Characteristics of Asymptomatic COVID-19 In SARS-COV-2 Vaccine Trial Screening Participants

1. INTRODUCTION

COVID-19 has spread rapidly worldwide [1]. To prevent the spread of infection, the Indonesian government has implemented several policies, including physical distancing, large-scale social restrictions, and a social safety net [2]. According to the WHO, until November 2022, there have been millions of confirmed cases and hundreds of thousands of deaths worldwide, including in Indonesia [3]. The Indonesian government continues to take steps to prevent the spread of the virus by developing a domestic COVID-19 vaccine. Since November 2021, PT Bio Farma (a pharmaceutical company under the Ministry of State-owned Enterprises in Indonesia) has started the manufacturing process of a recombinant protein subunit vaccine for COVID-19 through clinical trials over the country [4].

Patients with COVID-19 commonly have a series of symptoms such as fever, cough, fatigue or myalgia, diarrhea, shortness of breath, anorexia, and headache [5–7]. But asymptomatic cases have also been found [8]. According to WHO interim laboratory testing guidelines for a suspected patient with COVID-19, an asymptomatic patient showed a positive real-time polymerase chain reaction (RT-PCR) and a high-intensity contact history with a COVID-19 case [9]. Studies showed that asymptomatic cases had a similar viral load to the symptomatic patient, so close contacts are equally susceptible to transmission of both asymptomatic and symptomatic instances [10]. Asymptomatic or mild COVID-19 infections are frequently experienced by young persons individuals and adults in middle age with individual functional statuses and no underlying disease [11, 12]. However, given the length of sickness in the asymptomatic group was strongly connected with patient age, symptoms are more likely to appear during the course of the disease in older asymptomatic individuals [13].

The increasing evidence of asymptomatic infections of COVID-19 needs to be a concern because the person with asymptomatic infections mainly do not seek medical assistance even though they can still transmit the virus to others [11]. Early identification of the infected person is essential to cut off the route of COVID-19 transmission and assist medical professionals in facilitating appropriate corrective actions and reducing COVID-19 mortality [12, 14]. The purpose of this study is to know the traits of the COVID-19 asymptomatic patient in vaccine clinical trial subjects to help identify and develop the mitigation strategy to decrease the transmission of this clinical feature.

2. METHODS

3. RESULTS

In this study, 219 participants were enrolled. The majority of participants were male (63.5%). Most participants with positive PCR SARS-CoV-2 results were less than 60 years old (89.6%), with a mean age of 40 years, ranging from 18-70 years old. All participants reported no symptoms associated with COVID-19 according to the screening record form and physical examination. Based on the result of the RT-PCR test, 106 (48.4%) participants were categorized as having positive PCR SARS-CoV-2 results, and 113 (51.6%) had negative results. The average cycle threshold (Ct) values in COVID-19-positive cases were 28.29 ± 6.74 (min 12.70, max 37.87) for the helicase gene and 29.71 ± 6.29 (min 15.00, max 38.00) for RNA-dependent RNA polymerase (RdRp) gene. Participants who lived in Mranggen Demak had a higher positive PCR SARS-CoV-2 percentage (58.5%) than patients residing in Jepara (41.5%). It might be because Mranggen was an industrial area and the majority of participants occupation in this study were formal workers (61.9%), such as factory workers, private employees, traders, and teachers, who have a greater risk of person-to-person transmission than non-formal workers (3.5%). Most educated participants with positive PCR SARS-CoV-2 results were in elementary school (30.2%), while the majority of participants with negative PCR SARS-CoV-2 results finished their education in junior high school (31.9%). The participants’ characteristics are presented in Tables 1 and 2. PCR SARS-CoV-2 positive participants with high blood pressure (28.3%) were lower than those with negative results (66.4%). Meanwhile, from the BMI results, most participants with positive PCR SARS-CoV-2 results had a BMI over 22.9 kg/m2 or included overweight BMI (51.9%). Blood glucose examination showed that most participants with positive PCR SARS-CoV-2 results had normal blood glucose (89.6%), but the high total cholesterol was higher (59.4%) among participants with positive results. According to the chi-square test, there was no significant difference between PCR SARS-CoV-2 results with the demographics characteristics and physical examination results (p-value >0.05).

As for laboratory findings in participants with positive PCR SARS-CoV-2, the result showed leukocytosis in 13 participants (12.3%) with a mean of 8.3 mg/dL, thrombocytosis in 15 participants (14.2%) and 48 participants (45.3%) had hemoglobin level out of normal range. Inflammatory markers showed participants with positive PCR SARS-CoV-2 results; there were only 7 participants (6.6%) with high NLR and 2 patients (1.9%) with high ALC. In addition, IL-6 results in participants with positive PCR showed increased levels in 15 patients (14.2%), while the other 91 participants (85.8%) had normal IL-6 levels. There was no strong evidence for the association between PCR SARS-CoV-2 results and hemoglobin level (p-value=0.810), leukocyte count (p-value=0.077), thrombocyte count (p-value=0.427), NLR (p-value=0.889), ALC (p-value=0.142), AST (p-value=0.771), ALT (p-value=0.680), ureum (p-value=0.301), creatinine (p-value=0.084), and IL-6 (p-value=0.218). The bivariate analysis is presented in Table 3.

4. DISCUSSION

This study found that the percentages among the positive and negative PCR SARS-CoV-2 results in the asymptomatic participants were not too different. Based on the results of the RT-PCR SARS-CoV-2 examination, it was found that the mean Ct-values in participants with positive PCR results were included in a medium level of viral load based on the study of Magleby et al. [16]. In a previous study, Gulbudak et al. studied Ct-value patients and found that the RdRp gene Ct-value in asymptomatic patients was significantly higher than in symptomatic patients [17]. However, the participants in this study were healthy asymptomatic patients, so there was no data regarding Ct-values in participants with symptoms related to COVID-19. Another study found a similar viral load detected both in an asymptomatic and symptomatic patient, which suggests the transmission potential of an asymptomatic or mild symptomatic patient [18]. The result of this study should be a concern due to the high percentage of asymptomatic participants, but it has potential transmission and risk for other asymptomatic communities [13, 19]. Prior studies demonstrated that in COVID-19 patients, Ct values could not be used as the only indicator of disease severity. Clinicians should evaluate additional clinical parameters in addition to Ct values, such as age, co-morbidities, and laboratory data [20].

Based on the region of residence in this study, there were slightly more positive PCR SARS-CoV-2 results in participants residing in the Mranggen district, Demak, than in the Pecangaan district, Jepara regency. This could be because both Demak and Jepara are industrial areas, so the population's mobility is quite high, and many residents work in the public sector. We also suggest that one of the reasons for the high percentage of asymptomatic participants with positive PCR results in this study was related to the spread of the omicron variant in Indonesia since December 2021 [21]. Omicron has a substantially greater rate of asymptomatic carriage than another variant of concern, according to a prior study, and is probably a significant contributor to the variant's rapid and widespread global spread [22]. Additionally, investigations have shown that SARS-CoV-2 infections that are asymptomatic or barely symptomatic are likely ignorant of their infectious status, which can lead to outbreaks and continuous rapid person-to-person transmission [19].

The result revealed that the majority of the subjects worked in occupations such as factory workers, private employees, traders, and teachers, where these jobs have relatively high mobility. Previous studies showed that occupation does not impact the virus's ability to spread in the community [23]. However, there was a more significant risk of COVID-19 infection among critical professionals, particularly those in social and educational fields [24]. Furthermore, Yanik et al. studied occupational characteristics correlated with COVID-19 infection among people in the United Kingdom and discovered that the probability of COVID-19 infection was higher in jobs that did not allow for remote work [25].

The laboratory findings in this study showed no significant differences between the positive and negative PCR results. This follows other studies that found no significant difference in laboratory results with the symptoms experienced in patients with COVID-19 infection [10, 13]. The previous study showed a patient with infected COVID-19 usually has a normal leukocyte count [26–28], leukocytosis, and lymphopenia [7, 26, 27] but among the study's asymptomatic subjects, these changes were uncommon. It has been known that elevated NLR and decreased ALC in a patient with COVID-19 are correlated with severity and reliable indicators of death as an outcome of COVID-19 disease [29, 30]. Increased IL-6, a marker of inflammation, has been linked to a higher risk of mortality in individuals with severe symptoms [31]. However, in this study, these indicators could not be used as a comparison because the participants tested were healthy, asymptomatic participants. There was no further follow-up regarding the participant's condition.

5. LIMITATIONS

This study has several limitations. First, laboratory parameters used were based on FDA toxicity guidelines for clinical trials, so some laboratory parameters could not be evaluated in this study. Second, there is a possibility of information or recall bias where the subject does not provide truthful data about the condition and symptoms experienced correlated with COVID-19 because they want to participate in clinical trials. Third, follow-up was not carried out on the subject, so whether any symptoms and kinetic profile of laboratory parameters developed afterward was not known. The Indonesian government should consider current findings when formulating COVID-19 patient testing, tracing, and treatment policies. Even though subjects are asymptomatic, the transmission of viruses still occurs with the same risk as symptomatic patients. Therefore, further extensive screening is needed with the participation of the government to reduce morbidity and mortality due to COVID-19, especially in Indonesia.

CONCLUSION

In this vaccine trial screening phase study, we found that almost half of the participants were ineligible due to having asymptomatic SARS-CoV-2 infection. Meanwhile, from the characteristics and laboratory findings, we found no significant relationship with the PCR results in the participants of this study. Even so, it is necessary that people with asymptomatic COVID-19 infection still need to be concerned because they have the same transmission potential as symptomatic ones.

REFERENCES