MEDFORD — Two new cases of pertussis, also known as whooping cough, have been reported in the Ashland School District and 15 “under-vaccinated” students exposed to the highly contagious respiratory disease are being held out of school for 21 days, Jackson County Medical Director Dr. Jim Shames announced Tuesday.

Sharing a podium with Ashland Director of Student Services Samuel Bogdanove in the Orchard Room of the Jackson County Health and Human Services building, Shames said the most recent outbreak comes on the heels of four previously reported Ashland cases, three of which came to light in mid-September.

Oregon law requires children who have not been vaccinated or are under-vaccinated who have had close contact with pertussis victims to be excluded from school for 21 days. Bogdanove said 27 students were excluded during the original outbreak and there is now a total of 42 students who have been kept out of school at some point over the last month, in addition to the six students with pertussis. “About half” of the original 27, he added, were later immunized and allowed back into school.

“It does seem that we have these clusters, these ongoing cases, and as you all know pertussis is a potentially serious illness,” Shames said. “It’s most serious when very young children, pregnant women, people who are immunocompromised, people who have cancer, the very old, the usual folks who can get very ill. So we are taking actions to both protect any vulnerable children in the schools and those particularly vulnerable populations.”

Citing confidentiality, Bogdanove declined to name the schools affected or the grade levels of the children who have been exposed.

Ashland, which also had a chickenpox outbreak in 2015, has earned a reputation as one of the state’s least-immunized student populations.

According to the Oregon Department of Education, the number of students in Ashland schools with all required vaccinations during the 2015-16 school year (the latest numbers available) ranged from just 50 percent at John Muir to 84 percent at Bellview Elementary, with four of the town’s six schools falling between 75 and 78 percent.

Those numbers pale in comparison to most districts. In Eagle Point during the same school year, for example, the lowest-vaccinated school was Lake Creek Learning Center at 82 percent, and seven of the town’s 10 schools had a 93 percent vaccination rate or higher. In Medford, 19 of the 23 schools had at least 92 percent of their student populations up to date on their immunizations.

Students entering school are required to be vaccinated from pertussis via a five-shot schedule followed by a booster shot at about age 11, but Oregon allows medical and religious exemptions.

“Well, we do have a relatively under-immunized population” Shames said. “And so it is to be expected that a vaccine-preventable illness like pertussis could spread from person to person within that educational community. So we know that, we try to prepare for that, we try and educate around that.”

The more children fully immunized, Shames added, the better chance a community has to avoid an outbreak which may eventually reach somebody who’s hyper-vulnerable.

“What we’re doing is trying to create a herd immunity,” Shames said, “a sense of protection that we all carry so that you don’t get sick and pass it to the next person, who eventually can pass it to somebody who is very vulnerable, like a newborn baby or a pregnant woman who’s about to give birth. That’s the basic principle.

“We have pertussis in our community. We would like folks to be diligent, pay attention. If you have a prolonged cough, perhaps go get it checked out, because the way you put a stop to a communicable disease is to identify it early, isolate people that are sick and get people who are sick treated so you can’t transmit the disease further.”

Joe Zavala is a reporter for the Ashland Daily Tidings. Reach him at 541-821-0829 or jzavala@dailytidings.com. Follow him on Twitter at @Joe_Zavala99.