“Hopefully we’ll have a vaccine ready for testing in two years. Yet another terrible disease is going to take a toll on patience, persistence, and sheer wisdom.”

United States Secretary of Health Margaret Heckler spoke about the HIV epidemic in 1984.

But four decades later and nearly 40 million people dead, the world still doesn’t have a vaccine against HIV.

Last week, Johnson & Johnson became the latest drug company to take on potential competitors.

The US company announced that the vaccine, the world’s only candidate, had failed late in a trial.

The study, known as MOZAICO, tested 3,900 men and transgender people in North America, South America and Europe. But while analysts concluded it was safe, the trial was halted because the vaccine was no more effective at preventing HIV infection than a placebo.

It’s another blow to an important field of research used to disappointment.

To date, eight candidate HIV vaccines have advanced to clinical trials. At the last hurdle they all failedOnly one trial in Thailand between 2003 and 2006 showed moderate efficacy.

Johnson & Johnson was trying to build on the modest success of the Thai study, but it ultimately didn’t work.

So why is it so difficult to develop a vaccine for HIV? After all, scientists caught the Japanese strain of Covid-19 and tested it within months of the virus’s arrival.

‘No one has HIV’

Experts are still confident that a successful HIV vaccine will one day be developed, but point to several formidable challenges that remain.

Perhaps most notably, there is no “road map in nature” for scientists to map or improve upon.

“When we get measles, we get rid of measles and there is an immune response that our body gets. [and we can design a vaccine] It reverses that response,” said Professor Salim Abdul Karim, director of the Center for AIDS Research in South Africa.

“Nobody is cured of HIV. There is no natural immune response. Nature has nothing for us to copy.

He added that when Sars-Cov-2 emerged, previous research into the first Sars outbreak had already identified what organ the coronavirus had to target – the so-called ‘spike protein’. But this is not the case with HIV.

“Even if we have the technology to make a vaccine, we don’t know what it is. [part of the virus] He should do it,” said Professor Karim.

“The HIV virus is also hidden in the chromosome CD4 cells, where it is not easily seen by the immune system,” said Tomas Hanke, professor of immunology at the University of Oxford, who has been working on HIV vaccines for 30 years.

He added that the genetic makeup of the pathogen changes rapidly – much faster than SARS-CoV-2, the Covid-19 virus. This means that by the time they develop a vaccine to fight it, the virus may already be active.

And finally, according to Professor Karim, there is no reliable animal model that can serve as a basis for HIV virus research.

“We have these real problems that make an HIV vaccine very difficult,” he said.

But optimism remains.

“[The latest setback] “It’s disappointing, but the positive thing is that we’ve learned,” said Professor Hanke. “[The Johnson and Johnson vaccine] It was designed several years ago, perhaps a time when we knew less. But the experiment found that some of the ways we use T cells and antibodies aren’t working, and we have a good idea of ​​how to improve them.

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