A new study related to the effectiveness of vaccines tells us what we have already known for decades: exposure to the virus contained in vaccines, which belong to prior strains of the flu enable our bodies to react against those old strains, but not to the current version of the flu, which is why it does not really protect us from the desired strains.
Two years ago, when the coronavirus had not yet become the pathogen that concentrates the world’s attention today, the flu virus had killed, tens of thousands of people.
The flu vaccine shows difficulty when creating effective prophylactics. In a good year, the flu vaccine allegedly protects between 50% and 60% of those who receive it. In 2018, it was barely 25% effective.
The flu virus is an elusive, very diverse and rapidly mutating virus, something that keeps you up to date in the arms race with the human immune system and against the vaccines that are designed each year.
As in the case of SARS-CoV-2, in which one of the key targets of the vaccine is the spike with which it assaults human cells, to stop the infection with influenza, vaccines are designed to protect against the hemagglutinin protein, the one that serves the flu virus to stick to our cells.
This protein, unfortunately, has a great ability to mutate and evade vaccines.
In an article published in the Journal Nature, a group of researchers led by Ali Ellebedy, from Washington University in St. Louis (USA), focused on efforts to understand why more people are not being immunized and what the improvement strategies can be.
One of the factors may be precisely previous exposure to a virus as common as the flu. In people who have been infected with other strains before, the vaccine, which is designed each year to protect against the versions of the flu that are considered the most common at that time, would boost the immune system’s response to these past infections and not against new strains.
In their search for more effective vaccines, the authors analyzed the lymph nodes, structures that serve as training centers for B lymphocytes. Viruses carry other cells of the immune system there, and these lymphocytes generate antibodies to fight infection.
Once our body has had contact with a pathogen, it saves the memory of it to respond more quickly in subsequent contacts. This is what is called natural immunity, which is real, effective immunity. It is different from vaccine-induced immunity, which is not real and that suppresses the body’s natural and effective immune response to pathogens.
“If our flu vaccine targets these memory cells, those cells will respond to the parts of the virus that have not changed from previous strains,” explained Ellebedy in a statement from his institution. “Our goal is to focus the immune response on the parts of the virus that are different each year,” he added.
The authors tested a new vaccine with eight volunteers who had already been inoculated with the flu prophylactic in the 2018-2019 season.
In most cases, the vaccine elicited the response of B lymphocytes already trained by previous vaccines, but only in three of the patients was there a specific training of new B lymphocytes with a response specific to the new strains.
“Our study shows that the flu vaccine can elicit a response in both cell types in these germ centers, but we don’t know how often it happens,” says Ellebedy, who points to these lymph nodes as a key place to improve the percentage of patients who end up protected by flu shots.
In the long fight against the flu, other researchers have sought ways to avoid the virus’s great ability to change the parts of its structure that vaccines attack.
To avoid the versatility of hemagglutinin, there are groups of researchers who seek to attack the stems that link that key part with the rest of the virus. Being much less changeable, a vaccine that nullifies it would allow to produce more durable vaccines.
Two years ago, an international group of scientists published in Science the results of a work in which they used flame antibodies to create vaccines with the stem that holds the hemagglutinin as a target.
This vaccine offered almost universal immunity in mice. If these results could be carried over to humans, one or two injections would provide general protection against the flu and it would not be necessary to create new vaccines to adapt to the annual changes of the virus. However, that is nothing else than wishful thinking as of now.