In these days when the numbers of those affected by COVID-19 continue to grow, a recurring issue we all ask ourselves is: how long will it take for the vaccine to end the coronavirus pandemic? A question that can be extended to other infectious diseases such as Ebola, malaria, or AIDS, against which it has been fighting for much longer and yet they still do not have an effective vaccine. In this article, we analyze the coronavirus vaccine methodology and answer the question, why is there still no vaccine for coronavirus?
The development of a vaccine is a complex process. To begin, it is necessary to start with prior knowledge about the biological and immunological characteristics of the pathogen -virus, bacteria, or parasite. Next, the vaccine candidate would have to be synthesized and tests carried out to evaluate its efficacy. Finally, if the previous steps have been successful, all legal requirements must be met when they are put into circulation.
In a way, the process can be compared to a war against the pathogen that requires a careful strategy to achieve final victory.
CORONAVIRUS VACCINE: KNOW THE ENEMY
Throughout evolution, pathogens have developed multiple weapons and strategies to evade the host’s immune response. Sometimes they have proteins that allow them to suppress the immune system, or to trick it into causing our body to develop ineffective responses. Other times, their strategy is based on a constant mutation capacity that allows them to escape again and again from our defences, as it happens with the influenza virus.
A detailed knowledge of the biology of the pathogen, the structure of its proteins and the clinical characteristics of the associated disease decisively influence the success of the vaccine. In cases such as the one in question, in which the adversary we are dealing with is new, previous studies on similar microorganisms may be essential.
CHOOSE WHERE TO AIM
The choice of the antigen or antigens – that is, the pathogen proteins that are included in the vaccine – is an essential aspect in the design of the attack strategy.
In the 18th century, Edward Jenner laid the foundations for vaccination using an entire microorganism as an immunogen, giving rise to one of the great milestones of medicine, the eradication of smallpox. But this strategy is neither possible nor safe for all infectious diseases, and today there are different types of vaccines.
So-called “subunit vaccines” are currently being imposed, in which an antigen of the pathogen is chosen against which to direct the response. This choice is not easy, since it is a basically empirical process: although there are some tools to predict the immunogenicity of a molecule, and knowing the pathogen well is helpful, you always have to prove what works and what doesn’t.
An added complication is that, normally, the vaccine recipe also includes adjuvants-compounds that promote the induction of a stronger response to the antigen. Choosing the right combination of antigen and adjuvant requires testing. And this implies time, something very valuable in situations like the current one.
EVALUATE THE STRATEGY
Once the attack strategy is chosen, it is necessary to check if it is effective. To do this, it must first be tested on animals. On the one hand, the induction of the immune response is evaluated after pricking the vaccine prototype in the experimental animal, studying the type of immune response that is induced, and its ability to neutralize the enemy microorganism.
To assess the results, you should have prior knowledge that correlates the immunological parameters measured in the laboratory with the degree of protection conferred on the patient. This implies having data obtained from patients who have overcome the disease. And again, this takes time.
Another possibility is to have animal models that develop the disease to puncture the coronavirus vaccine and assess protection against subsequent inoculation of the pathogen. These animal models of disease are extremely useful, but their development requires effort and, of course, more time.
SMALL BATTLES FIRST, THEN WAR
Once animal testing has been passed, the time comes to assess human safety and efficacy, i-e clinical trials. The safety of the vaccine candidate is first assessed in a small group of healthy volunteers – phase I trials -, and then they move on to larger groups in which to test the appropriate doses and guidelines – phase II.
If all goes well, the efficacy of the vaccine is evaluated in an even greater number of individuals –phase III–. After this process, the vaccine can begin to be produced. And it must be done in adequate quantities and ensuring the high standards of quality and legality required by the pharmaceutical industry. Each step must have the approval of the competent authorities to guarantee the safety of all.
In emergency situations like today, these tests can be accelerated, of course. But surely not as much as we would like, since we must not forget that they constitute a chain: if we skip one step we are more likely to fail in the next.
Although the saying goes that Zamora was not won in an hour, in the end, it was won. The same happens with the development of coronavirus vaccines: although in situations like the current one the apparent slowness of the process can be frustrating, with time and effort it is possible.