SALEM — Nearly 4 in 5 coronavirus deaths in Oregon during the first four weeks of August were among unvaccinated or partially vaccinated individuals, according to new data released by the Oregon Health Authority.

And roughly 5 in 6 of the 51,391 known COVID-19 infections during the same period were among people who were unvaccinated or not fully vaccinated, according to a state report released Thursday, Sept. 2.

The share of so-called breakthrough cases and deaths among fully vaccinated Oregonians remains tiny compared to the 2.4 million Oregonians who were fully vaccinated as of Aug. 28, demonstrating the effectiveness of vaccines at preventing severe COVID-19.

Since the start of the pandemic, the state has identified 13,166 breakthrough cases, which is defined as a person who tests positive 14 days or later after receiving their full course of vaccinations, which is two shots of Pfizer-BioNTech or Moderna vaccine or one shot of Johnson & Johnson vaccine. That’s slightly more than one half of 1% who have been infected with the disease after being fully vaccinated.

The health authority report says 650 people with breakthrough cases have been hospitalized — 0.027% of vaccinated Oregonians. And the 113 Oregonians who died after a breakthrough case amounts to 0.0047% of those vaccinated.

“Both hospitalizations and deaths are extremely small in terms of percentage of those vaccinated,” said Chunhuei Chi, director of the Center for Global Health at Oregon State University. “That’s why we call the current surge a pandemic of the unvaccinated.”

But the Oregon Health Authority’s latest data also shows most of the fatalities among vaccinated people occurred in August, one of the state’s deadliest months since the start of the pandemic.

Before August, the state had identified only 43 fully vaccinated people who died with COVID-19. But in the first four weeks of August, the state tallied the deaths of 70 fully vaccinated people — a number that may not yet be complete, said Delia Hernández, a spokesperson for the health authority.

Those 70 deaths accounted for 22% of the 321 COVID-19 related fatalities between Aug. 1 and Aug. 28, Hernández confirmed.

Breakthrough cases have become a growing concern as the delta variant wallops the nation and most of the world. Although public health experts and epidemiologists say the vaccines offer enormous protection against hospitalization and death — even from delta — their effectiveness wanes over time.