In a series of tweets, the Twitter CEO said he felt like he "was dying" and that a cousin of his in "peak health" suffered myocarditis, an inflammation of the heart which is listed as a possible side effect of some coronavirus vaccines.
"I had major side effects from my second booster shot. Felt like I was dying for several days. Hopefully, no permanent damage, but I dunno," Musk said in a tweet.
He added: "And my cousin, who is young & in peak health, had a serious case of myocarditis. Had to go to the hospital."
In a third post, Musk explained it was not his choice to get the second booster but was a requirement to visit a Tesla location in Berlin, Germany.
"Was required to visit Tesla Giga Berlin. Not my choice," he said.
In yet another post, Musk explained he had no issues with receiving the initial Johnson & Johnson vaccine or the first mRNA booster.
"I had OG C19 before vaccines came out and it was basically a mild cold. Then had J&J vaccine with no bad effects, except my arm hurt briefly," he tweeted.
The Tesla founder added: "First mRNA booster was ok, but the second one crushed me."
Musk's posts were in response to a Rasmussen Reports tweet that reported approximately 12 million people may have experienced "major side effects" after getting the vaccine.
According to the Centers for Disease Control and Prevention (CDC) cases of myocarditis are a "rare risk" for those who receive mRNA COVID-19 vaccines.
"These rare cases of myocarditis or pericarditis have occurred most frequently in adolescent and young adult males, ages 16 years and older, within 7 days after receiving the second dose of an mRNA COVID-19 vaccine (Pfizer-BioNTech and Moderna). There has not been a similar reporting pattern observed after receipt of the Janssen COVID-19 Vaccine (Johnson & Johnson)," the CDC says on its website.
The website adds: "CDC continues to recommend COVID-19 vaccination for everyone 6 months of age and older. The Advisory Committee on Immunization Practices (ACIP) and CDC have determined that the benefits (such as prevention of COVID-19 cases and its severe outcomes) outweigh the risks of myocarditis and pericarditis after receipt of mRNA COVID-19 vaccines."
Myocarditis is inflammation of the heart muscle and the CDC said preliminary data shows "most patients" ultimately recovered from their myocarditis.
"Preliminary data from surveys conducted at least 90 days after the myocarditis diagnosis showed most patients were fully recovered from their myocarditis," the CDC said.
Comment: The long-term data (should the CDC even deign to collect it) may show a much different picture. Myocarditis causes permanent damage to heart tissue.
It recommends all cases of myocarditis and pericarditis be reported to the Vaccine Adverse Event Reporting System (VAERS).
Federal law requires healthcare providers to report such issues to VAERS.
Musk has been repeatedly critical of the COVID pandemic and of Dr. Anthony Fauci, who oversaw the U.S. pandemic response under the Trump and Biden administrations as White House Chief Medical Advisor.
Comment: Another to come around is Scott Adams, who was vociferous in his support of the vax, because of his personal health issues. His characterization of "winning" and "losing" though, misses the point. No one "won" except Big Pharma.