Why We Believe a Covid-19 Vaccine Will Be Found, When One for AIDS Has Not

RIO DE JANEIRO, BRAZIL – Will there be vaccines? This is certain. Will they be effective? We do not know that. For instance, a vaccine for HIV (the virus that causes AIDS) has also been developed, but it has never been successful. For SARS-Cov-2 (the virus that causes Covid-19) vaccines are currently being developed, and once they are tested we will be able to tell whether or not they work.

What we currently know is that no person infected with HIV has ever healed naturally through their immune system, but in the case of the novel coronavirus infection, many people have overcome the disease through the action of their own immune system, which is the very mechanism that vaccines use to fight viruses.

Why, from a scientific standpoint, should we believe that vaccines against SARS-Cov-2 will be effective when HIV vaccines have not worked? The underlying reason for scientists’ optimism is that this virus, unlike HIV, has a much, much lower mutation rate.

The virus causing AIDS changes so much that it is said that a person infected with it not under treatment has millions upon millions of different viruses, because each virus in that person’s body contains variations. This is not just one type of virus, but rather multiple, very similar viruses, with minor differences between them.

And a vaccine would be required to be effective against each one of these small variations, which also change over time. Since its mutation rate is so high, the fact is that a vaccine for millions and millions of different viruses would be needed.

With coronavirus, these variations are lower because its rate of error introduction when replicating is much lower. And since it’s a much more genetically stable virus, it is thought to be easier. That still does not mean it cannot change over time. This is something we do not know. But having said that, it seems that the coronavirus causing Covid-19 will never have the mutation rates of HIV, because they are different families of viruses with different replication mechanisms.

HIV produces many errors because it needs to transcribe itself: from RNA it becomes DNA to incorporate into the cell genome. Retrotranscription is essentially what causes so many mutations to occur in the case of HIV. On the other hand, retrotranscription is a step that is not present in the novel coronavirus, an RNA virus that does not incorporate itself into the cell genome.

The process that the coronavirus uses to replicate lacks this step and introduces far fewer errors. That is why a preventive vaccine against HIV has turned out to be one of science’s greatest challenges, but in the case of coronavirus, there is more optimism.

That it produces fewer errors than HIV when replicating does not mean that the coronavirus does not change, because it is changing, but these changes are slower and more predictable. By being able to predict how a virus is going to change, there are more chances to design vaccines and treatments that might be useful not only for the virus we are seeing now but also for those we believe may come in the future.

But optimism is not a certainty. Clearly, there will be vaccines, but we don’t know if they will be effective. When will we know? It will take months.

First, its effect on animal models must be proven. These pre-clinical data are required before moving on to clinical trials, i.e. testing them on humans. At best, assuming that research was started earlier this year, one must take into account that the minimum time needed to prove a vaccine’s efficacy and safety is at least two years.

And this is a record time because vaccines usually take five to ten years to reach the market and be employed. It is true that, in this case, one is talking about a year or eighteen months,  but it seems that before eighteen or even 24 months, this is virtually impossible.

In some cases, with vaccines that have been used before in pre-clinical models and are known to be safe, some steps are being skipped, but there is a stage that is the first and second, the stages in which safety and efficacy in humans are tested, which requires a study in a number of people over time to determine with certainty that they are safe. And there is no way to do that other than to allow that safety time to pass.

It can be reduced, but that entails risks. As a society we can accept such a risk, considering that we are in a very difficult situation and we probably will accept it, but these stages are designed to ensure that the treatments and vaccines reaching people are as safe as possible, and it is very important to respect that order and that pace, within which it is necessary to do everything possible to achieve a solution as soon as possible. But there are times that cannot be reduced, and to do so would not be a good idea.

Source: El País