OLYMPIA–The Washington State Department of Health (DOH) is investigating reports of people in the state who tested positive for COVID-19 more than two weeks after being fully vaccinated. Scientists call these "vaccine breakthrough" cases, which are expected with any vaccine.

Large-scale clinical studies found that COVID-19 vaccines reduced the risk of getting COVID-19 in vaccinated people by up to 95% compared to people that did not receive the vaccine. However, the vaccines are not 100% effective in preventing infection. This means a small percentage of fully vaccinated people can be expected to still get COVID-19. These are identified as breakthrough cases.

Out of one million fully vaccinated individuals in Washington state, epidemiologists report evidence of 102 breakthrough cases since February 1, 2021, which represents .01 percent of vaccinated people in Washington. Breakthrough cases have been identified in 18 counties. The majority of those in Washington state with confirmed vaccine breakthrough experienced only mild symptoms, if any. However, since February 1, eight people with vaccine breakthrough have been hospitalized. DOH is investigating two potential vaccine breakthrough cases where the patients died. Both patients were more than 80 years old and suffered underlying health issues. Further investigation will help to identify patterns among people who have COVID-19 after vaccination, such as if a virus variant may have caused the infection.

"It is important to remember that every vaccine on the market right now prevents severe disease and death in most cases," said Umair A. Shah, MD, MPH, Secretary of Health. "People should still get vaccinated as soon as they are eligible, and encourage friends, loved ones, and co-workers to do the same."

DOH confirms a breakthrough case with a positive PCR test or Antigen test in a person more than two weeks after he or she has received their final dose of the COVID-19 vaccine. Additional investigations help determine clinical and outbreak information.

"Finding evidence of vaccine breakthrough cases reminds us that, even if you have been vaccinated, you still need to wear a mask, practice socially distancing, and wash your hands to prevent spreading COVID-19 to others who have not been vaccinated," said Secretary Shah.

The Department of Health will provide a regular report regarding vaccine breakthrough in Washington state beginning in late April.