Health authorities are sounding the alarm after confirming two cases of measles and identifying at least 100 suspected cases in the east Fraser Valley.

The most recent exposure occurred in a school in Chilliwack in a community with traditionally low immunization rates, said Dr. Victoria Lee, spokeswoman for the Fraser Health Authority.

“We are seeing immunization rates overall declining, and that is dramatically affecting outbreaks.

“In the East Fraser region we have immunization rates of 60 to 70 per cent, but in some of the schools we are examining, the immunization rates are as low as zero per cent.”

Lee cited misconceptions about immunization safety, and philosophical and religious reasons for the decline.

The health authority’s warning about this outbreak extends to residents living in Abbotsford, Mission, Chilliwack, Agassiz, Harrison Hot Springs and Hope.

Public health staff are contacting affected families to offer immunoglobulin or vaccine to reduce the chance of the infection developing.

Lee said authorities will not be releasing the name of the school where the outbreak occurred until later this week.

Measles is a highly contagious and potentially fatal viral infection characterized by a rash, high fever, runny nose, coughing and tiny spots inside the mouth. The disease is airborne and is so contagious, said Lee, that you can get it by sitting next to an infected person who coughs or sneezes. The virus can live in the air up to two hours in unventilated areas such as bathrooms.

The disease can cause pneumonia, brain damage, deafness, serious complications among pregnant women and death. It is easily preventable through vaccination.

Because measles is so contagious, an overall immunization rate of at least 90 per cent is required to keep a population safe through “herd immunity,” which is higher than the average of 85 per cent required for other diseases, Lee said.

Although B.C. does not require children to be vaccinated before attending school, both Ontario and New Brunswick have compulsory vaccination laws for children enrolled in school.

Measles was considered eradicated as recently as 2011 in the United States, but clusters of outbreaks have become more frequent across North America.

In July 2013, the Public Health Agency of Canada issued a warning after measles appeared in B.C., Alberta, Ontario, Quebec, New Brunswick and Prince Edward Island. According to the Public Health Agency, most of those outbreaks were “travel-related.”

Lee said outbreaks are occurring more frequently all over the world, and no longer just in low-income countries.

In August 2013, Fraser Health confirmed two cases of measles in the Fraser Valley that were related to a large outbreak in the Netherlands, where more than 1,000 people were infected last year.

Lee couldn’t say whether the recent Chilliwack outbreak was related to travel, but did advise parents and families to visit a health professional to ensure their immunizations are up to date before travelling for spring break.

In 2011, there were 158,000 measles deaths worldwide.

Measles vaccinations are available free of charge to all B.C. residents born after 1957, Lee said.

dryan@vancouversun.com