New Study Shows That Intravenous Injections Are More Potent And Effective Versus Conventional Intradermal Mode Of Delivering Tuberculosis Vaccine
Globally, more individuals die from tuberculosis
) than any other infectious disease, even though the vast majority were vaccinated
. The vaccine
just isn't that reliable. But a new Nature
study finds that simply changing the way the vaccine
is administered could dramatically boost its protective power.
Medical researchers at the University of Pittsburgh School of Medicine and the National Institute of Allergy and Infectious Diseases (NIAID) discovered that intravenous TB vaccination
is highly protective against the infection in monkeys, compared to the standard interdermal
injection directly into the skin, which offers minimal protection.
Senior author Dr JoAnne Flynn, Ph.D., Professor of Microbiology and Molecular Genetics at the Pitt Center for Vaccine
Research told Thailand Medical
News, "The effects are amazing. When we compared the lungs of animals given the vaccine intravenously
versus the standard route, we saw a 100,000-fold reduction in bacterial burden. Nine out of 10 animals showed no inflammation in their lungs."
Dr Flynn's team tested several routes and doses of the only commercially available human TB vaccin
e, Bacille Calmette-Guérin (BCG), which is made of a live, weakened form of TB
bacteria found in cattle.
The common BCG vaccine
has been around for 100 years and is among the most widely used vaccines in the world, but its efficacy varies widely.
The concept for an intravenous TB vaccination
came from earlier experiments by the other senior author on the study, Robert Seder, M.D., at the NIAID's Vaccine Research Center. Seder showed in both animals and humans that the malaria vaccine is more effective when delivered intravenously
To assess whether the method of administration matters for TB
, Flynn and colleagues separated their colony of monkeys into six groups: unvaccinated, standard human injection, stronger dose but same injection route, mist, injection plus mist, and finally, the stronger dose of BCG delivered as a single shot directly into the vein.
Half a year later, the researchers exposed the animals to TB
and monitored them for signs of infection.
Typically monkeys are extremely susceptible to TB
. All of the animals who received the standard human dose had persistent lung inflammation, and the average amount of TB
bacteria in their lungs was only slightly less than in the monkeys who received no vaccine
at all. The other injected and inhaled vaccines
offered similarly modest TB
The new approach of intravenous
vaccine, on the other
hand, offered nearly full protection. There was virtually no TB
bacteria in the lungs of these animals, and only one monkey in this group developed lung inflammation.
Dr Flynn explained, "The reason the intravenous
route is so effective is that the vaccine
travels quickly through the bloodstream to the lungs, the lymph nodes and the spleen, and it primes the T cells before it gets killed."
Dr Flynn's team found BCG and activated T cells in the lungs of all the intravenously vaccinated
animals. Among the other groups, BCG was undetectable in the lung tissue and T cell responses were relatively meagre.
The medical researchers next plan to test whether lower doses of intravenous
BCG could offer the same level of protection without the side effects, which mostly consist of temporary inflammation in the lungs.
Prior to this method being used on humans, researchers need to know that it's not only safe, but also practical. An intravenous vaccine
requires more skill to administer and carries a higher risk of infection
Dr Flynn further added, "We're a long way from realizing the translational potential of this work, but eventually we do hope to test in humans."
Reference : Patricia A. Darrah et al, Prevention of tuberculosis in macaques after intravenous BCG immunization, Nature (2020). DOI: 10.1038/s41586-019-1817-8