Fort Worth, Texas,
10:58 AM

Cook Children’s Employee Shares Her Experience in COVID-19 Vaccine Trial

Christi Thornhill’s willingness to participate in a COVID-19 vaccination trial was driven by both a professional and personal conviction. As a seasoned nurse practitioner and director of trauma services at Cook Children’s Medical Center, she thought it important to do whatever she could to contribute to the cure. Personally, she was motivated by thoughts of her friends who have been deeply impacted by the virus.

“I thought participating was important,” Thornhill said. “Number one, we need a vaccine to be able to save people’s lives. I’m in health care, so I just felt like it was the right thing to do. I also have friends who have lost family members and people that I know personally that have had COVID, and they were scared because they had underlying health conditions and some of them had children that were scared.”

In August, Thornhill joined Moderna’s mRNA-1273 vaccine trial after volunteering through the COVID-19 Prevention Network (CoVPN). The trial, called the COVE study, is a cooperation between Moderna and the National Institutes of Health (NIH). Thornhill received the first of two shots on Sept. 18 following a multi-hour screening and medical workup. At that time she did not know if she received a placebo or the actual immunization. As part of the trial, Thornhill tracks her temperature, reactions, health changes and any symptoms she experiences in an online diary application.

“The night of my first shot I started my first entry into the online diary app,” Thornhill said. “That week I had about a day and a half of tenderness at the injection site. It was warm to the touch and tender, very much like my flu shot in some years.”

A member of the research team following Thornhill periodically calls her to check in on her post-shot status. It wasn’t until her second shot on Oct. 16 that Thornhill experienced symptoms that led her to believe she received the immunization, not a placebo.

“That night, about three hours after getting the second shot, I was having dinner with my husband and, all of a sudden, I just didn’t feel well,” she said. “It wasn’t overwhelming but my husband looked at me and knew something wasn’t right.”

Thornhill was experiencing pain in her arm, body aches, joint pain and a low-grade fever. The symptoms persisted the next day, a Saturday, so she took the weekend to rest. By Sunday, her symptoms were gone and she was back to feeling like herself.

“I think my symptoms were very similar to what we see when we give kids immunizations,” she explained. “They’re fussy and don’t feel well but usually within a day or two that resolves, and it did for me. I’m pretty sure I received the actual vaccine, because I don’t think a placebo would do that.”

Thornhill advises those who get the vaccine to consider getting the second shot just before a weekend or when they have a few days off to recover in case their reaction is similar to hers.

Novel Vaccine For A Novel Virus

One of the unknowns about the new vaccine is whether or not it provides long-term protection against the virus. It remains to be seen if a COVID-19 vaccine will be once and done or become an annual immunization, much like the flu shot. In March, Thornhill will return to the research center for tests to determine if her immune system created COVID-19 antibodies following her shots, and she’ll be followed for the next two years to see how long any produced antibodies persist. At some point in the study, she’ll know for sure if she was given the placebo or the immunization.

Some people question the safety of a novel immunization for a novel virus. Thornhill said she trusts the Food and Drug Administration (FDA) and their approval of the vaccine.

“I think it’s such an individual decision and you have to think about your own circumstances,” she said. “I trust the FDA is going to do the right thing. I believe in vaccinations. I understand herd immunity and the science behind it and why we do it.”

Unlike typical vaccines, the NIH-Moderna immunization is made of messenger ribonucleic acid (mRNA)—not a weakened or inactive virus-—so there is no risk of being infected with the coronavirus from the shots. To make the vaccine, scientists isolated a protein within COVID-19 and encoded it into the mRNA instruction molecule. Once injected into an individual, this genetic code instructs immune cells to make copies of the same protein so that they can recognize the virus should a person come in contact with it and produce antibodies to fight it. As of late October, more than 25,500 COVE Phase 3 study participants have received their second vaccination, according to Moderna’s website. The NIH reports that results for the vaccine show a 94.5 percent efficacy rate.

Pfizer and BioNTech are also conducting a vaccine trial using mRNA. Both the NIH-Moderna and Pfizer/BioNTech vaccines are awaiting approval by the FDA. If approved, distribution is expected to begin within weeks.

Thornhill has no regrets when it comes to her trial participation.

“I’m hoping the FDA gets these approved and gets them out there pretty quickly and that they’re effective so that we can have some semblance of normalcy back in our lives,” she said. “A vaccine would take away that fear of losing somebody or having long-term health issues from a virus that we still don't understand all the ramifications of or the long-term effects.”

For more information about vaccines and COVID-19, visit For the latest on how COVID-19 is impacting kids and Cook Children’s work to protect them, visit the medical center’s newsroom at