The Delta variant of the coronavirus, which can spread more easily and cause more severe illness, has been detected in Hawaii in a person who was fully vaccinated, according to the state Department of Health.

The variant was detected in a specimen from an Oahu resident who traveled to Nevada in early May. In addition to receiving two doses of a COVID vaccine prior to travel, the person, who is not being identified, tested negative for COVID prior to returning to Hawaii.

Several days after returning to the state, the person developed mild symptoms consistent with a COVID infection and subsequently tested positive for the virus. There is no evidence that the Hawaii resident passed on the virus, and household members and close contacts were quarantined.

Acting state epidemio­logist Sarah Kemble said Monday during a news conference that most members of the infected resident’s household had been fully vaccinated, which likely helped stop the virus from spreading.

“So we have an example here of why even though a vaccine isn’t 100% (effective) every time, it is still incredibly important and effective at slowing the spread in these novel variants,” she said.

The Pfizer-BioNTech and Moderna vaccines have shown to be 94% to 95% effective at preventing symptomatic COVID infections and highly effective at stemming the spread of the virus. The Johnson &Johnson vaccine has been shown to be less effective. But all three vaccines can prevent serious illness, hospitalization and death, even when there is a “breakthrough case.”

The Delta strain of COVID-19 was first detected in India, where its rapid spread set off a public health crisis in April and May. The majority of the country remains unvaccinated. The variant has spread to dozens of countries and now comprises 91% of new cases in the U.K., where health officials believe it has pushed up case counts within the country.

The Delta variant now comprises about 6% of the cases in the United States. Kemble said a primary concern about the variant is its tendency to become a dominant strain, suggesting that it’s more contagious.

There are also reports that the Delta variant produces a higher rate of severe illness than the original COVID-19 strain, said Edward Desmond, the Health Department’s State Laboratories Division administrator, though he cautioned that there isn’t enough scientific evidence to support that conclusion.

“This is not unexpected,” said Desmond, noting that the Delta variant showed up in California about a month and a half ago.

Doctors have reported that as the Delta variant has spread in southeastern China, they’ve seen patients becoming sicker and their conditions worsening more quickly, The New York Times reported this weekend, with similar trends reported by doctors in Britain and Brazil.

So-called “variants of concern” now comprise the vast majority of coronavirus cases in Hawaii. They are flagged by health officials because they may be more contagious, make people sicker or may not be as responsive to the available vaccines.

Health officials are urging all Hawaii residents who are eligible, those 12 and up, to get vaccinated to stem the spread of COVID-19 and its variants. As of Monday 55% of Hawaii residents had been fully vaccinated, and 61% had received at least one dose of a vaccine, according to state data.

Overall, Hawaii’s case counts have remained low as more people get vaccinated, a promising sign as the state welcomes back visitors and restrictions on businesses and activities ease. State Department of Health officials reported 56 new confirmed and probable coronavirus infections Monday, bringing the state’s total since the start of the pandemic to 37,067 cases. The new confirmed and probable infection count by island includes 21 new cases on Oahu, 14 on Maui, four on Hawaii island, seven on Kauai and 10 Hawaii residents diagnosed outside the state.