1 / 10The story of an emergency room nurse who tested positive for COVID-19 after getting the vaccine is a reminder that hand washing, social distancing and masks are still going to be crucial in 2021.2 / 10Matthew W., a 45-year-old nurse in San Diego, received the Pfizer vaccine Dec. 18 and told ABC News San Diego affiliate KGTV that the only vaccine side effect he experienced was arm soreness.3 / 10Six days later, after working a shift in the COVID-19 unit, Matthew had chills, muscle pain and fatigue. A drive-up hospital test confirmed he was positive for COVID-19.4 / 10The scenario isn't unexpected, Dr. Christian Ramers, an infectious disease specialist with Family Health Centers of San Diego, told KGTV.5 / 10Patients don't immediately develop COVID-19 protection after being vaccinated.6 / 10'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,' Ramers said.7 / 10Even after those 10 to 14 days, patients still need a second vaccine dose for full protection.8 / 10 'That first dose we think gives you somewhere around 50%, and you need that second dose to get up to 95%,' Ramers added.9 / 10Another possibility: Since the incubation period for COVID-19 can be as long as 14 days, it's also possible that Matthew was infected prior to receiving the vaccine on Dec. 18.10 / 10Both potential scenarios are a reminder that vaccines aren't a panacea. Instead, experts say, stemming the pandemic will take time and continued adherence to fundamental public health practices like social distancing, masks and hand washing.