Introduction

Myocarditis, the inflammation of heart muscle tissue, has emerged as a significant concern in relation to mRNA COVID-19 vaccines. While rare, this condition and its related variant pericarditis (inflammation of the lining around the heart) have been documented following vaccination, particularly in younger males. The Centers for Disease Control and Prevention (CDC) and Food and Drug Administration (FDA) play critical roles in monitoring vaccine safety and communicating potential risks to healthcare providers and the public. However, recent investigations suggest that these agencies may have delayed warning the public about these potential complications despite early awareness of the risks.
 

Background

Understanding Myocarditis and Pericarditis

Myocarditis involves inflammation of the heart muscle, while pericarditis affects the lining outside the heart. Myopericarditis occurs when both conditions present simultaneously. These inflammatory conditions typically develop in response to an infection or other triggers, and while generally rare following vaccination, they have been observed with sufficient frequency to establish a causal relationship with mRNA COVID-19 vaccines manufactured by Moderna and Pfizer-BioNTech.
These conditions most frequently affect adolescent and young adult males within seven days after receiving the second dose of an mRNA vaccine, though cases have also been documented in females, other age groups, and after different doses. Most patients experiencing myocarditis after vaccination have seen their symptoms resolve by hospital discharge.
 

Early Awareness Timeline

The timeline of awareness regarding myocarditis risks began much earlier than public warnings would suggest. On February 28, 2021, an Israeli Ministry of Health official contacted the CDC and FDA about 40 cases of myocarditis and other heart-related ailments observed in young people who had received the Pfizer vaccine. Israel, which had achieved a much higher vaccination rate than the United States at that time, provided early warning signs that American health officials acknowledged but did not immediately act upon.
Approximately ten days after the Israeli warning, an FDA official drafted a response noting “limitations of passive surveillance” and “incomplete data” that made it “challenging to assess causation.” U.S. officials subsequently requested additional data from their Israeli counterparts.
 

Senate Investigation Findings

 

According to a 54-page interim report from Senator Ron Johnson’s office, top federal health officials actively took steps to “delay warning the public” for months in 2021 about the potential risks of heart-related complications from mRNA COVID-19 vaccines. Senator Johnson, who chairs the Senate Permanent Subcommittee on Investigations, has conducted extensive oversight into the government’s pandemic response, sending more than 70 oversight letters since 2021.

The report, based on 2,473 pages of records obtained via subpoena, presents evidence that “the Biden administration’s efforts to downplay and delay warning the public about the risks of myocarditis associated with the mRNA COVID-19 vaccines” continued for several months despite mounting evidence.
Internal Deliberations and Decision-Making

By mid-April 2021, a Defense Department contractor delivered a presentation to the COVID-19 Vaccine Safety Technical (VaST) working group concluding “there is a high likelihood that cardiac symptoms following COVID-19 vaccination represent a hypersensitivity eosinophilic myocarditis.” By this time, more than 158 cases of myocarditis, pericarditis, or myopericarditis had been reported to the Vaccine Adverse Event Reporting System (VAERS).

In May 2021, as the COVID-19 vaccine received approval for adolescents, members of VaST “felt that information about reports of myocarditis should be communicated to providers.” Health officials began deliberating the release of a draft National Health Alert Network (HAN) warning about myocarditis and pericarditis side effects.

Internal communications obtained through investigation reveal the hesitancy to issue formal warnings. On May 25, 2021, CDC official Dr. Sara Oliver wrote to Moderna: “The pros and cons of an official HAN are what the main discussions are right now. I think it’s likely to be a HAN since that is CDC’s primary method of communications to clinicians and public health departments, but people don’t want to appear alarmist either.”

A day later, then-FDA commissioner Dr. Janet Woodcock emailed then-CDC director Rochelle Walensky expressing that the FDA opposed issuing the warning as drafted. Other officials raised similar concerns, with Peter Marks, then-director of the Center for Biologics Evaluation and Research, specifically noting that “myocarditis and pericarditis have not actually signaled.”'

Rather than issuing the HAN, the CDC instead posted a notice on its website on May 28, 2021, acknowledging “increased cases of myocarditis and pericarditis” following mRNA vaccination while continuing to recommend immunization for those 12 and older. By this point, VAERS reports had increased to 752 cases of these cardiac conditions.

It wasn’t until June 25, 2021—nearly four months after the initial alert from Israeli officials—that the FDA finally updated the labels on Pfizer and Moderna vaccines to note the risk of myocarditis and similar complications.
 

Health Risks and Implications

The delay in warning the public about potential myocarditis risks raises serious questions about health implications, particularly for young Americans. According to the Senate report, “the Biden administration opted to withhold issuing a formal warning to the public for months about the safety concerns, jeopardizing the health of young Americans.”

VAERS data indicates that as of April 25, 2025, there were 38,607 deaths and more than 1.6 million adverse events worldwide associated with COVID-19 vaccinations. Of these deaths, 25% occurred on days 0, 1, or 2 following injection—a striking statistic compared to the 2,663 deaths reported to VAERS in association with flu vaccines over a 35-year period.

While these statistics reflect all reported adverse events and not just myocarditis cases, they underscore the scale of potential safety concerns that critics argue should have prompted more timely warnings.
 

Guidance for Clinicians

The CDC now provides specific guidance for healthcare professionals regarding myocarditis and pericarditis following COVID-19 vaccination:

All cases should be reported to the Vaccine Adverse Event Reporting System (VAERS).

Clinicians should consider myocarditis and pericarditis in persons with acute chest pain, shortness of breath, or palpitations, particularly in adolescents and young adults. Younger children may present with non-specific symptoms including irritability, vomiting, poor feeding, fast breathing, or lethargy.

Initial evaluation should include an electrocardiogram (ECG), troponin level, and inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate.

Consultation with cardiology specialists is recommended for suspected cases to assist with cardiac evaluation and management.

Evaluation should rule out other potential causes of myocarditis and pericarditis, including acute COVID-19 illness or other viral infections.

Despite these concerns, COVID-19 vaccination continues to be recommended for everyone aged six months and older in the United States, with guidance that people should stay up to date with vaccinations.

Conclusion and Call for Transparency

The Senate report concludes that “the full extent of the Biden administration’s failure to immediately warn the public about all COVID-19 vaccine adverse events must be completely exposed.” It emphasizes that information developed by federal health agencies belongs to the American people and “should be made fully and transparently available.”

Senator Johnson’s report argues that the delayed warnings about myocarditis and the apparent downplaying of vaccine health risks “jeopardized the public’s health,” particularly for young Americans. As oversight continues and previously withheld documents become available, the Senate Permanent Subcommittee on Investigations promises to “provide transparency and let the American public see what is their right to see.”

The timeline of awareness and delayed public communication regarding the risk of myocarditis and pericarditis following mRNA COVID-19 vaccination raises important questions about accountability and transparency in public health messaging during critical phases of the pandemic response. The balance between preventing unnecessary alarm and providing timely safety information remains a complex challenge for health officials, but one that directly impacts public trust in health institutions and vaccination programs.