A large nationwide study of more than 4 million people in New Zealand identified a statistically significant association in two adverse events following vaccination with Pfizer’s COVID-19 vaccine.
In the post-marketing safety study recently published in Springer, researchers examining 12 specific adverse events found an increase in myopericarditis during the 21-day period following both Pfizer vaccine doses. Myopericarditis describes two distinct inflammatory heart conditions that occur simultaneously, myocarditis and pericarditis.
The highest rate of myopericarditis was observed in the youngest participants under 39 years of age following the second vaccine dose—with an estimated five additional myopericarditis cases per 100,000 persons vaccinated regardless of age. Researchers also observed an increase following both vaccine doses in individuals aged 40 to 59.
“Our findings align with international postmarketing studies, case series reports, and cases detected through reports to New Zealand’s spontaneous system that identify an association between the BNT162b2 vaccine and myo/pericarditis, especially in younger people and after the second dose,” the researchers stated.
In addition to myopericarditis, the study found an increase in single-organ cutaneous vasculitis (SOCV) in the 20- to 39-year-old age group following the first vaccine dose. SOCV is a syndrome characterized by inflammation and damage to the skin's blood vessels without the involvement of other organ systems.
Study Methods
To carry out their study, researchers collected data from Feb. 19, 2021, at the beginning of the vaccine rollout, to Feb. 10, 2022, among 4,114,364 individuals aged 5 and older who received a first and second primary or pediatric dose of Pfizer’s COVID-19 vaccine. During the study period, 13,597 individuals were excluded after testing positive for COVID-19.
The researchers then compared the incidence rates of each outcome of interest for 21 days—the interval between first and second vaccine doses—following vaccination with Pfizer’s COVID-19 vaccine to the expected background incidence rate from a pre-vaccination period (2014 to 2019) to detect vaccine safety signals.
Outcomes of interest were identified from New Zealand’s National Minimum Data Set—a national data collection system for all public hospitalizations connected to a National Health Index number that allows researchers to link hospitalization with Pfizer vaccination records in the National COVID Immunisation Register.
The 12 adverse events analyzed included acute kidney injury, acute liver injury, Guillain-Barré syndrome, erythema multiforme, herpes zoster, SOCV, myopericarditis (includes all events coded as myocarditis, pericarditis, and myopericarditis), arterial thrombosis, cerebral venous thrombosis, splanchnic thrombosis, venous thromboembolism, and thrombocytopenia.
Outside of myopericarditis and SOCV, researchers identified no other statistically significant associations between Pfizer’s COVID-19 vaccine and other outcomes of interest for all ages combined. Unlike myopericarditis, SOCV has not been identified as an adverse reaction to Pfizer’s COVID-19 vaccine, and only a few case reports and reviews have been published in the literature.
Potential Study Limitations
The study had several potential limitations. Although many adverse events of special interest resulted in hospitalization, some conditions, such as herpes zoster, are typically treated in the primary care setting. Diagnoses of conditions following COVID-19 vaccination in the general setting were not included in the analysis and could be underestimated.
Using ICD-10-AM codes to identify outcomes of interest without conducting clinical record assessments could lead to potential misclassification, and changing diagnostic codes before the study period could overinflate or underestimate potential adverse events.
Healthy vaccinee bias could affect results when comparing observed adverse events among the vaccinated cohort with the background population, as healthier people are more likely to get vaccinated. Additionally, a risk period of one to 21 days may exclude potential adverse events beyond the time frame, according to the study.
Researchers Conclude Benefits of Vaccines Still Outweigh Risks
Despite the increased risk of myopericarditis observed during the study, researchers said the risk of myocarditis following SARS-CoV-2 infection is “substantially greater” than after COVID-19 mRNA vaccination, leading them to conclude the benefits of vaccination still outweigh the risks from the disease.
Yet experts acknowledge that myocarditis caused by a natural viral infection differs from that triggered by mRNA COVID-19 vaccination. As previously reported by The Epoch Times, although COVID-19 can cause myocarditis, the myocarditis developed by a healthy young person post-infection is extremely mild compared to the onset of myocarditis following COVID-19 vaccination.
According to pediatric cardiologist Dr. Kirk Milhoan, myocarditis caused by the COVID-19 vaccine differs from viral myocarditis because an infection of the heart isn't causing the damage. It's being damaged by the "spike protein that's cardiotoxic to the heart," which causes inflammation in the three main vessels of the heart by a different process.
"There’s a difference between the body encountering a virus naturally that causes myocarditis and actively giving the body something we know causes harm," Dr. Milhoan told The Epoch Times.
The New Zealand study adds to a growing body of evidence showing mRNA COVID-19 vaccination can trigger heart inflammatory conditions in young people.
