Rationale Recently, a CDC advisory Committee on Immunization Practices identified a likely association between the 2 COVID-19 mRNA vaccines from Pfizer-BioNTech and Moderna and cases of myocarditis and pericarditis. For the cardiovascular system, 4863 adverse events (AEs) were reported from the Pfizer vaccine. Common findings observed with vaccines under study were tachycardia(16.41%), flushing (12.17%), hypertension (5.82%), hypotension (3.6%), and increased heart rate (9.03%). In this study we characterized, classified, evaluate the dynamic of cardiac function and ECG abnormality after the Pfizer vaccine injection.

This is a prospective cohort study. All participants aged 13-18 years old and above who visited the second dose Pfizer covid-19 vaccine injection to determine cardiac manifestation.

Methods for analyzing research data The data will be collected from students enrollment at Kong thabbok upatham changkol kho so tho bo school and Wachirathamsatit school. The participant's history, physical exam, and laboratory data will be reviewed and data will be extracted based on the case record form (CRF). All data will be stored securely and analyzed using the SPSS® Statistics Version 23 developed by IBM®. Data entry will be carried out using coding and verification. Quantitative data will be expressed as mean with standard deviation (SD) or median (IQR) and qualitative data will be presented as a number of observations with percentage (%). Descriptive statistics will be used to summarize the baseline values and demographic data.

All p-values will be derived using the 2-tailed testing, and statistical significance will be set at 0.05 probability. All the categorical variables will be analyzed using the chi-square (x2) or Fisher's exact test whichever is appropriate. Normality of the distribution will be tested for the continuous variable using the Kolmogorov- Smirnov test. All the variables with normal distributions will be compared using the independent t-test and will be reported as mean ± standard deviation (SD). The variables that do not pass the normality test will be compared by means of the Mann-Whitney U test and will be reported as the median and interquartile range (IQR).

Data Collection Methods

1. Participants' demographics will be collected at baseline using case record form.
2. Laboratory tests include: at 3 clinical visits (Baseline, Day3, Day7 and Day 14 (optional if have cardiac manifestation) after 2nd dose of Pfizer COVID-19 vaccine) 2.1. Cardiac biomarker (Troponin-T, CK-MB) 2.2. Echocardiography 2.3. ECG (Electrocardiography)

After getting approval from the Ethics Committee and before the start of the trial, the study team informed the interesting participants about the study by invitation letter with ZOOM or line meeting. Informed consent printed to the parents who interested in this project and bring to the team investigator before enrollment. A contact address and phone number will be provided for the interesting participants to call for more information about the study.

Inclusion Criteria:

1. Age 13-18 years old
2. Both males and females
3. Received 1st dose Pfizer COVID-19 vaccine injection

Exclusion Criteria:

1. Unable to obtain written informed consent from the participants or their legal representatives
2. History of cardiomyopathy, tuberculous pericarditis, and constrictive pericarditis
3. Severe allergic reaction to COVID-19 vaccine

Student age 13-18 who received 1st dose of pfizer COVID-19 vaccine from

1. Kong thabbok upatham changkol kho so tho bo school
2. Wachirathamsatit school

Data or leftover specimens will be shared for future study ONLY subjects who consent allow using their specimens. Sharing will be done without specimen identification.

2 years after publication