Combined Impact of Omicron Vaccination and Environmental Risk Exposure: A Thailand Case Study

This research aimed to determine the levels of COVID-19 booster dose vaccinations in Thai populations in areas with environmental risk exposure during the Omicron outbreak. Five of twenty provinces in Thailand were selected by assessing environmental risk exposure for study settings. A total of 1038 people were interviewed by a structured questionnaire. The predicting factors of COVID-19 booster dose vaccinations were analyzed by univariate and multivariate analysis. The results showed that 69.4% (95% CI 66.5–72.1) of the population was vaccinated with COVID-19 booster doses. Multiple logistics regression revealed that the female gender (AOR 1.49, 95% CI 1.11–2.00), all age groups from 38 to 60 years old, all education levels of at least secondary school, high income (AOR 1.16, 95% CI 1.15–2.24), populations having experience with COVID-19 infection (AOR 2.27, 95% CI 2.05–3.76), knowledge of vaccine (AOR 1.78, 95% CI 1.11–2.83), and trusting attitude (AOR 1.76, 95% CI 1.32–2.36) were factors among those more likely to take COVID-19 booster dose vaccinations in high-environmental-risk-exposure areas. Therefore, an effective booster dose campaign with education programs to increase attitudes toward booster vaccinations should be implemented for the resilience of COVID-19 prevention and control.


Introduction
Various countries around the world have been concerned about the largest public health crisis since the first confirmed case of a novel coronavirus disease 2019  in December 2019 [1]. Over 300 million people with COVID-19 infections and 5.5 million deaths have been reported due to the ongoing global pandemic [2]. Effective approaches including quarantine, social distancing, and home isolation have been implemented to reduce viral transmission. However, public health and safety issues must be questioned with these approaches [3]. Hence, the COVID-19 vaccine approach with development, implementation, and uptake has been proposed for the prevention of the pandemic. Worldwide vaccine uptake is a successful and effective mechanism for COVID-19 outbreak control [4].
Shekhar et al. [5] found that vaccination against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) was the principal preventive measure against the spread of the virus and the development of severe COVID-19 diseases. An important tool for infection control, hospitalization reduction, and death from the COVID-19 pandemic has been focused on vaccines. However, global concern about the side effects of COVID-19 vaccines has arisen because of insufficient knowledge of the short-and long-term effects, distrust of vaccine companies, and the belief that the virus is not harmless [6]. Messenger RNA (mRNA) technology has been developed as the novel vaccine platform for decreasing the severity and transmissibility of SARS-CoV-2 [7]. Specifically, high efficacy values of 4.1% and 95% and 100% and 89% for COVID-19 protection against severe symptoms were significantly influenced by the Omicron variant. The population density, frequent activities, and the people's transportation in urban areas were important issues for finding sustainable epidemic and environmental risk control. Some significant environmental factors, including humidity, atmospheric temperature, and ventilation filter systems in hotels, hospitals, or houses in close contact with the population influenced the Omicron variant [30]. In addition, Sohail et al. [9] found that the virus distribution was limited by certain conditions, specifically 6 g/kg of humidity and an average air temperature above 51 F. Coccia [31] identified that the environmental exposure risk assessment of the city or pandemic areas for preventing COVID-19 exposure was limited. The reduction in COVID-19 infection rates in high-risk-level areas with environmental exposure was highlighted and challenged.
During data collection in this study, there was an Omicron variant wave of the COVID-19 outbreak in Thailand, and over 25 thousand COVID-19 cases were admitted to the hospital, with more than eighty deaths/day reported during the highest epidemic peak in Thailand from 27 March to 2 April 2022 [32]. Vaccine efficacy on the reduction in virus spreading and safe resumption of public and social activities were the main reasons for recommendation of booster vaccination uptake. Moreover, the high immunogenicity against the Omicron variant of the booster dose reduced the risk of infection [33]. Data from the Ministry of Public Health, Thailand on 2 April 2022 reported that only 34.4% of Thai people had received the third dose of vaccination [32]. Specifically, the potential risk of infectious diseases with the actual risk given by infected individuals and deaths of COVID-19 was found to be at a high level in environmental risk exposure areas, as implied by the significant spreading factors of the Omicron variant [30,31].
Therefore, the objective of this study was to determine the predictive factors of COVID-19 for booster dose vaccinations among the population in environmental risk exposure areas of Thailand during the Omicron variant outbreak. The environmental risks of exposure in areas of Thailand were investigated and adapted using the measurement by Mario Coccia [31]. These findings can propose the appropriate promotion strategy for booster dose vaccination that supports policymakers to understand the behavior pattern of COVID-19 protection in the areas of environmental risk exposure for reducing the impact of public health and economic issues caused by the pandemic.

Study Setting
The study setting in this research was selected from five provinces with the highest areas of environmental risk exposure level in Thailand. Coccia [31] identified that the factors used in the assessment of the environmental risk of exposure consisted of air pollution, wind speed, population density, and respiratory disorders of people. Hence, the sources of information and factors used for assessing the environmental risk of exposure areas in this study are presented in Table 1. The procedure for assessment of environmental risk of exposure level is as follows.
Step (1) selects the 20 Thai provinces with the highest cases of COVID-19 infection in Thailand on 7 March 2022, based on data by the Ministry of Public Health (MOPH) [32].
Step (2) cllects the data of environmental factors (Table 1) including air pollution, wind speed, population density, and respiratory disorders for the 20 provinces from Step (1).
Step (3) calculates the 25th, 50th, and 75th percentiles for data values from Step (2) of four environmental factors in the 20 provinces and categorizes the percentile values in four sets: Set 1 (lower than the 25th percentile), Set 2 (between the 25th and 50th percentiles), Set 3 (between the 50th and 75th percentiles), and Set 4 (greater than the 75th percentile).
Step (4) assigns the scores from Step (3) in the 20 provinces with a point value between 0 and 3, where Set 1 = 0, Set 2 = 1, Set 3 = 2, and Set 4 = 3. Then, the data collected from Steps (1), (2), (3), and (4) were calculated as the environmental risk of exposure level (EREL) to COVID-19 infection with using Equation (1) below: where EREL = environmental risk of exposure level, F1, F2, F3, F4 = factors used to calculate the environmental risk of exposure level to COVID-19 in a given province (F1 = air pollution, F2 = wind speed, F3 = population density, and F4 = respiratory disorders), and P k = score of a province assigned to each factor F i , with values between 0 and 3. Health Information System Development Office [37] The value of the environmental risk of exposure level ranged from 1 to 0. A value close to 1 implies a high environmental risk of exposure area to COVID-19, and a rank close to 0 indicates a low environmental risk of exposure area to COVID-19.

Population and Data Collection Procedure
The survey by face-to-face interviews was conducted on the populations in five provinces with the highest levels of environmental risk exposure from the past. The sample size of participants was calculated using a confidence interval of 95% and an acceptable error of 20. Permission for data collection was approved by the health officers in each area. According to this method, 1038 people were recruited as subjects in this study. The participants were included with the following eligibility criteria: aged over 18 years, Thai citizens, and living in the study setting for more than 6 months. The proportional random sampling by gender and age group was conducted to be representative of citizens of Thailand. Participants voluntarily agreed to enroll in this survey and take part in the research; they provided written informed consent after receipt of the recruitment procedure and research participation instructions provided by a trained research assistant. Anonymity and confidentiality of data were strictly maintained. During data collection, a research assistant followed the government policy for COVID-19 prevention and control. This research was approved by the Committee for Research Ethics (Social Science), Faculty of Social Sciences and Humanities, Mahidol University with certificate approval number 2022/033.2802 and MU-SSIRB number 2022/35(B2).

Questionnaire
The questionnaire as the measurement tool in this study was a modified version of a previous survey [38][39][40]. The pre-test process of the questionnaire was undertaken by 30 populations in another province for testing the validity and reliability of the measurement tool, with a 0.75 Cronbach's alpha coefficient. After the piloting process, the three parts relating to the objective goal of this study were the following: (1) socio-demographic status (age, gender, level of education, marital status, job, income, and COVID-19 infection history); (2) COVID-19 knowledge of infection in general, preventive behavior, and vaccination domains with 1 point for correct answers and 0 points for incorrect answers; (3) COVID-19 attitude towards risk perception and trust domains using Likert scales scored as Strongly Agree = 4, Agree = 3, Not Sure = 2, Disagree = 1, and Strongly Disagree = 0; (4) COVID-19-preventive behavior along with questions by Likert scales scored as Always = 4, Mostly = 3, Sometimes = 2, Rarely = 1, and Never = 0. A number of those receiving booster dose vaccinations were interviewed with two questions and correctly rechecked by the online vaccine certificate in the Thai formal application on a mobile phone.

Statistical Analysis
Descriptive statistics including percentages, means or medians, standard deviations, or quartile deviations were used for data analysis in this study. A univariate analysis, the Chi-square test, was used to identify the variables associated with COVID-19 booster dose vaccinations. A strong predictor for COVID-19 booster dose vaccination with p < 0.05 was identified for multivariate logistics regression. An odds ratio of association was performed by the confidence intervals of logistic regression. SPSS software version 21 was used to calculate all the statistical analyses, and the analysis was conducted at a 5% significance level. Table 2 shows the assessment level of environmental risk exposure in the 20 areas with the highest cases of COVID-19 infection in Thailand on 7 March 2022. The study areas, including twenty provinces with the highest cases of COVID-19 infections in Thailand, are shown in Figure 1. The levels of environmental risk exposure in provinces are presented as ranks between 0 and 1, and the rankings of the provinces are also from the highest risk of exposure (1.00) and lowest risk of exposure (0.17). Coccia [31] mentioned that a value of environmental risk exposure higher than 0.75 identified a high risk of exposure to COVID-19. Based on the results, five provinces in the central part of Thailand including Bangkok, Samut Prakan, Samut Sakhon, Nonthaburi, and Pathum Thani were selected as the sample areas for determining COVID-19 booster dose vaccinations among the population during the Omicron variant outbreak.   Table 3 presents the population characteristics in this study; 1038 people participated in the areas with the highest environmental risk of exposure during the Omicron variant outbreak. The percentages of the population in each province were similar in terms of ratio. Among the populations, 59.7% were female and 40.3% were male. Most (26.2%) were in the 25 to 37 age group, and a few (8.6%) were 18 to 24 years old. More than 29% of the population had completed secondary school. The majority of the population (55.5%) were married. For occupation, 35.9% of the population were general employees. The majority of the population (57.0%) had a monthly income of more than USD 367. About 43.2% of the population had previously had COVID-19, and family members were the sources of transmission.  Table 3 presents the population characteristics in this study; 1038 people participated in the areas with the highest environmental risk of exposure during the Omicron variant outbreak. The percentages of the population in each province were similar in terms of ratio. Among the populations, 59.7% were female and 40.3% were male. Most (26.2%) were in the 25 to 37 age group, and a few (8.6%) were 18 to 24 years old. More than 29% of the population had completed secondary school. The majority of the population (55.5%) were married. For occupation, 35.9% of the population were general employees. The majority of the population (57.0%) had a monthly income of more than USD 367. About 43.2% of the population had previously had COVID-19, and family members were the sources of transmission.

COVID-19 Booster Dose Vaccination
A summary of COVID-19 booster dose vaccinations among populations in the Thai areas with the highest environmental risk exposure is presented in Table 4. The results from the survey found that most populations that participated in this survey had received the COVID-19 vaccination. The number of vaccinations were first dose (2.5%), second dose (28.1%), third dose (52.9%), and fourth dose (16.5%). From this finding, the majority of the population (69.4%) reported that they were vaccinated against COVID-19 with a booster dose.  Table 5 shows the level of COVID-19 knowledge, attitude, and preventive behavior in populations in Thai areas with the highest environmental risk exposure. According to the COVID-19 knowledge, three domains of knowledge including general, preventive measurement, and vaccination were measured by a true-false test. The results showed that 62.7% and 90.8% of the population presented a high level of knowledge in general and vaccination domains, respectively. In contrast, 77.4% of the population was found to have low knowledge of the preventive measurement domain. In terms of COVID-19 attitudes, the domains of risk perception and trust were categorized by Likert scale items. Most populations had a good level of COVID-19 attitude, with 57.1% risk perception and 61.8% trust. Additionally, COVID-19 preventive behaviors of the population with Likert scale items resulted in remarkably good (77.6%) and low levels (22.4%) for preventive behaviors.

Logistic Regression Model for COVID-19 Booster Dose Vaccination
The prediction factors for COVID-19 booster dose vaccinations in the areas with the highest environmental risk exposure during the Omicron variant outbreak were identified using multiple and logistic regression analyses within the interest variables from the bivariate analysis with a p-value of 0.05. The results are shown in Table 6. For the bivariate analysis, a significant association was found between COVID- 19

Discussion
The Omicron variant of the COVID-19 epidemic outbreak also caused rapid transmission with populations in many countries including the United States [41], the United Kingdom [42], and South Africa [43]. In the context of Thailand, Suphanchaimat et al. [23] investigated the peak and daily death number of COVID-19 Omicron variant incidents. The low rate of COVID-19 vaccination was 49,523 cases by day 73 and over 270 by day 50, respectively. This study also confirmed the coverage of vaccinations to attack the Omicron variant. One-third of the peak incident cases in the worst-case scenario were reduced by a speedy vaccination rate. Hence, a program of booster dose vaccinations in Thailand should be implemented to prevent severe disease and death in the Thai people during an Omicron outbreak. Specifically, the area of high environmental risk exposure presented a significant influence via the Omicron variant [30]. In the current study, the COVID-19 booster dose vaccination of Thai people in the area of environmental risk exposure during the Omicron outbreak was determined.
The levels of environmental risk exposure in highly endemic provinces of Thailand were assessed by environmental factors adapted from Coccia [31], including air pollution, wind speed, population density, and respiratory disorders. The results identified that five provinces in Bangkok metropolitan areas had the highest levels of environmental risk exposure to a viral agent because of the high concentration of air pollution in the pattern of PM 10, which can be supported by the longer period and diffusion ability of COVID-19 outdoors as well as expanded human transmission in public areas [27,28]. The province with the highest level of environmental risk exposure in this study was Samut Sakhon, which was caused by the high total days exceeding the limits set for PM 10, low wind speed, high density of population, and high rates of mortality for lung cancer (data not shown). Consistent with the report from Yamsrual et al., [44] found that Samut Sakhon populations indicated that the main environmental problems in their perception were air and water pollution and odors. From these findings, the prevention and control of environmental pollution in Thai provinces can reduce the potential risk of COVID-19 transmission. The proposed concept of environmental risk exposure can promote an up-to-date policy that supports policymakers to understand the knowledge gap in infectious disease transmission and protect from a new wave of COVID-19 as well as new viral agents in the potential risk areas of Thailand.
The current survey found that nearly 70% of populations in the areas with environmental risk exposure took COVID-19 booster dose vaccinations. This uptake rate of COVID-19 vaccination was higher compared with the findings from a current systematic review and meta-analysis in the world setting on COVID-19 booster dose vaccination by Abdelmoneim et al. [45]. The uptake rate of the COVID-19 booster dose vaccination from eight publications around the world with 12,995 participants was 31%. In addition, only 28.8% of the population in Bangkok received the booster dose from September to December 2021. During the data collection period (March 2022-June 2022), it was found that the uptake rate of COVID-19 booster doses in the Bangkok Metropolitan Region in this study was 2 times higher than the previous report 3 months later [46] because the risk of transmission and safe activity resumption in the public area were elicited by taking COVID-19 booster vaccinations during the rise of the Omicron variant [33]. The policy of COVID-19 booster doses among the entire population was strongly supported by the Thai government [25]. Hence, the areas with high environmental risk exposure and high incidences of COVID-19 infection were the priority targets for vaccination coverage in Thailand.
The results from multiple logistics regression analysis found that the groups of population characteristic factors including female gender, all age groups from 38-60 years, all education levels of at least secondary school, and high income were predictors of COVID-19 booster dose vaccination uptake among the populations with the highest levels of environmental risk exposure in Thailand. Some research [47,48] identified that there were no significant differences found between males and females in terms of COVID-19 vaccine acceptance. In the present study, females had more COVID-19 vaccinations than males. This finding was consistent with the report among the global population [49], global dental students [50], and Palestinian dental students [51]. Urrunaga-Pastor Diego et al. [52] reported that the anti-vaccine groups in the female gender had lower exposure than the male. In addition, Thai females were more likely to engage in preventive health behaviors against COVID-19 infection than males [53]. Hence, the uptake of COVID-19 booster dose vaccination was employed by Thai women during the time of this research survey. In terms of age group, being aged between 25 and 54 years old was a strong predictive factor for COVID-19 vaccination booster dose because these people were more willing to accept and follow the recommendations of the vaccine policy [41]. Consistent with our findings in this study, the age groups of 38-45 years, 46-53 years, and over 54 years in the studied populations were found to predict COVID-19 booster dose vaccination. However, the results of knowledge in the present study found that populations with a higher level of education (at least secondary school) exhibited more COVID-19 booster dose vaccinations because broad information about the side effects of vaccinations would be screened and analyzed by educated population groups [54]. Regarding the role of economic status as a determinant of COVID-19 booster vaccination, the high-income population groups were more likely to accept the booster doses because having lower-income status may cause hesitation to take booster doses because of losing income due to illness from the side effects of vaccines [55]. Not surprisingly, those having experience with COVID-19 infections were significantly less likely to take COVID-19 booster dose vaccinations. Various studies [56,57] implied that population groups having experience with COVID-19 infections were more likely to accept the COVID-19 vaccination. Al-Hatamleh Mohammad A. I. et al. [58] reported that many symptoms, including general fatigue, headache, fever, anosmia, and cough, were the most frequent health burdens of COVID-19 infection. Populations were willing to take the COVID-19 booster dose vaccinations for reducing the suffering of COVID-19 infections [59].
The current study found that a strong predictor of COVID-19 booster vaccination among populations in the areas with environmental risk exposure was knowledge level concerning vaccination. Consistent with the previous research in Thailand [53] and Italy [60], it was identified that the high knowledge of respondents on vaccines was significantly associated with vaccination acceptance and uptake against COVID-19, because individual experience towards the learning process would change health and self-care behaviors [61]. Comprehensive knowledge of COVID-19 infections may induce people to accept vaccinations to protect themselves and their family members [62]. Finally, COVID-19 attitude on trust predicted an enhancement of COVID-19 booster dose vaccinations [63], implying that trust in COVID-19 vaccinations is associated with the acceptance rate of COVID-19 booster dose vaccinations. For the populations with good attitudes, the level of awareness could be increased by having an appropriate attitude during a pandemic [64].
This study highlighted the need to develop a specific recommendation for the enhancement of booster vaccinations in high-risk areas for infection transmission in the context of environmental exposure. The significant benefits on environmental, public health, social, and economic issues in cities can be enhanced by pollution reduction, and the risk of transmission in cities can be reduced for any new wave or future pandemics of COVID-19 [28]. In addition, this study contributes to the understanding of how to increase motivation in the unvaccinated groups in high-risk areas. Knowledge of booster doses and trusting attitudes were the main factors for increasing the uptake rate of COVID-19 booster doses in these areas. Hence, an effective booster dose campaign with an education program on effectiveness and safety to increase attitude levels on booster vaccination should be implemented to increase the COVID-19 booster dose vaccinations throughout the country and increase the resilience performance of COVID-19 prevention and control [65].

Conclusions
The recommendation for booster dose vaccination uptake was a global approach to COVID-19 outbreak prevention during the Omicron variant. The rapid spread of COVID-19 infections in a city was stimulated by social interaction as well as the environmental risk exposure factor. Thus, the widespread distribution of COVID-19 booster dose vaccination was provided by the Thai government during that crisis. The findings from this survey determined the crucial knowledge on prediction factors for the booster dose of the COVID-19 vaccination in the high-risk areas of Thailand in the environmental exposure context. To sum up, good knowledge of booster dose vaccination and a good attitude with trust were found to be strong predictors of COVID-19 booster dose vaccination among populations in the areas with a high risk of environmental exposure. Therefore, an educational campaign on the effectiveness and safety of vaccinations was still demanded to expand public attitudes toward COVID-19 booster dose vaccinations [46] and was urgently needed in Thailand [47]. From this result, the findings imply that the potential risk of transmission with the pollution reduction in cities can be deduced for the incident rate of future COVID-19 pandemics. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. Written informed consent has been obtained from the subjects to publish this paper. Data Availability Statement: Not applicable.