Medical News
TB vaccination could be
made more effective
BCG vaccine gives macaques more protection after being injected
directly into their veins rather than under the skin
D
eveloped over a century ago, the world’s only
licensed vaccine to combat tuberculosis may be
on its way to getting a new boost.
The Bacille Calmette-Guerin vaccine, known as the
BCG jab, is given to infants through a needle placed
just under the skin. It protects babies from a form of
the disease called disseminated TB but is far less
effective at preventing pulmonary TB, a major cause of
illness and deaths in teens and adults.
Researchers at the National Institute of Allergy
and Infectious Diseases in Maryland and other
institutions have shown that simply changing the route
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MARCH 2020
of administration, i.e., into the vein, greatly increased
the vaccine’s ability to protect rhesus macaques
from infection after being exposed to Mycobacterium
tuberculosis, which causes TB.
The findings provide a new understanding of
how BCG protects against tuberculosis, while also
supporting further investigation of intravenous BCG
administration through clinical trials to determine
whether this route improves its effectiveness.
To control infection and prevent clinical disease,
a TB vaccine must elicit strong, sustained responses
from the immune system’s T cells, specifically those
in the lungs. However, the current intradermal route of
BCG administration, i.e., just under the skin, may not
generate enough of these critical cells in the lungs.
The researchers suspected that taking the
intravenous or aerosol route would overcome this
hurdle and give substantially better protection from
infection in rhesus macaques after they had been
dosed with the TB bacterium.
In their study, the scientists assessed the
primates’ immune responses over 24 weeks following
vaccination. They found the intravenous route resulted
in the highest durable levels of T cells in the blood and
lungs.
Six months after vaccination, the researchers
exposed the vaccinated macaques to a virulent strain
of the bacteria directly into their lungs and tracked
disease development over three months. Ninety
percent of the animals vaccinated intravenously were
highly protected. Just a few showed no detectable
infection or very low counts of the TB bacteria in lung
tissue.
The investigators concluded that intravenous BCG
“represents a major step forward in the field of TB
vaccine research.”
Assessing the study, Dr Chris Lowbridge, a
tuberculosis and infectious diseases expert at the
Menzies School of Health Research in Darwin, said
alternative vaccination routes had been considered
previously, but what stands out from this research
is how intravenous administration seems to protect
against both the development of the TB virus and
infection.
“Potentially, it could have a big impact, but it’s
important to note some limitations,” Dr Lowbridge,
who was not involved in the study, told Global Health
Asia-Pacific.
“First, it was done in macaque monkeys, so a lot
of further work will be needed before starting to look
at clinical testing of intravenous administration. An
intravenous vaccine is also harder to administer than
an intradermal one.”
This would be an issue in developing countries,
which tend to have the highest burden of TB.
“There would be a lot of work needed to train health
staff and provide additional resources to support this
alternative route of administration,” he added.
GlobalHealthAndTravel.com