While several vaccines have been developed against the coronavirus in record time, there is still no vaccine against HIV after 40 years. Why is it so complicated? What makes the virus so insidious?
A few months after the novel coronavirus SARS CoV-2 became known, there were already several very promising vaccine candidates. In the case of HIV, on the other hand, there is still no vaccine in sight, even though the pathogen was discovered around 40 years ago. Since then, the same question keeps popping up: Why is this so complicated? The simplified answer: because HIV is the chameleon among viruses and is able to change again and again.
Difficult to get a grip
One of the reasons why the HI virus is so difficult to combat is that it has a complicated, three-dimensional surface structure. Moreover, half of this surface is coated with sugar, scientists call it – glycolized. The immune system can attack such glycolized surfaces poorly. And a vaccine is also failing this sugar coating.
HIV is different
Vaccine research would presumably be several steps further along if the HI virus behaved like many other viruses. But that is not the case. It changes the shape of its viral envelope enormously rapidly from one generation to the next.
The AIDS virus is highly mutable
In order to be able to fight it, the immune system is dependent on recognizing the enemy. If the virus changes again and again, the immune system does not recognize it, does not consider it as a pathogen and does not attack it. This is how the HI virus constantly deceives the immune system and always seems to be one step ahead of research.
The HI virus belongs to the group of retroviruses. They have the ability to incorporate their genetic material into that of the host cell. Researchers have long sought to understand how retroviruses replicate in order to develop strategies for a cure. Again and again there are studies, again and again there are new disappointments, because the virus is apparently simply not under control.
One step forward, two steps back?
HVTN 702 was a large-scale vaccine trial that began in South Africa in 2016. 5407 HIV-negative individuals between the ages of 18 and 35 participated. In the study, a so-called "prime boost" was used-Scheme taken. Two vaccines are combined. The first vaccination – the "prime-Vaccination – has a different active ingredient than the later "Boost"-Vaccination. Behind this was the hope for a broader immune system response than would be the case with just one vaccine.
The HI virus triggers many different symptoms
The basis of the HVTN 702 trial is the RV 144 vaccine. It is the only one so far to show a protective effect – albeit quite small – of 31 percent in a study in Thailand. However, the protective effect lasted only a few months. 129 HIV infections had occurred among vaccinated subjects, 124 among those who had received a placebo.
However, in February 2020, the South African HVTN 702 trial was stopped as no clear success was seen.
The MOSAICO vaccine trial is another trial based on the prime-boost scheme. Again, the first vaccine, which goes by the term prime, consists of a different active ingredient than the boost vaccine. This vaccine contains a protein that replicates the complicated HIV surface. Trials with monkeys have already been run and have shown promising results. With the help of this vaccine combination, the probability of transmission of the HI virus could be reduced by almost 90 percent. Clinical trials have been underway in the USA since the end of last year. 3800 people are participating.
The third study worth mentioning is called IMBOKODO. It also falls into the category of prime-boost strategies with 2600 female subjects from various African countries. So far, the protective effect is a hopeful 67 percent. The trial began in November 2017 and is expected to run until February 2022.
Researchers worldwide are searching intensively for an HIV vaccine
The result counts
So the big breakthrough is still a long time coming. Researchers agree on one thing: even if one of the approaches to HIV vaccination is successful, we cannot expect 100 percent protection in the near future. But even a vaccination with a protective effect of 60 to 70 percent would be a success. Until then, the only option is to treat the disease with anti-retroviral drugs.
Prophylaxis as an alternative?
Precisely because research for a vaccine has been going on for so long without success, many hopes are resting on HIV prophylaxis with medication in the form of PrEP (also called HIV PrEP). The abbreviation stands for "pre-exposure prophylaxis", i.e. prevention of possible HIV contact. In the process, HIV-negative people take an HIV drug to protect themselves from HIV infection. The search is currently on for a way to administer these drugs as depot injections or implants over several months rather than daily in tablet form.
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