(Adds reporting credit)
Nov 1 A face-to-face educational method used
among Orthodox Jews apparently led to a U.S. outbreak of mumps
in 2009 and 2010 even though most of those infected had been
properly vaccinated, according to a U.S. study.
The outbreak, detailed in the New England Journal of
Medicine, indicates how close, repeated contact with an infected
person can overwhelm the mumps vaccine, the researchers said.
"The risk of infection with mumps may be higher when the
exposure dose of virus is large or intensely transmitted," wrote
lead author Albert Barskey, of the U.S. Centers for Disease
Control and Prevention's (CDC) National Center for Immunization
and Respirators Diseases, and colleagues.
This may also explain why the mumps vaccine tends to be less
effective among household contacts than among school or
community contacts, they added.
In the mumps outbreak, 3,502 cases were reported over a
one-year period beginning in June 2009 in New Jersey, New York
City and New York State's Orange and Rockland counties. A camp
in the Catskill Mountains was the source.
The researchers, from the involved state health departments
and the CDC, studied 1,648 of those cases, nearly all of them
Orthodox Jews. The researchers found that 89 percent had
received the recommended two doses of mumps vaccine.
Many attended a religious school known as a yeshiva, where
boys receive intense training with a study partner known as a
chavrusa, who sits across a narrow table. The teaching method
often involves animated discussions and the partners are
switched several times a day.
The researchers wrote that "chavrusa study, with its
prolonged, face-to-face contact," probably resulted in high
exposures to the virus, and these "overcame vaccine-induced
protection in individual students."
The large families in Orthodox Jewish communities also
contributed to the spread, Barskey told Reuters Health in a
"As the outbreak went on, we started to see younger and
older cases, and females as well. What that suggests is there
was spread in the households. From family it would jump to a new
school," he said.
"The chavrusas played the biggest role. The households
played a lesser role."
The source of the outbreak was eventually traced to an
11-year-old boy, who had himself received two vaccine doses but
nonetheless picked up the disease in the United Kingdom, where
fears about vaccination had led to a large mumps outbreak.
That child attended the camp, which had about 400 Orthodox
(Reporting from New York by Gene Emery at Reuters Health;
editing by Elaine Lies)