Investigating the Pre- and Post-COVID-19 Vaccination Infection Status of Iranian Dental Students: A Cross-Sectional Study

doi:10.21203/rs.3.rs-5209954/v1

Background: Dental students have the potential risk of COVID-19 exposure due to close contact with patients and aerosol-generating procedures. This study aims to touch upon the frequency of COVID-19 infection after different doses of vaccination among Iranian dental students in 2022.

Methods: A cross-sectional study was used to collect self-reported COVID-19 status. A total of 261 dental students volunteered to participate in the study. A total of 252 valid forms were gathered, with a response rate of 96.55%. Data analysis was performed using descriptive statistics, mean and standard deviation, and Chi-square and Fisher exact tests by Spss17 (Chicago, USA) software.

Results: The rate of COVID-19 infection significantly decreased after the first and third doses of vaccination. The rate of COVID-19 infection was not very different after the first, second, and third doses of the vaccine according to the type of vaccine. Despite gender, there was no significant difference between the study year and type of vaccine with the frequency of COVID-19 involvement. Serious complications following injection of AstraZeneca vaccine in all doses were observed in comparison to other types.

Conclusion:

Vaccination could decrease the rate of COVID-19 infection among dental students. The duration of COVID-19 infection also decreased after administration of different vaccine doses. There was no significant difference in the infection rate among students based on the type of vaccine received. Further studies should be conducted to explore the potential side effects and long-term effectiveness of the COVID-19 vaccines.

COVID-19

vaccination

prevalence

dentistry

students

The COVID-19 epidemic has changed the daily plans of people and has led to concerns regarding their health and welfare (1). In symptomatic patients, clinical demonstrations of this disease usually begin after less than a week including fever, cough, nasal congestion, fatigue, and other symptoms of upper respiratory tract infection (2). In specific cases, especially in the elderly, coronavirus infections may lead to pneumonia and subsequently the death of the sufferer (3). The continual COVID-19 pandemic has not only resulted in devastating consequences in terms of cases of infection and mortality but has also affected various approaches to the education of medical sciences and treatment, including dentistry. Therefore, they are considered a high-risk group for infection or disease transmission. Thus, early vaccination of dental teams, including dental students, is very important (4). Adequate uptake of an effective vaccine may induce collective immunity (5). Fear of complications and uncertainty about the effectiveness of the vaccine drives people to hesitate to use the COVID-19 vaccine (6). Due to reasons such as the lack of 100% effectiveness of vaccines, lack of complete vaccination, and individuals’ behavior and culture of prevention, people must continue to observe appropriate health behaviors (7). Besides, vaccinated people ought to take necessary precautions into account. Preliminary data suggest that vaccines may be less effective against some species; so, receiving a vaccine does not mean the end of public health and preventive measures (8). Due to the existing conditions surrounding the continued epidemy despite the high coverage of vaccination, the unknown effectiveness of vaccination against different strains, and the unavailability of accurate statistics of dental students' infection, this study aimed to touch upon the frequency of COVID-19 infection after various doses of vaccination among dental students.

Operational definitions are explained as follows:

Fully vaccinated: Subjects who received two doses of a two-dose vaccine series and ≥ 14 days had elapsed since the second dose (9).

Partially vaccinated: Persons who received one dose of a two-dose series (9).

This descriptive cross-sectional study was conducted at Yazd Dental School from 24 September 2022 to 21 December 2022, from the 3rd to the 6th academic year. A total of 261 students were included. Non-probability consecutive sampling was used for the selection of patients.

Inclusion criteria: All final-year dental students who had received at least one dose of the COVID-19 vaccine were included.

Exclusion criteria: Subjects on immunosuppressive drugs and autoimmune diseases were excluded.

Data Collection: In the current study, data were collected by interviews with an in-paper Questionnaire. All participants meeting inclusion criteria were included after informed consent. Demographic data regarding age, gender, and academic year were collected. Information regarding vaccination status, vaccine brand, infection status before and after vaccination, disease severity, serious complications experienced after immunization, and the time between the last dose of vaccine and COVID-19 infection were noted. SARS-CoV-2 vaccination status was classified into three categories as defined in the operational definitions fully vaccinated, and partially vaccinated based on the vaccination status (9). The disease status of patients was classified into ICU admission, hospital admission, outpatient treatment, and home care.

To distribute these Questionnaires, final-year dental students were enlisted as intermediaries, and they distributed them to students in their 3rd to 6th academic years at the Yazd Dental School. Before distributing the Questionnaires, the students were provided with comprehensive explanations regarding the study's design and objectives.

Sampling Technique: Non-probability consecutive sampling.

Data Analysis

After collecting the required data, they were imported into SPSS 17. The required tables and indices were prepared. Chi-square and Fisher exact tests were used for statistical calculations (P<0.05).

Ethical Considerations

To comply with ethics in research, first, the purpose of the study was explained to the study subjects. Then, their informed written consent for participation in the study was obtained. They were also assured of their information confidentiality and anonymity. The study conformed to the Declaration of Helsinki guidelines and was approved by the ethics committee of Yazd Shahid Sadoughi University of Medical Science, Yazd, Iran with the ethics code: IR.SSU.DENTISTRY.REC.1401.044. All methods were performed per the relevant guidelines and regulations.

In this study, a total of 261 Questionnaires were distributed, and 252 of these were fully completed by dental students. Among the participants, 132 (52.4%) were male, and 120 (47.6%) were female. The mean age of the study's participants was 23.98 years, with an age range spanning from 20 to 35 years. Moreover, 157 students (62.3%) resided in private homes, while 95 students (37.7%) lived in dormitories. The descriptive characteristics of participants are shown in Table 1. The frequency of COVID-19 infection, as related to evaluated variables, is detailed in Table 2.

Table 1. Descriptive characteristics of participants

variables

N (%)

Gender

Male

female

132(52.4)

120(47.6)

Age range

20-24

25-35

162(64.29)

90(35.71)

Academic year

3

4

5

6

63(25)

Residency status

Dormitory

Private home

85(37.7)

157(62.3)

Vaccine dose

1

2

3≤

4(1.6)

69(27.4)

179(71)

Table 2. The distribution of COVID-19 infections is based on different variables based on vaccination status

After the third dose

N (%)

Fully vaccinated

N (%)

Partially Vaccinated

N (%)

Before vaccination

N (%)

Variables

46(50)

41(46.6)

68(52.7)

58(48.7)

55(41.7)

41(34.2)

79(59.8)

61(50.8)

Gender

Male

Female

0.260

0.532

0.221

0.15

P-value*

73(47.7)

14(51.9)

102(49.5)

24(57.1)

82(39.2)

14(32.6)

115(55)

25(58.1)

Age range

20-24

25-35

0.157

0.812

0.674

0.140

P-value*

35(44.9)

52(51)

49(52.7)

77(49.7)

36(37.9)

60(38.2)

51(53.7)

89(56.7)

Residency status

Dormitory

Private home

0.012

0.646

0.959

0.642

P-value*

16(40.8)

22(56.4)

27(50)

22(46.8)

30(48.4)

32(52.5)

39(61.9)

25(40.3)

25(39.7)

27(42.9)

24(38.1)

20(31.7)

30(47.6)

39(61.9)

35(55.6)

36(57.1)

Academic year

3

4

5

6

0.525

0.110

0.626

0.440

P-value*

93(36.9)

27(10.7)

26(14.4)

34(18.8)

122(48.4)

39(15.5)

44(17.5)

43(17.1)

156(61.9)

43(17.1)

21(8.3)

32(12.7)

112(44.4)

65(25.8)

22(8.7)

53(21.1)

Infectious status

No infection

PCR test (+)

PCR test (-)

Symptomatic Without PCR test

49(55.7)

24(27.3)

10(11.4)

5(5.7)

57(45.2)

28(22.2)

25(19.8)

16(12.7)

46(47.9)

27(28.1)

12(12.5)

11(11.5)

52(36.9)

55(39)

21(14.9)

13(9.2)

Duration of infection

3-5 days

5-14

14-21

21<

0(0)

3(3.4)

14(15.9)

71(80.7)

0(0)

10(7.9)

26(20.6)

90(71.5)

1(1)

6(6.3)

16(16.7)

73(76)

1(0.7)

23(16.3)

32(22.7)

85(60.3)

Severity of disease

ICU admission

Hospital admission

Outpatient treatment

Home care

*Chi-square test

Regarding the number of COVID-19 vaccine doses received by the participants, the data indicated that at the time of completing the forms, over half of the students (61.9%) had received three doses of the vaccine, with only 4 students (1.6%) have received just the first dose. The infection status, duration of COVID-19 infection, and its severity are presented in Table 2.

When assessing the frequency of serious side effects following vaccination (within 48 hours after vaccination), it was observed that more than half of the students experienced serious side effects after receiving the first vaccine dose. The occurrence of serious side effects (within 48 hours) was significantly different based on vaccine type in partially and fully vaccinated students (Table 3). Details regarding the rate of COVID-19 infection, and the time between vaccination and COVID-19 infection based on vaccination status are shown in Table 4.

Table3. The occurrence of serious side effects (within 48 hours) based on vaccination status

After the third dose

N (%)

fully vaccinated

N (%)

partially vaccinated

N (%)

Variables

6(9.2)

11(13.6)

1(4.3)

0(0)

11(12)

36(29)

8(27.6)

1(33.3)

26(25.7)

108(83.4)

8(47.1)

1(25)

serious side effects

Sinopharm

AstraZeneca

sputnik

others

0.359*

0.027*

0.0001*

P-value

*Fisher exact test

Table 4. Frequency of the rate of COVID-19 infection and the time between vaccination and COVID-19 infection based on vaccination status

After the third dose

N (%)

fully vaccinated

N (%)

partially vaccinated

N (%)

variables

27(42.9)

39(50.6)

11(47.8)

6(54.5)

46(50)

59(47.7)

20(69)

1(33.1)

39(38.6)

47(36.2)

8(47.1)

2(50)

vaccine type Sinopharm

AstraZeneca

sputnik

others

0.754*

0.194**

0.777**

P-value

28(11.1)

13(5.2)

14(5.5)

33(13.1)

36(14.3)

22(8.7)

21(8.3)

47(18.7)

30(11.9)

12(4.8)

15(5.9)

39(15.5)

The time between vaccination and infection

0-2 weeks

2-4

4-8

8<

*Chi-square test

**Fisher exact test

Assessing the risk of COVID-19 infection among dental students is crucial, given their close patient contact and exposure to aerosols within the dental field (10–12). Sherman et al.'s study in 2021 revealed that the inclination towards vaccination correlated with age, with higher tendencies among older individuals (3). Additionally, this inclination was more pronounced among males and married individuals (13). This gender difference may be attributed to a higher infection rate among males, as statistics indicate a greater male mortality rate due to COVID-19, potentially due to increased exposure (14). Conversely, vaccine hesitancy appeared more common among women, possibly linked to their role in investigating and managing family health matters (15). In our study, vaccine uptake data showed that 1.6%, 27.4%, 61.9%, 8.7%, and 0.4% of participants had received the first to fifth vaccine doses, respectively. In a similar study, 6.3% of students hadn't received any vaccine dose, while 2.5%, 36.7%, 54.2%, and 0.4% had received one to four doses of the vaccine (16). A systematic review identified common vaccine complications, including pain at the injection site, fatigue, headache, fever, and muscle pain. AstraZeneca and Sputnik vaccines exhibited more complications, while the Sinopharm vaccine had the least reported complications (17). Our study revealed significantly higher serious complications after the first, and second doses of the AstraZeneca vaccine. Other studies also noted more frequent vaccine-related complications in females, those over 39 years old, and recipients of mRNA vaccines (18). One study reported serious side-effect rates of 32.6%, 33.8%, and 32.8% after the first, second, and third doses, respectively (16). In contrast, our study found rates of 56.7% after the first dose and 22.2% after the second dose. This variation may result from differences in vaccine types and genetic backgrounds between Asian and European populations (16). Our study showed no significant difference in infection rates according to vaccine type. This differs from Antonelli et al.'s study in the United States (19). However, confounding factors may affect vaccine type selection based on age and demographics.

This study, conducted two years after the outbreak, revealed a 25.8% infection rate based on a positive PCR test among dental students before vaccination, which decreased after vaccination. This is higher than infection rates reported in the early months of the outbreak (20, 21). The study highlights the need for ongoing vigilance and the possibility of different vaccine types affecting outcomes.

In the Czech Republic, the prevalence of COVID-19 among students was reported at 37.1% based on a positive test, while at the same time, it was significantly lower than its rate among ordinary people (45.1%) (12). Another study revealed that dental students presented less serious symptoms of the disease than other people in the community (11). It may be concluded dental students are somewhat immune to COVID-19 due to frequent and protected exposure to the virus.

Our findings suggest that there was no statistically significant difference between the two genders. It goes in line with Bani Hani et al (22), while it was inconsistent with similar studies (10, 11). In some studies, the higher infection rate of males before vaccination is possibly due to greater community exposure (23). However, within the student population, exposure levels were more balanced. Some kinds of literature believed the differences may be attributed to biological or hormonal factors (24–28). Additionally, long-term complications of COVID-19 infection may differ by gender (29, 30).

Our study found no significant difference among academic years before and after the vaccination, with third-year students experiencing fewer infections. Schmidt declared there was no difference based on infection rate among different academic years, too(12). This finding is the opposite of Bani Hani et al (22) .Possible explanations for differences in studies include reduced patient contact, greater fear of COVID-19, and less clinical exposure, which warrant further investigation (31, 32).

The study observed that the longest infection interval after vaccination occurred more than 8 weeks after receiving the vaccine, irrespective of the dose. This aligns with Antonelli et al.'s findings (33). Severity, indicated by outpatient or inpatient care, decreased after vaccination. Severity, indicated by outpatient or inpatient care, decreased after vaccination. Of course, a significant difference in disease severity before and after vaccination was noted in some prior studies (10, 33).

So, in Schmidt's study, the mean duration of the disease was 7 days in the patients who received two doses of the vaccine and 11 days in those who did not receive it; the difference was statistically significant (16). Another study in the United States revealed that those suffering from COVID-19 symptoms who were vaccinated had fewer symptoms during the first week of the disease and less need to be hospitalized (33). In the present study, the duration of infection based on time intervals clearly showed that the duration of infection for more than 14 days was reduced after vaccination; this value correlates favorably with another study (33). A similar study in the Czech Republic indicated that there was no statistically significant difference in initial infection rates between students who received two doses of vaccination and those who did not receive the full dose. Nevertheless, there was a statistically significant difference between the infection rate of people who did not receive two full doses and those who received a booster dose. Finally, there was no significant difference between the infection rates of people with two doses and three doses of the vaccine (12).

Although the use of the self-report questionnaire for COVID-19 symptoms may be considered a study limitation, the results of this study can still be valuable during the COVID-19 epidemic. This is because, at the time of the study, all symptoms were thought to be similar to those of a common cold. Due to this fact, symptomatic students with negative PCR tests were considered infected.

Finally, this study's census sampling method, which included all students with patient exposure, enhances its reliability compared to prior research. The relatively equal gender participation rate of 1.1:1.0 further strengthens the results. Nonetheless, limitations include single-centre data, potentially limiting generalizability. Another limitation that should not be ignored is memory bias. In studies, information collected retrospectively, with self-reported data is highly susceptible to this bias and cannot accurately reflect infection status. This survey is a pilot study on SARS-COV-2 infection in 2022, at that stage of the pandemic reinfections become more and more common. Future research should examine vaccine side-effects and effectiveness over extended periods, making decisions on continued university population vaccination against COVID-19.

A decreasing trend was observed in the COVID-19 infection rates among dental students before vaccination compared to after vaccination. The duration of COVID-19 infection decreased after receiving different vaccine doses. There was no significant difference in the infection rate among students regarding the type of vaccine in any of the vaccine doses. Further studies are recommended to investigate vaccines' side effects and efficacy over longer periods.

Authors’ contributions

F.O Developed the initial concept of study. F.O and MJ. K contributed to the study design and wrote the manuscript. MJ. K collected the data, and FO oversaw the data collection. M.K contributed to the methodology analysis and interpretation of data. M.K and F.O contributed to data analysis. All authors revised and approved the final manuscript.

Conflict of interest

The authors declare that they have no conflict of interest regarding the present manuscript.

Acknowledgement

This study has been supported financially by the Vice Chancellor for Research and Technology of Yazd Shahid Sadoughi University of Medical Sciences.

Availability of data and materials

All data analyzed during this study are included in this published article. If any additional data/files may be obtained from the corresponding author on reasonable request.

Funding

This work was supported by the Vice Chancellor for Research and Technology of Yazd Shahid Sadoughi University of Medical Sciences (13534). The funding body had no part in the design of the study, data collection, analysis, or interpretation of data, or in writing the manuscript.

Ethics approval and consent to participate

Informed, written consent was obtained from all subjects. The study conformed to the Declaration of Helsinki guidelines and was approved by the ethics committee of Yazd Shahid Sadoughi University of Medical Science, Yazd, Iran (ref no: IR.SSU.DENTISTRY.REC.1401.044). All methods were performed per the relevant guidelines and regulations.

Ghadirian H, Khami M, Tabatabaei S, Mirhashemi A, Bahrami R. COVID-19 vaccination and psychological status of Iranian dental students. Front public health. 2022;10:946408.
Velavan TP, Meyer CG. The COVID-19 epidemic. Tropical medicine & international health. TM IH. 2020;25(3):278–80.
Sherman SM, Smith LE, Sim J, Amlôt R, Cutts M, Dasch H, et al. COVID-19 vaccination intention in the UK: results from the COVID-19 vaccination acceptability study (CoVAccS), a nationally representative cross-sectional survey. Hum vaccines immunotherapeutics. 2021;17(6):1612–21.
Mascarenhas AK, Lucia VC, Kelekar A, Afonso NM. Dental students' attitudes and hesitancy toward COVID-19 vaccine. J Dent Educ. 2021;85(9):1504–10.
Thunström L, Ashworth M, Finnoff D, Newbold SC. Hesitancy Toward a COVID-19 Vaccine. EcoHealth. 2021;18(1):44–60.
Chutiyami M, Salihu D, Bello UM, Winser SJ, Gambo AA, Sabo H et al. Are Fear of COVID-19 and Vaccine Hesitancy Associated with COVID-19 Vaccine Uptake? A Population-Based Online Survey in Nigeria. Vaccines. 2022;10(8).
Skafle I, Nordahl-Hansen A, Quintana DS, Wynn R, Gabarron E. Misinformation About COVID-19 Vaccines on Social Media: Rapid Review. J Med Internet Res. 2022;24(8):e37367.
Rodrigues CMC, Plotkin SA. Impact of Vaccines; Health, Economic and Social Perspectives. Front Microbiol. 2020;11:1526.
Teran RA, Walblay KA, Shane EL, Xydis S, Gretsch S, Gagner A et al. Postvaccination SARS-CoV-2 infections among skilled nursing facility residents and staff members - Chicago, Illinois, December 2020-March 2021. American journal of transplantation: official journal of the American Society of Transplantation and the American Society of Transplant Surgeons. 2021;21(6):2290–7.
Abu-Hammad O, Alnazzawi A, Babkair H, Jambi S, Mirah M, Abdouh I, et al. COVID-19 infection in academic dental hospital personnel; a cross-sectional survey in Saudi Arabia. Int J Environ Res Public Health. 2021;18(20):10911.
Sarkarat F, Tootoonchian A, Haraji A, Rastegarmoghaddam Shaldoozi H, Mostafavi M, Naghibi Sistani SMM. Evaluation of dentistry staff involvement with COVID-19 in the first 3 month of epidemiologic spreading in Iran. J Res Dent Sci. 2020;17(2):137–45.
Schmidt J, Vavrickova L, Micopulos C, Suchanek J, Pilbauerova N, Perina V, et al. COVID-19 among Czech Dentistry Students: Higher Vaccination and Lower Prevalence Compared to General Population Counterparts. Vaccines. 2022;10(11):1927.
El-Elimat T, AbuAlSamen MM, Almomani BA, Al-Sawalha NA, Alali FQ. Acceptance and attitudes toward COVID-19 vaccines: A cross-sectional study from Jordan. PLoS ONE. 2021;16(4):e0250555.
Galbadage T, Peterson BM, Awada J, Buck AS, Ramirez DA, Wilson J, et al. Systematic Review and Meta-Analysis of Sex-Specific COVID-19 Clinical Outcomes. Front Med. 2020;7:348.
Shaw J, Stewart T, Anderson KB, Hanley S, Thomas SJ, Salmon DA, et al. Assessment of US Healthcare Personnel Attitudes Towards Coronavirus Disease 2019 (COVID-19) Vaccination in a Large University Healthcare System. Clin Infect diseases: official publication Infect Dis Soc Am. 2021;73(10):1776–83.
Schmidt J, Vavřičková L, Micopulos C, Suchánek J, Pilbauerova N, Perina V, et al. COVID-19 among Czech Dentistry Students: Higher Vaccination and Lower Prevalence Compared to General Population Counterparts. Vaccines. 2022;10:1927.
Moradi A, Azarmi S. Review of the side effects of Covid-19 vaccines: A narrative review. J Military Health Promotion. 2021;2(2):365–75.
Riad A, Põld A, Kateeb E, Attia S. Oral Adverse Events Following COVID-19 Vaccination: Analysis of VAERS Reports. Front public health. 2022;10:952781.
Antonelli M, Penfold RS, Merino J, Sudre CH, Molteni E, Berry S, et al. Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app: a prospective, community-based, nested, case-control study. Lancet Infect Dis. 2022;22(1):43–55.
Araujo MW, Estrich CG, Mikkelsen M, Morrissey R, Harrison B, Geisinger ML, et al. COVID-19 among dentists in the United States: A 6-month longitudinal report of accumulative prevalence and incidence. J Am Dent Association. 2021;152(6):425–33.
Gómez-Ochoa SA, Franco OH, Rojas LZ, Raguindin PF, Roa-Díaz ZM, Wyssmann BM, et al. COVID-19 in health-care workers: a living systematic review and meta-analysis of prevalence, risk factors, clinical characteristics, and outcomes. Am J Epidemiol. 2021;190(1):161–75.
Bani Hani A, Alaridah N, Abu Abeeleh M, Shatarat A, Rayyan R, Kamal A, et al. Medical students and risk of COVID-19 infection: A descriptive cross-sectional study from the University of Jordan. Annals Med Surg. 2021;70:102775.
Zaher K, Basingab F, Alrahimi J, Basahel K, Aldahlawi A. Gender Differences in Response to COVID-19 Infection and Vaccination. Biomedicines. 2023;11(6).
de Lusignan S, Dorward J, Correa A, Jones N, Akinyemi O, Amirthalingam G, et al. Risk factors for SARS-CoV-2 among patients in the Oxford Royal College of General Practitioners Research and Surveillance Centre primary care network: a cross-sectional study. Lancet Infect Dis. 2020;20(9):1034–42.
Hewitt J, Carter B, Vilches-Moraga A, Quinn TJ, Braude P, Verduri A, et al. The effect of frailty on survival in patients with COVID-19 (COPE): a multicentre, European, observational cohort study. Lancet Public health. 2020;5(8):e444–51.
Pourmasumi S, Nazari A, Ahmadi Z, Kouni SN, de Gregorio C, Koniari I, et al. The Effect of Long COVID-19 Infection and Vaccination on Male Fertility; A Narrative Review. Vaccines. 2022;10(12):1982.
Williamson EJ, Walker AJ, Bhaskaran K, Bacon S, Bates C, Morton CE, et al. Factors associated with COVID-19-related death using OpenSAFELY. Nature. 2020;584(7821):430–6.
Stasi VD, Rastrelli G. The role of sex hormones in the disparity of COVID-19 outcomes based on gender. J Sex Med. 2021;18(12):1950–4.
Jones R, Davis A, Stanley B, Julious S, Ryan D, Jackson DJ, et al. Risk Predictors and Symptom Features of Long COVID Within a Broad Primary Care Patient Population Including Both Tested and Untested Patients. Pragmatic observational Res. 2021;12:93–104.
Sudre CH, Murray B, Varsavsky T, Graham MS, Penfold RS, Bowyer RC, et al. Attributes and predictors of long COVID. Nat Med. 2021;27(4):626–31.
Barbosa-Camacho FJ, García-Reyna B, Cervantes-Cardona GA, Cervantes-Pérez E, Chavarria-Avila E, Pintor-Belmontes KJ, et al. Comparison of Fear of COVID-19 in Medical and Nonmedical Personnel in a Public Hospital in Mexico: a Brief Report. Int J mental health Addict. 2023;21(1):383–94.
Fluck D, Rankin S, Lewis A, Robin J, Rees J, Finch J, et al. Comparison of characteristics and outcomes of patients admitted to hospital with COVID-19 during wave 1 and wave 2 of the current pandemic. Intern Emerg Med. 2022;17(3):675–84.
Antonelli M, Penfold RS, Merino J, Sudre CH, Molteni E, Berry S, et al. Risk factors and disease profile of post-vaccination SARS-CoV-2 infection in UK users of the COVID Symptom Study app: a prospective, community-based, nested, case-control study. Lancet Infect Dis. 2022;22(1):43–55.

No competing interests reported.

Investigating the Pre- and Post-COVID-19 Vaccination Infection Status of Iranian Dental Students: A Cross-Sectional Study

Status:

Version 1

Abstract

Introduction

Methods

Sampling Technique: Non-probability consecutive sampling.

Data Analysis

Ethical Considerations

Results

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1