Covid 19 coronavirus: Nurse tests positive days after vaccine - but that's what the experts expect

ER nurse Matthew announced he had received the vaccine on Instagram. Photo / Supplied

An emergency nurse in the United States has tested positive for Covid-19 just eight days after getting the vaccine - but experts aren't worried.

A Californian ER nurse who works at two hospitals in San Diego, identified as Matthew on social media, received the Pfizer vaccine on December 18, according to an Instagram post.

"Got my Covid vaccine!" he wrote.

"The 15 minutes afterwards sitting around with a bunch of others while healthcare workers asked us how we felt made me think of an opium den. I'll report back if I start to grow a third arm."

However, Matthew started feeling sick a week later on Christmas Eve with chills, muscle aches and fatigue after working a shift in one of the hospital's Covid-19 units, he told ABC 10 News.

On December 26, he tested positive for coronavirus, The Daily Mail reported.

Dr Christian Ramers, an infectious disease specialist with Family Health Centers of San Diego, told the network he isn't surprised and said the result is "not unexpected".

The ER nurse, pictured second from the left, started feeling sick about a week later. Photo / Facebook

"It's not unexpected at all. If you work through the numbers, this is exactly what we'd expect to happen if someone was exposed," he said.

Dr Ramers added Matthew could have been infected with coronavirus before he was vaccinated.

"We know from the vaccine clinical trials that it's going to take about 10 to 14 days for you to start to develop protection from the vaccine," Dr Ramers said.

The doctor added he was aware of other cases of healthcare workers becoming infected around the time they received the vaccine.

"That first dose we think gives you somewhere around 50 per cent, and you need that second dose to get up to 95 per cent," Dr Ramers said.

Matthew said his symptoms have improved and he is feeling better.