A United States-based nurse has tested positive for the coronavirus a week after receiving a shot of Pfizer vaccine. The nurse identified as Matthew W works as an ER nurse at two hospitals in San Diego. On December 18, he received the vaccine shot, which left his arm sore for a day.

According to ABC news, the 45-year-old  experienced muscle aches and fatigue before testing positive for the deadly virus.

Dr. Christian Ramers, a member of the clinical advisory panel for the US’ vaccination plan, said, “It is possible that Matthew was infected before receiving the vaccine, as the incubation period may be as much as two weeks. Additionally, we know from the vaccine clinical trials that it is going to take about 10 to 14 days to develop protection from the vaccine.”

Ramers said there have been several other local cases where the health care staff got infected after receiving the vaccine.

“All cases illustrate the fact that results aren’t immediate. Even after you start receiving some protection, it won’t be full protection,” Ramers said.

He added that the first dose of vaccine only ensures around 50 percent protection against the virus, which can be prevented up to 95 percent with the second shot.