Study design and setting
This study used a cross-sectional online survey that was distributed between May 2nd to 20th, 2020, across Iran. Different hypothetical COVID-19 vaccine scenarios were designed using the state-preference WTP method to estimate private vaccine acceptance and demand.
Study population, sampling and sample size
The study population were all Iranians aged more than 18 years old who had access to the internet in all provinces of Iran. We used a mixed sampling process (convenience and snowball sampling). In this way, at the beginning of the survey, a focal point was selected to distribute the questionnaire link in each province. There was not a sampling framework and responses to the questionnaire were completely random. To this end, the link was sent to anyone who could only answer anonymously and/or send it to anyone else; hence, the questionnaire link was sent randomly and distributed in the form of snowballs by the focal points and previous participants. According to Harapan
et al. (
23) study, the sampling adequacy was determined. In addition, an invitation letter and a written consent form that included information about research purposes and ethical issues were provided for the individuals.
Study instrument
The study instrument was a structured questionnaire including three main parts: COVID-19 virus risk assessment, respondents’ characteristics, and WTP for hypothetical COVID-19 vaccines. Before asking questions, updated information about the number of COVID-19 cases, deaths, and recovered ones in Iran was presented to participants with a website link of “world meters coronavirus info” (
24).
Here are the details of each section:
A) Risk assessment
Three questions were designed to assess the risk of coronavirus on a 5-point Likert scale as follows:
How dangerous do you consider corona-virus to be?
How much do you consider yourself to be exposed to the coronavirus?
How much do you think your family members are at risk for coronavirus?
B) Health and social-demographic char-acteristics
Age, educational level, gender, job monthly income level, family size, the number of family members over 60-year-old as well as under 10-year-old, the existence of members with chronic disease, expected life expectancy, insurance coverage, province of residence, exposure to Covid-19 by themselves or family members were included as health and social-demographic variables.
C) WTP for COVID-19 vaccines
Four scenarios were defined adapted from previous studies (
1,
2,
13,
21,
23, and
25-
27). The respondents explained efficacy, time of vaccination, and possible side effects in these scenarios. The participants were asked about their maximum willingness to pay in each scenario.
Figure 1 shows the hypothetical scenarios.
The respondents indicate their WTP on a payment card scale ranging from 500,000 IRR (= US$2.71) to more than 200,000,000 IRR (=US$ 870) per vaccine. Moreover, respondent could state their WTP if it was not on the scales. A pilot study with 60 individuals was conducted to determine these values through a WTP open-ended question.
Due to high fluctuation in the exchange rate, to convert values to US dollar, we used a simple moving average during the previous 200 days. Accordingly, US $1 is equal to 230,000 IRR.
Data analysis
Descriptive statistics were presented as frequency, percentage, and mean for the socio-economic demographic variables. WTP for all of the scenarios was presented as mean ± standard deviation, median, non-zero minimum, and maximum.
To predict the Covid-19 vaccine demand function in each scenario, the respondents’ WTP for the hypothetical vaccine and the number of vaccines that would be purchased at that price were used as Price and Quantity, respectively.
To model a Covid-19 vaccine demand, a semi-log regression model was used. Key variables were socio-economic demographics and Coronavirus risk assessment.
Excel 2016 and R software were used for data management and analysis, respectively.