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Pertussis outbreaks in Oregon partially linked to non-medical exemptions of students by their parents

PMG FILE PHOTO - Vaccinating children remains the most effective way of curbing an outbreak of pertussis or whooping cough.

An outbreak of the highly contagious bacterial disease pertussis, also known as whooping cough, has stricken 108 in students at 20 different schools in Lane County this year. Schools in Eugene and Springfield excluded students with non-medical and medical vaccine exemptions until the outbreak was over.

The disease hit close to home in Newberg as well. During a six-month period beginning in January, Yamhill County Public Health verified seven cases of pertussis at Newberg High School. It was considered an outbreak under Oregon Health Authority guidelines.

In a letter sent to parents, Yamhill County announced the potential for exposure to students at school from the first case on Jan. 2. Another notification letter was sent out by the school Feb. 11 announcing that a second case had been confirmed and that close contact exposure had occurred with members of the boys basketball and wrestling teams. That case also included a potential exposure period of three and a half weeks during January and subsequently, five more cases were confirmed by the end of February. 

An outbreak in Marion County in 2015 resulted in several dozen cases in two Salem high schools. Pertussis is most dangerous to infants, and caused five infant deaths between 2003 and 2015, according to the Oregon Health Authority.

A Pamplin Media Group reporter spoke to Dr. Karen Landers from the Marion County Health Department about pertussis and the link between outbreaks and vaccine rates.

PMG: What is the current rate of pertussis? How common are outbreaks?

Dr. Karen Landers: The numbers of pertussis cases have risen throughout the United States in recent years with very significant outbreaks. We typically see outbreaks occurring about every three to five years as new groups become susceptible to infection.

Pertussis is our least well controlled vaccine-preventable disease. This is due to a number of factors: It is most contagious and spreads before the beginning of the characteristic cough, and adolescents or adults may not have classic symptoms due to previous vaccination, as in chronic cough without whooping. It is not uncommon for adults to make multiple trips to a health care provider before the diagnosis of pertussis is considered.

The vaccine's protective effects, though highly effective right after vaccination, wear off over time, typically five years or so after the most recent vaccination, leaving people susceptible to infection if exposed. Even natural whooping cough disease does not confer lifelong protection. It may wear off some 10 to 20 years later.

The whole cell vaccine DTP, which was the first vaccine used, had a lot of side effects, so more recent vaccines have been using a purified form of antigens whose protection tends to wear off more quickly.

Until 2005, we had no vaccine booster for adolescents and adults, which created a situation where a susceptible population could both get and transmit the illness.

PMG: How important is vaccination in controlling pertussis?

Landers: Infants under 1 year of age and especially those who have not yet been vaccinated against pertussis have the highest risk of complications and death due to whooping cough. Our vaccination efforts focus on protecting them by vaccinating family members and others who may be close to them, such as child care providers, babysitters, health care providers. All pre-adolescents at age 11 to 12 years and any adults who haven't previously vaccinated should receive one dose of Tdap, the pertussis booster vaccine. To best protect vulnerable young infants, pregnant women should receive a dose of Tdap during every pregnancy, optimally at 27 to 36 weeks of pregnancy. This allows a mother's antibodies to be transferred to the newborn to provide protection until they receive their infant vaccinations starting at 2 months of age. There are already data showing this strategy prevents illness and complications in young infants and is safe for women receiving the vaccine each pregnancy.

PMG: What other vaccine-preventable diseases pose an increased risk due to declining vaccination rates?

Landers: Across the United States, there have been measles outbreaks linked to areas with low vaccination rates. Endemic measles was eliminated in the United States in 2000, meaning that there are no measles cases arising inside this country without an exposure of some kind outside the country; either someone enters the U.S. with the illness or an American citizen without immunity is exposed outside the U.S.

There was a very large outbreak of over 120 cases involving several states from December 2014 to the spring of 2015 associated with exposure from a visitor to Disneyland who brought the illness into the U.S. The vast majority of the outbreak cases occurred in California and were associated with under vaccination or no vaccination for measles. California has since passed legislation banning non-medical exemptions from vaccinations in order to attend public schools and saw a significant increase in kindergarten vaccination rates, the highest since 1998.

Oregon attempted to pass similar legislation, but it was vocally opposed and the legislation was changed to require all parents or guardians to participate in education on the effectiveness and safety of vaccinations prior to receiving a certificate permitting a non-medical exemption.

As part of that legislation, schools are required to make their vaccine exemption rates public to enable families with vulnerable children unable to be protected with vaccinations able to assess the risk.

Another vaccine-preventable disease that has seen recent increases is mumps. The increase in mumps cases is typically associated with outbreaks associated with colleges and other very close-knit groups of people. This has occurred across the country. Mumps cases often occur in persons who are fully vaccinated with two doses of the measles, mumps and rubella containing vaccine, MMR, and is believed to be associated with waning immunity.

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