Sen. Ron Johnson, R-Wis., has sent letters to the CEOs of Pfizer and Moderna seeking answers about adverse reactions to the COVID-19 vaccine following a June 28 press conference with affected individuals. 

The conference in Milwaukee included stories from five people, four of whom were women, from across the country who experienced adverse reactions to the vaccines and experienced "refusal or reluctance" from their doctors to acknowledge that their symptoms might be tied to the vaccine, according to Johnson's letters.

"I do want to be clear at the outset, to a person, we are all pro-vaccine," Johnson said in a statement. "Personally, I’ve had every flu shot since at least the swine flu. I’m current in all of my other vaccines. I was a huge supporter of Operation Warp Speed. I’m happy to acknowledge that over 300 million doses of the vaccine have been given to the U.S., and for most people, the vast majority of people, the vaccine has been administered with little or no side effects."

He added that he personally believes "the vaccine has saved countless lives … and has contributed to the end of the pandemic, which is what everybody in the world wants," but "people that are trying to tell the truth" about their experiences with the vaccines "are having a hard time getting their truths communicated without being vilified, without being ridiculed, without being censored."

The Wisconsin senator noted that some adverse reactions were detailed in Pfizer's and Moderna's Food and Drug Administration (FDA) emergency use authorization (EUA) memorandums following early clinical trials. 

Those reactions included nervous system disorders and musculoskeletal and connective tissue disorders for the Pfizer EUA memo. The Moderna EUA memo included reactions such as nervous system disorders, vascular disorders and musculoskeletal and connective tissue disorders, according to Johnson's letter. 

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Pfizer and Moderna did not immediately respond to inquiries from Fox News about Johnson's letters.

Sheryl Ruettgers, one of the five speakers at the Milwaukee press conference, said that she is pro-vaccine but believes people should be aware of the risks of a bad reaction.

"My neurological symptoms have left me barely able to function some days, and the internal tremors create a type of fatigue that I have never experienced before," she said. "I am unable to fully participate in the activities I enjoyed before being vaccinated. My life has been negatively altered as a result of my vaccine. Will I get better? Will I develop Parkinson’s or MS or ALS or another neuro-degenerative disease? I don't know, and my doctors can’t tell me if they know. So what do I want? I want our neurological injuries to be recognized and acknowledged by the CDC and the FDA."

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Candace Hayden, who also described herself as pro-vaccine, had a similar experience.

"Before this, I was healthy. I was active and self-sufficient. I fear my diminished quality of life is my new normal," she said at the conference. "Will I ever run again? Will I ever ride my bike? I would give anything to get in my car and just drive it. My greatest fear is for others like Maddie, the children, those that are younger that don’t have a voice, that can’t tell you how they’re feeling, that don’t understand why their legs are no longer working."

Johnson noted that many of those who experienced bad side-effects from the vaccine have joined together on Facebook groups to detail their experiences, but their posts are being labeled as potentially misleading information. 

The senator is asking Pfizer and Moderna to list all adverse reactions to the vaccine since their EUAs and how frequently they occurred and detail what each company has done to assist individuals who have experienced adverse reactions, among other requests.

More than 150 million U.S. residents, or more than 60% of the country's population, have received at least the first dose of the COVID-19 vaccine, there are rare instances in which people experience bad reactions, according to the Centers for Disease Control and Prevention. In clinical trials, the Moderna vaccine was 94.1% effective in preventing COVID-19, and Pfizer was 95% effctive.

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The National Institutes of Health (NIH) in April launched a clinical trial to better understand allergic reactions related to the Moderna and Pfizer-BioNTech COVID-19 vaccines

The trial, which involves 3,400 adults, 60% of whom have a history of severe allergic reactions or a diagnosis of mast cell disorder, considers the biological mechanism behind the reactions to see if a genetic pattern or other factors can better predict who is at risk of a reaction.

The spike protein associated with the mRNA vaccines can possibly result in an "extremely rare" adverse event, such as an autoimmune reaction, Dr. Anthony Fauci, the nation’s leading infectious disease expert, said on May 25. 

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Fauci, who was testifying before a House Appropriations subcommittee on the agency’s budget request said the number of overall adverse events among the millions of administered vaccine doses is remarkably low, but immunologists are "obviously are interested in whether or not there is anything about the spike protein that would trigger something such as an autoimmune reaction that might give you a deleterious effect," he said.

The CDC is also investigating rare reports of a heart issue called myocarditis among adolescents and young adults who received COVID-19 vaccinations. Dr. Richard Besser, former acting head of the agency and CEO of the Robert Wood Johnson Foundation, says there is no clear link yet to the vaccines and is encouraging parents to keep getting kids vaccinated.

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Ben Haynes, a CDC spokesperson, told Fox News in a May 25 statement that "myocarditis and pericarditis are side effects that can be seen following a viral infection and other types of vaccination. Reported cases appear to be mild and often go away without requiring treatment."

"These reports are rare given the number of vaccine doses administered, and CDC and FDA will continue to monitor and evaluate reports of myocarditis/pericarditis occurring after COVID-19 vaccination," he continued. "Healthcare providers should report all cases to VAERS. CDC continues to strongly recommend COVID-19 vaccination for individuals 12 years of age or older given the risk of COVID-19 illness and related, potentially severe, complications. Getting vaccinated is the best way to protect you and your family from COVID-19."

Fox News' Alexandria Hein and Kayla Rivas contributed to this report.