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(NEXSTAR) – Epidemiologists in Washington state have reported evidence of at least 102 fully vaccinated people testing positive for COVID-19 since the beginning of February, the state’s health department confirmed Tuesday.

The dozens of so-called “vaccine breakthrough” cases have prompted a Washington State Department of Health investigation, but officials say the news is not unexpected.

Since the vaccines are not 100% effective, experts say there will be a small number of people who get vaccinated but still test positive for the virus, what’s known as a breakthrough case.

The vaccine breakthroughs are expected, according to the DOH, and the 102 people represent just .01% of the 1,000,000 fully vaccinated Washingtonians.

Symptoms and breakthrough cases

While the majority of breakthrough cases resulted in only mild symptoms, the DOH noted that eight people were hospitalized and two – both over the age of 80 and with underlying conditions – died.

“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,” DOH officials said in a news release.

The breakthrough cases were confirmed with a positive PCR or Antingen test administered at least two weeks after the final COVID vaccine dose.

“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 Umair A. Shah, MD, MPH, Secretary of Health.

The DOH said it will continue to update its findings in a regular report on vaccine breakthrough starting in late April. 

“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.”

Other states report breakthrough cases

Washington is not the only state to report such cases.

Earlier this month, the Hawaii Department of Health announced three cases in which a fully-vaccinated person still contracted COVID-19. A partially vaccinated resident also caught the U.K. variant.

In one of the cases, the DOH said a healthcare worker traveled one month after receiving both vaccine doses. The person and their travel partner had no symptoms and took the pre-travel test to come home. They did not get the test results until they landed, where they learned they were positive for COVID-19. Contact tracing revealed no one else was infected.