With one of the highest vaccine-exemption rates in the country, Oregon is experiencing its largest measles outbreak in decades. This year’s count is now higher than anything seen since 2000, when the Centers for Disease Control and Prevention declared the highly contagious virus eliminated from the US.
Since the start of the year, Oregon has tallied 31 cases of measles, all in unvaccinated people. The cases have been accumulating in sustained waves of transmission since mid-June.
Vaccination decline
In 2000, when measles was declared officially eliminated, only about 1 percent of kindergarteners in the state had exemptions from childhood vaccines, such as measles.
Oregon’s exemption rate has risen since then, with the exemption rate now at 8.8 percent, according to the Oregon Health Authority. Any exemption rate above 5 percent is concerning. At that threshold, even if every non-exempt child is vaccinated, a state will not be able to achieve the target of 95 percent vaccine coverage expected to prevent sustained transmission of infectious diseases.
Health officials are directly linking the rise of non-medical exemptions to the current measles outbreak, which is centered in Clackamas, Marion, and Multnomah counties. All three are in the north-western corner of the state, with Clackamas and Multnomah in the Portland area.
Notorious virus
Measles is among the most infectious viruses known. It is notorious for its ability to stay aloft in indoor air for up to two hours after an infected person has been present. For unvaccinated people who are exposed, up to 9 out of 10 will end up falling ill. Those who become infected are contagious from about four days before developing the tell-tale rash and four days after it erupts. Other common symptoms of the infection include high fever, runny nose, cough, and conjunctivitis (pink eye). Many children become severely ill, requiring hospitalization.
In a small percentage of cases, measles can lead to severe complications, including pneumonia, encephalitis, and a progressive neurological disorder (subacute sclerosing panencephalitis), which develops five to 10 years after an initial infection. Additionally, measles is known to cause “immune amnesia.” That is, being infected with measles virus wipes out existing antibodies and immune responses to other germs, leaving people more vulnerable to other diseases.Two doses of MMR vaccine (measles, mumps, and rubella) are 97 percent effective against measles, and that protection is considered life-long.