Covid-19 Vaccine

Vaccine's Second Dose More Likely to Cause Side Effects

The first health care workers to receive the coronavirus vaccine are now getting their second doses

NBC Universal, Inc.

David Flores, an emergency room nurse at UCSD, received the second dose of the Pfizer vaccine on Thursday. Unlike the first dose, this one came with side effects. 

“My hips were killing me,” Flores said. “I had a hard time sleeping because of that. I couldn't get comfortable. My back, knees, and ankles hurt.”

Flores said that a lot of his co-workers shared similar experiences. 

“It’s something that we observed from clinical trials,” said Dr. Edward Cachay, infectious disease specialist at UCSD. “When people receive that second dose, they are receiving the second booster to try and reach the maximum efficacy. So by boosting the immune system, in general people develop joint pains and low-grade fevers that usually last 24 to 48 hours.”

According to Pfizer, about 3.8% of their clinical trial participants experienced fatigue as a side effect and 2% got a headache. 

Moderna says 9.7% of their participants felt fatigued and 4.5% got a headache. 

But regardless of the side effects, Dr. Cachay says it is extremely important that patients get the second dose of the vaccine. 

“Whenever you receive the first shot, you are protected only approximately 51% , so you need that second dose to get that 95% against COVID-19," he said.

Despite the joint pain, Flores says there is no doubt he made the right decision in moving forward with the vaccine. 

“It’s the lesser of two evils,” Flores said. “Just being sick for a day or so and being either dead or being sick for months or days, is a pretty good trade-off.”

Dr. Cachay adds that patients don't reach maximum immunity until 10 to 14 days after the second dose. 

According to UCSD officials, they've already given the vaccine to approximately 10,000 workers. Many of whom have already started receiving the second dose.

They add, only 3% of employees have declined the vaccine. 

Contact Us