclusion criteria

(1) People with contraindications to vaccination (2) People with communication disorders (3) Those who do not want to participate in the survey 2.3.3 Grouping of study participants We will select four senior care institutions in Taizhou City with a population of 100 or more residents. We will divide them into intervention and control groups.

2.4 Sample size The sample size was determined using G*Power software v3.1.9.2 (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany). It will be estimated for repeated measures between the two groups at a significance level of 0.05, effect size of 0.19, and power of 95%. The final calculated sample size is 182 participants. Assuming a 10% attrition rate over the course of the intervention, we set a target of recruiting 200 participants. Based on the number of repeated measurements, this represented 100 participants in each group.

2.5 Composition of investigators

1. One master's degree in public health
2. Four master's degrees in infection
3. Two physicians in infectious diseases
4. Two trained locals 2.6 Intervention 2.6.1 Control group: traditional health education In the control group, a conventional intervention will be used, and health education brochures on the COVID-19 vaccine will be distributed for the study participants to read on their own time. The contents of the brochure included basic knowledge concerning the SARS-CoV-2 coronavirus, COVID-19 vaccine, herd immunity, and precautions for vaccination.

2.6.2 Self-determination theory-based health education measures The intervention group received self-determination theory-based interventions, with targeted interventions proposed based on the self-determination theory-including health-related talks and sharing sessions. To ensure that older individuals with varying levels of literacy understood the intervention, the process was conducted in the local native dialect. Health lectures will be conducted to elicit and acknowledge the perspectives and emotions of our cohort of older adults toward vaccination, support their choices and initiatives, and provide a rationale for vaccination-related recommendations while communicating with them to better understand their major barriers toward vaccination. This will be done with the idea of meeting the autonomy and competence needs of our cohort, based on one of the basic premises of self-determination theory. Health-related lectures empower older adults to make autonomous decisions through cognitive reframing . It has been found that successful vaccination planning relies on people acquiring appropriate and adequate health-related knowledge. The three basic psychological needs of older adults will be met through communication and interaction, both with them and with significant members of their lives (e.g., caregivers, family members, doctors, and nurses) during sharing communication sessions. We also will seek to motivate the participants by asking them questions and awarding them gifts during each health lecture and sharing session. Competence needs will be met by developing challenges for our participant cohort . The entire intervention will last 6 weeks, and will be followed by a face-to-face questionnaire.

Inclusion Criteria:

(1) ≥ 60 years of age; (2) had not previously been vaccinated with a COVID-19 vaccine, or had not yet received their fourth booster dose of the vaccine; and (3) had the ability to communicate verbally and volunteered to participate in the survey.

Exclusion Criteria:

(1) contraindications to vaccination; (2) communication disorders; and (3) unwillingness to participate.