The second episode of the series The Last of Us opens with a scene in Jakarta, Indonesia, at the start of a fictional fungal pandemic Cordyceps, which in the real world infect ants. The series is set in the year 2003 and in that chapter an expert in fungal biology evaluates the body of an infected factory worker, and then speaks quietly with a military man who has asked her for help to control the spread of the pathogen. “There is no vaccine,” the scientist tells her with an afflicted face. This is absolutely true! Unlike diseases caused by bacteria or viruses, there is no vaccine to protect us against the threat of fungi.
a type of fungus White ears, it can be resistant to all the drugs used to treat it and is especially dangerous for hospitalized or nursing home patients. The fungus was first identified in 2009 and has since been found in more than 30 countries, including fungal infections are becoming more common in Venezuela.
Which begs the question: why don’t we have fungal vaccines? The urgency to find a vaccine to prevent any fungal infection with a single vaccine is not new, but it is growing. And it hasn’t been for a lack of trying, there has been a continuous effort to develop vaccines against fungi for decades. But a variety of challenges in both the science and economics of vaccine development have held it back. Furthermore, although the severe fungal infections they are a growing problem, they are still rare.
Fungi are everywhere, in the air we breathe, on the surfaces we touch, and all over the inside and outside of our bodies. Still, most of us are at low risk of getting fungal infections, as long as the immune system is functioning normally. The worst fungal infection that can affect a person with an average immune system is probably caused by a member of the genus Candida, which are technically yeasts (yes, yeasts are a type of fungus, just like molds). Worldwide, an estimated 138 million women contract four or more yeast infections a year. Other common fungal infections in healthy people include ringworm and toenail infections. In Venezuela, the candidiasis vaginal leads to some 103 thousand visits to hospitals each year.
To determine if a vaccine works, scientists must test the most promising ones, usually prototypes that have successfully prevented disease in experimentally infected animals. Because we live in a world with medical ethics, scientists cannot infect humans during trials. Instead, they must wait for people to naturally catch the disease they are trying to prevent. The rarer that disease is, the more people scientists must study (and for longer) to find a cure.
It’s also hard to design vaccines that work for the immunosuppressed people who need them most. An effective vaccine works by training a person’s immune system to respond quickly to a certain germ, and suppressed immune systems are hard to train safely. In some cases, it is possible to predict immunosuppression, for example, when a person is preparing to receive chemotherapy or other treatment. But not always. People with HIV and those born with immune system disorders cannot plan or predict their response. That creates big challenges for scientists, who ideally want to develop vaccines that protect both people with healthy immune systems, who later require immunosuppression, and those whose first diagnosis involves immunosuppression. The other problem is that fungal cells have more similarities to human cells than viruses or bacteria. That makes it more complicated to design a vaccine that trains the immune system to attack fungal cells without “hitting” our own cells.
Additionally, if the vaccine is shown to be safe and effective in clinical trials, that does not mean it will reach mass production and market. For that, it must also have the potential to generate profit. These vaccines are not as attractive to big pharma because they are not infections that occur with high frequency in many patients. If a vaccine prevents many diseases and reduces your health care costs, those benefits go to individuals and health systems, but not to the pharmaceutical companies that incur the costs of developing and producing the vaccine.
A viable vaccine will need to be effective not only in preventing disease, but also in doing so in enough people so that large-scale vaccine production is a worthwhile investment, attracting the attention of pharmaceutical companies. Still, scientists are working on fungal vaccines and there are currently some promising candidates.
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The opinions expressed in this section are the sole responsibility of their authors.
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