State Laboratories Division Administrator Dr. Edward Desmond on Monday discusses the first case of the Delta variant of COVID-19 found in an Oahu resident who visited the Mainland. The variant was first discovered in India, where COVID-19 sparked a public health crisis in April and May. The Maui News / COLLEEN UECHI photo

An Oahu resident who was vaccinated and traveled to Nevada has contracted the first known case of the Delta variant of COVID-19 in Hawaii, though state health officials credited the vaccine with stopping further spread among the person’s contacts.

The B.1.617.2 strain was first detected in India in February, shortly before the virus sparked a public health crisis in April and May. The Delta variant has become the dominant strain in the U.K. and currently makes up about 6 percent of all cases in the U.S., according to the state Department of Health.

“Early evidence suggests the Delta variant might spread more quickly than other SARS-CoV-2 strains,” State Laboratories Division Administrator Edward Desmond said in a news release Monday. “There are reports the Delta variant produces a higher rate of severe illness than original COVID-19, but we do not yet have enough evidence to support that conclusion.”

The Oahu resident had been fully vaccinated for COVID-19 before traveling to Nevada in early May, when the Delta variant was first reported in that state. The person tested negative prior to leaving Nevada but developed mild symptoms consistent with COVID-19 several days after returning to Hawaii and tested positive for the virus. The person was isolated, while household and close contacts were quarantined.

“It doesn’t appear that any further transmission has resulted from this case,” acting state epidemiologist Dr. Sarah Kemble said during a news conference on Monday afternoon. “However, one of the things that’s of some concern was that the person was fully vaccinated, had two doses of mRNA vaccine. So it is a vaccine breakthrough case, and we do see those from time to time, and we’ve seen those with other variants as well. I do think many of the other household contacts being vaccinated also played a role in this not transmitting further.”

Kemble said she wasn’t sure what vaccines the resident’s contacts had gotten (Pfizer and Moderna produce mRNA vaccines, while the Johnson & Johnson shot relies on DNA) but said many had been fully vaccinated. While the vaccines are not 100 percent effective, those who are fully vaccinated and contract the virus have a lower viral burden, reducing the chance of them spreading the disease. If their contacts are also vaccinated and exposed to this lower viral burden, their chances of getting infected are “even lower.”

“It’s that Swiss cheese model. You’re having those layers that are preventing the virus from taking the next step and jumping to the next person or being further transmitted,” Kemble said. “That’s part of the concept of herd immunity.”

The chance of getting the virus after vaccination remains low; Kemble said that there have been 170 breakthrough cases in Hawaii since vaccination efforts began in December, making up less than 2 percent of the cases in the state from month to month. She said that the breakthrough cases have included the B.1.1.7 variant first found in the U.K., and the B.1.429 variant first found in California, which “mirrors the breakdown of variants in the state overall.”

The B.1.1.7 variant remains the dominant strain statewide, but numbers vary by county, Desmond said, pointing out that the B.1.429 variant is more common on Maui and Hawaii island.

The State Laboratories Division did genome sequencing to identify the Delta variant in Hawaii, Desmond said. The division has been genome sequencing since June 2020, examining 50 to 100 specimens a week, and has developed a testing algorithm designed to find variants in a timely manner, according to the Health Department.

Kemble said there is no conclusive data showing the Delta strain causes more hospitalizations, as the B.1.1.7 variant has. However, the fact that it has spread quickly among several different geographic reasons does create concerns that it’s more transmissible than other strains.

“There was some concern initially by looking at studies in the test tube that antibodies have a harder time neutralizing this strain of the virus as has been found with some of the other variants of concern,” she said. “However, in real world studies when . . . you actually look at people who’ve been fully vaccinated and compare them with people who are not who have this strain, it does look like the vaccines that are out there now are still quite effective against this strain.”

As of Monday, 53 percent of Kauai County’s total population had been fully vaccinated, followed by 48 percent in Honolulu County, 47 percent in Hawaii County and 46 percent in Maui County, according to the Department of Health. (County-by-county breakdowns do not include federal doses.) Statewide, 55 percent of the total population has completed vaccination, which includes federal doses.

Starting today, the state is lifting restrictions on intercounty travel, which Kemble said makes sense given that more than half of the local population is vaccinated.

“Travel to and from the Mainland is of a little more concern, because there are some pockets in the United States where vaccine rates are much lower, and so we do see continued importation of variants from some of those states,” she said.

* Colleen Uechi can be reached at cuechi@mauinews.com.