Vaccine shortage threatens yellow fever response

 Limited supplies of the yellow fever vaccine is stalling full response efforts to the yellow fever outbreak in parts of Africa It takes six months to develop the vaccine. Confronted by acute shortage of vaccines to protect millions potentially at risk of yellow fever, public health officials are struggling to manage the disease outbreak in Angola and the Democratic Republic of Congo, even as worries that the virus could spread are making the rounds.
 The prevailing yellow fever transmission has been explosive and has rapidly exhausted global emergency stockpile of at least six million vaccine doses.
It is feared that a second outbreak in a densely populated country could deplete the dangerously low vaccine supply. Currently, experts are anxiously watching the progress of the outbreak and are concerned it could spread to countries that have never faced large scale outbreaks of the virus before and therefore have little natural immunity.
 As a stop-gap measure aimed at providing at least some protection, the World Health Organization (WHO), is vaccinating14 million people against the disease in 8,000 locations by diluting the vaccine to one-fifth the dose.
 Millions have already been vaccinated with a full dose of the protective yellow fever vaccine that provides lifelong protection, but as supplies have dwindled, health officials are implementing the emergency measure that involves diluting the vaccine further so that it will provide protection for one year.
 Health experts say the current vaccination plan may be inadequate to protect enough people, hence they have warned that the virus could spread and possibly reach densely populated regions in Africa and Asia, where the disease could rapidly become endemic.
 "Protecting as many people as possible is at the heart of this strategy. With a limited supply we need to use these vaccines very carefully," said William Perea, Coordinator for the Control of Epidemic Diseases Unit at WHO said in a statement.
 Yellow fever "transmission in 2016 has been explosive and rapidly exhausted the usual global emergency stockpile of at least six million vaccine doses. But a second outbreak in a densely populated country could deplete the dangerously low vaccine supply.
 Since December 2015, the yellow fever outbreak has infected over 5,000 persons with over 400 deaths in Angola and the Democratic Republic of Congo. The disease is spread by mosquitoes, especially the Aedes aegypti mosquito that also spreads Zika virus.
 Symptoms of yellow fever include fever, chills, severe headache, back pain and nausea; the virus has been fatal in approximately 20 percent of cases. Health officials are fighting the virus on two fronts, by treating people and reducing mosquito populations so it doesn't spread across the continent or globe.
Researchers from the Centers for Diseases Control and Prevention said: "This epidemic in the three countries and its introduction to seven other countries illustrates how all countries are connected and that a threat in one country is a threat everywhere."
 It is believed that Yellow fever is "tenacious" and the number of cases in Africa is probably far higher than what had been reported.
 About 99 per cent of people develop immunity within one month of vaccination with the Yellow fever vaccine, which is a live-virus vaccine that has been used for several decades. A single dose provides lifelong protection for most people.

New layers of immunity found in TB/HIV co-infections

Researchers at the Tulane University have discovered that some monkeys whose immune systems are depleted by the Simian strain of HIV have a second line of defense against tuberculosis. 

The research led by Deepak Kaushal, a Professor of Microbiology and Immunology at the Tulane National Primate Research Center,  said it could have significant impacts on future vaccines for TB. 

People co-infected with Mycobacterium tuberculosis (Mtb) and HIV are up to 20 times more likely than people without HIV to develop active, clinical tuberculosis over their lifetimes. 

HIV targets CD4 T cells and researchers believe depletion of those cells, the first layer of immune response, drives up the progression of TB. Currently, most vaccines being developed for TB only target the CD4 arm of immunity.

Kaushal's research team exposed macaques to Mtb and simian immunodeficiency virus (SIV) to replicate human co-infection. They discovered one-third of the animals maintained latent TB despite complete loss of lung CD4 T cells. 

A study of the lung tissue revealed CD8 cells and B cells both worked to provide immunity against active TB.

Kaushal says future vaccines for tuberculosis should try to elicit immune responses from not only CD4 cells but also CD8 and B cells.

"This monkey model is the closest we can get to the human environment of these two diseases," Kaushal says. "This discovery is important because it lays out the whole gambit of the different immune functions that are required for an optimum response."

The research revealed a sub-population of macaques better able to fight TB and HIV co-infection, and Kaushal says it can be presumed this sub-population of humans also exists. He believes the difference is genetic.

Kaushal hopes to continue the research and move on to the next step of developing a vaccine. "Our job now is to find out the mechanism of why these differences occurred," Kaushal says.

The findings are published in the Proceedings of the National Academy of Sciences,