The Oregon Health Authority reported a small number of cases Thursday where Oregonians who had received their full vaccinations later contracted COVID-19.The state defined the “breakthrough” cases as instances where a person had received their final dose of vaccine and then contracted COVID-19 at least 14 days later.Of the more than 700,000 Oregonians who are now fully vaccinated, health officials identified only 168 breakthrough cases as of April 2. That is equivalent to roughly 0.0002% of that fully vaccinated group. Three of those 168 died.“It’s a reminder that while the Pfizer, Moderna and Johnson & Johnson COVID-19 vaccines are all highly effective at preventing severe COVID-19 illness and death, no vaccine is 100% effective, and vaccine breakthrough cases will occur,” the Oregon Health Authority said in a statement.A vile of Pfizer vaccine and syringe.Kristyna Wentz-Graff / OPBThe cases occurred across the state in 25 counties. According to health officials, many of the people who had breakthrough cases experience asymptomatic infections. A small percentage of the cases became ill enough to require hospitalization, and three people died. The state said most of the cases occurred in people who were older than 65 and who had underlying health conditions.“State and local epidemiologists are continuing to track and investigate vaccine breakthrough cases and are working closely with the Centers for Disease Control and Prevention to collect information that may provide insight into characteristics associated with vaccine breakthrough,” the health authority said in its statement.Oregon is not alone in seeing small amounts of COVID-19 cases after vaccination. Washington state reported a similarly small amount of breakthrough cases at the end of March.Health officials said people who receive vaccination can limit the risk of breakthrough cases by continuing to practice basic health safety even after being vaccinated, such as wearing masks when around other people, socially distancing and avoiding large gatherings.