A California nurse has tested positive for COVID-19 just eight days after receiving the vaccination.

ER nurse Matthew W., received the Pfizer vaccine on December 18, and took to his Instagram page to share a picture of the certificate he got after taking the vaccine.

‘Got my Covid vaccine! The 15 minutes afterward sitting around with a bunch of others while health care 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,’ Matthew wrote.

On Christmas Eve, Matthew, who works at two different hospitals in San Diego, began feeling unwell after working a shift in the COVID-19 unit. He told ABC 10 News that he first got the chills before coming down with muscle aches and fatigue. After he went for a test for COVID-19 on December 26, the result came back positive.

Speaking on the diagnosis, Dr. Christian Ramers, an infectious disease specialist with Family Health Centers of San Diego, said: ‘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.’

Ramers said it is possible that Matthew was infected before receiving the vaccine. He also said that he’s aware of other cases where health care workers became infected around the time they received the vaccine.

‘That first dose we think gives you somewhere around 50% and you need that second dose to get up to 95%,’ Ramers added.

According to a report, regulators of the Pfizer vaccine have found that the best immunity against coronavirus comes seven days after the second dose, which is given three weeks after the first, meaning there is a possibility that someone who had received the vaccine could still contract the virus within that time frame. All patients need two doses of the vaccine to achieve immunity.