BREAKING COVID-19 News! Thailand Study Finds That Homologous Vaccination With Pfizer’s BNT162b2 Increases Risk Of Myocarditis And Pericarditis!

COVID-19 News: In the ongoing global battle against the COVID-19 pandemic, vaccination has been a critical weapon, with billions of doses administered worldwide. Among these, the Pfizer’s BNT162b2 mRNA vaccine has played a pivotal role in numerous vaccination campaigns, claiming to offer substantial efficacy against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. However, a recent groundbreaking study covered in this COVID-19 News report conducted by researchers at Prince of Songkla University in Hat Yai -Thailand, National Health Security Office, Lak Si-Thailand and National Science and Technology Development Agency-Thailand has brought to light potential risks associated with homologous vaccination with BNT162b2, specifically noting an increased incidence of myocarditis and pericarditis, particularly among adolescent males.


Homologous Vaccination With Pfizer’s BNT162b2
Increases Risk Of Myocarditis And Pericarditis

Background
As of June 2023, more than 13 billion doses of COVID-19 vaccines have been administered globally, with mRNA vaccines like BNT162b2 and mRNA-1273 gaining widespread acceptance. While these vaccines have proven effective, large-scale studies across various countries have identified an increase in myocarditis and pericarditis cases, particularly in younger populations, predominantly male adolescents. The Thailand study seeks to address the gaps in existing data, especially in low- and middle-income countries, and focuses on both homologous and heterologous vaccination strategies.
 
Vaccination Landscape in Thailand
Thailand's vaccination strategy reflects a diverse approach, relying primarily on heterologous prime-boost combinations due to the availability of different vaccines at different times. The national vaccination campaign, initiated on February 28, 2021, prioritized adults and older individuals, utilizing vaccines like CoronaVac (Sinovac) and ChAdOx1 (AstraZeneca). Subsequently, the BBIBP-CorV (Sinopharm) vaccine was introduced, followed by the BNT162b2 vaccine for children and adolescents aged 5–18 years. This resulted in two primary vaccine regimens: the homologous three-dose 3 × BNT162b2 and the heterologous three-dose 2 × BBIBP-CorV/BNT162b2 series.
Methods and Study Design
To investigate the incidence rate of myocarditis and pericarditis, researchers employed a historical control cohort using data from Thai national vaccine and insurance claims databases. The study period ranged from August 2021 to September 2022, tracking the incidence of these conditions within the <40-year-old national population. Non-immunized individuals from August to October 2019 served as the reference group. The analysis included both homologous (3 × BNT162b2) and heterologous prime-boost (2 × BBIBP-CorV/BNT162b2) vaccine regimens.
 
Results and Patient Characteristics
The study identified 215 cases of myocarditis in the homologous 3 × BNT162b2 cohort, 5 cases in the heterologous 2 × BBIBP-CorV/BNT162b2 cohort, and 115 cases in the non-immunized population. The sex-specific incidence rate ratios (IRRs) indicated a notable increase in the risk of myocarditis after homologous vaccinatio n, particularly in adolescent males. However, the risk was not significant after heterologous vaccination. Pericarditis risks were also elevated in males after homologous vaccination.
 
Patient characteristics revealed that the homologous vaccination cohort (n = 7,594,965) was larger than the heterologous vaccination cohort (n = 2,914,643) at both time points. Female vaccine recipients outnumbered male vaccine recipients in all cohorts, with the 18–40-year age group being the largest in the heterologous vaccination, SARS-CoV-2 infection, and reference cohorts. The 12–17-year age group was the largest in the homologous vaccination cohort. The interval between doses was shorter in the heterologous vaccination group than in the homologous vaccination group.
 
Overall, there was a significant increase in the incidence of myocarditis after homologous 3 × BNT162b2 vaccination, with IRRs of 3.09 (95 % CI: 1.61 - 5.93) in females and 7.43 (95 % CI: 3.11 - 17.73) in males. Considerable heterogeneity (I2 > 50 %) was observed among the different age groups of males and females.
For the primary series of the BNT162b2 vaccine, the subgroup at the greatest risk of myocarditis was adolescent males who received the second dose of the homologous BNT162b2 vaccine, exhibiting an IRR of 22.96 (95 % CI: 14.32 - 36.82). For the booster dose, the 95 % CIs of the IRRs were wider than those of the primary series due to a considerable reduction in sample size. However, the IRRs in males were significantly increased after vaccination, with an overall IRR of 14.26 (95 % CI: 2.12 - 95.95).
 
Discussion and Comparative Analysis
The study findings align with global trends, indicating an increased risk of myocarditis and pericarditis, especially among male adolescents, following BNT162b2 vaccination. The risk after the third dose was significantly higher in males, while the risk in females and children aged 5 - 11 years was comparatively lower. Notably, the study observed a reduced risk of myocarditis in children aged 5 - 11 years after the first dose, suggesting a lower susceptibility in this age group.
Comparisons with a reference population from the pre-COVID-19 period revealed a higher incidence of myocarditis and pericarditis after SARS-CoV-2 infection, emphasizing the protective benefits of vaccination despite the observed risks. Additionally, the study highlighted potential differences in risk between mRNA vaccines, with BNT162b2 showing a higher incidence compared to the inactivated virus vaccine BBIBP-CorV.
 
Limitations and Considerations
While the study provides valuable insights, limitations include the absence of data on immunogenic background and potential confounders such as health insurance status. The study's reference population period was relatively brief, limiting adjustments for seasonality and annual trends. Additionally, the analysis focused on symptomatic cases requiring hospitalization, potentially underestimating incidence rates in vaccinated groups.
 
Conclusion and Implications
In conclusion, the Thailand study adds crucial information to the global discourse on COVID-19 vaccination risks. The increased risk of myocarditis following homologous BNT162b2 vaccination, especially in males, underscores the need for careful consideration in vaccination strategies. The study's findings support ongoing efforts to balance the benefits of vaccination against potential risks, particularly in specific demographic groups. Further research is warranted to explore the underlying mechanisms and assess the long-term outcomes of myocarditis and pericarditis post-vaccination, emphasizing the importance of continuous monitoring and adaptation in public health strategies.
This comprehensive exploration of Thailand's study on COVID-19 vaccine-induced risks serves as a valuable contribution to the evolving understanding of vaccine safety, offering insights that can inform global vaccination strategies.
 
The study findings were published in the peer reviewed journal: Vaccine )Science Direct by Elsevier)
https://www.sciencedirect.com/science/article/pii/S0264410X24000264
 
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