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When vaccines don't work

In 1984, the US Secretary of Health and Human Services Margaret Heckler announced at a press conference in Washington, DC, that scientists had successfully identified the virus that later became known as HIV -- and predicted that a preventative vaccine would be ready for testing in two years.
Nearly four decades and 32 million deaths later, the world is still waiting for an HIV vaccine.
Instead of a breakthrough, Heckler's claim was followed by the loss of much of a generation of gay men and the painful shunning of their community in Western countries. For many years, a positive diagnosis was not only a death sentence; it ensured a person would spend their final months abandoned by their communities, while doctors debated in medical journals whether HIV patients were even worth saving.

The search didn't end in the 1980s. In 1997, President Bill Clinton challenged the US to come up with a vaccine within a decade. Fourteen years ago, scientists said we were still about 10 years away.
The difficulties in finding a vaccine began with the very nature of HIV/AIDS itself. "Influenza is able to change itself from one year to the next so the natural infection or immunization the previous year doesn't infect you the following year. HIV does that during a single infection," explains Paul Offit, a pediatrician and infectious disease specialist who co-invented the rotavirus vaccine.
"It continues to mutate in you, so it's like you're infected with a thousand different HIV strands," Offit tells CNN. "(And) while it is mutating, it's also crippling your immune system."
HIV poses very unique difficulties and Covid-19 does not possess its level of elusiveness, making experts generally more optimistic about finding a vaccine.

But there have been other diseases that have confounded both scientists and the human body. An effective vaccine for dengue fever, which infects as many as 400,000 people a year according to the WHO, has eluded doctors for decades. In 2017, a large-scale effort to find one was suspended after it was found to worsen the symptoms of the disease.
Similarly, it's been very difficult to develop vaccines for the common rhinoviruses and adenoviruses -- which, like coronaviruses, can cause cold symptoms. There's just one vaccine to prevent two strains of adenovirus, and it's not commercially available.
"You have high hopes, and then your hopes are dashed," says Nabarro, describing the slow and painful process of developing a vaccine. "We're dealing with biological systems, we're not dealing with mechanical systems. It really depends so much on how the body reacts."
Human trials are already underway at Oxford University in England for a coronavirus vaccine made from a chimpanzee virus, and in the US for a different vaccine, produced by Moderna.
However, it is the testing process -- not the development -- that holds up and often scuppers the production of vaccines, adds Hotez, who worked on a vaccine to protect against SARS. "The hard part is showing you can prove that it works and it's safe."

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Posted by Erin Burnett to The Global Outbreak at 3 May 2020 at 08:09

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