(SACRAMENTO)

Donovan Nielsen had a sore arm. Nicholeth Santiago had one rough day of chills and muscle aches. David Tom Cooke had a mildly sore shoulder and a little fatigue. 

Three months after Donovan Nielsen was given the vaccine, he said, “Nothing has changed about my health … except I haven’t gotten COVID-19.”
Three months after Donovan Nielsen was given the vaccine, he said, “Nothing has changed about my health … except I haven’t gotten COVID-19.”

That was the range of reactions for some of the UC Davis Health front line workers who volunteered in Pfizer’s COVID-19 vaccine clinical trial – and learned recently that they received the vaccine. 

“What I felt was about the same as what you’d get from a flu shot,” said Nielsen, a clinical research coordinator in the UC Davis Medical Center Emergency Department. “It was all pretty minor. There was nothing to keep anyone from getting the vaccine.” 

Pfizer began telling trials participants whether they got the vaccine or the placebo when vaccines became available for frontline workers. Nielsen, Santiago, Cooke and many others have unknowingly carried the effects of the vaccines for months, and they have been barely noticeable – beyond their boosted immunity to COVID-19. 

Nielsen was the first of the 225 trial participants managed by UC Davis Health  to get an injection in August. He learned the vaccine and its impact have been with him for more than three months now. 

“Nothing has changed about my health after I received the vaccine,” Nielsen said, “except I haven’t gotten COVID-19. I didn’t feel anything different.” 

The varied and generally mild reactions of the UC Davis participants who spoke for this story are only a piece of the full picture of vaccine reactions. But according to data submitted to the U.S. Food and Drug Administration (FDA) on both the Pfizer-BioNTech and Moderna vaccines, their reactions are also very typical. 

“I was so happy. I felt like there was a big weight off my shoulders. I have a feeling of a little more safety now.”

— Nicholeth Santiago

Read about common COVID-19 vaccine myths 

More than 43,000 people took part in the Pfizer clinical trial. Moderna had about 30,000 volunteers in its trial. According to the FDA reports, the most common reactions for both vaccines were muscle aches, fatigue, headaches or chills. Smaller numbers of participants reported a low-grade fever. All the UC Davis Health trials volunteers we talked with compared their reactions with flu shots and said the side effects were no big deal. 

Vaccine reactions: Mostly minor

Most people in the national trials who had a reaction – and all the UC Davis participants in this story – felt them more after the second shot. Both the vaccines require two injections. Pfizer’s doses come three weeks apart. Moderna’s are given four weeks apart. 

Pfizer is only unblinding the trial for people as they would become eligible to get a vaccine in the tier system. All trials participants who got the placebo will get vaccinated as soon as their tier comes up. 

Santiago, also a clinical research coordinator in the UC Davis Medical Center Emergency Department, said her feelings when she learned she had been given the vaccine were something everyone should – and can – experience. 

“I was so happy,” she said. “I felt like there was a big weight off my shoulders. I have a feeling of a little more safety now.” 

She was not entirely surprised she received the vaccine considering her reactions. She was on the more intense side of the scale – but still nothing she couldn’t deal with.

“I thought it was important to have diversity among the participants and to be able to show African Americans they can trust this vaccine.”

— David Cooke

“The first dose was arm pain, like a regular vaccine,” she said. “The second dose was when I got instant muscle ache, a typical vaccine side effect. On top of that, later that night, I had the chills and I had muscle pain.” 

Her summary of her experience: A minor inconvenience. Nothing to stop anyone from getting vaccinated. If anyone is worried, she suggested scheduling a day off after the second dose, just in case. 

“It was super doable, and I wasn’t allowed to take pain relievers but everyone else can, if they want,” Santiago said. “It was all less than 24 hours. I hope people know they can be completely comfortable getting the vaccine. I know the process of research. It’s my career. I know how many people were in the trial. This is very safe.” 

An example of trust

Cooke, an associate professor and head of general thoracic surgery at UC Davis Health, said he volunteered for the trial to provide an example for anyone who might have doubts, and particularly as an example for people of color. 

“I’m a surgeon but I don’t like needles,” Cooke said. “But as an African American, I thought it was important to have diversity among the participants and to be able to show African Americans they can trust this vaccine.” 

He gives Pfizer credit for enrolling a diverse group of trial participants. 

“They understood the need to create a vaccine that is effective not just for one part of our community but for all our communities,” Cooke said. 

As for his reactions, they were so mild Cooke didn’t really notice them. It wasn’t until he learned he was given the vaccine that he thought more about them. 


David Tom Cooke volunteered for the clinical trial to be an example to people of color and to offer assurance they can trust the vaccine.

“It could have been normal fatigue from a long day in surgery,” he said. “That shows how much better than expected my reactions were. It was only when I think back now, I believe I had some extra tiredness and a slight headache.” 

That is part of the message he hopes people of color will hear. 

“Their concerns about the health care experience are warranted based on the historical relationship between health care and African American communities and institutional racism,” Cooke said. “But this time, I want them to be reassured. 

“I have the advantage of being in health care and working side by side with the people who ran the trial at UC Davis Health,” he said. “I trust them entirely. I trust this vaccine.” 

There is another side to the COVID-19 vaccine trials experience among UC Davis Health volunteers. Joseph Sison, a clinical professor of psychiatry, learned he received the placebo. 

“I wasn’t surprised,” he said, “because about a month ago I ended up getting COVID-19.” 

He has fully recovered from the disease, and he got his first vaccine dose. Now he jokes that he at least provided a valuable proof point. 

“I’m glad to have been part of the data that showed the vaccine is 95% effective, and that the science works,” he said. 

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