When the vaccine arrives, will it already be “expired”?

Q: “As the virus reproduces with great success around the world, it must necessarily change somewhat by mutation over time. Could it be that an even more aggressive form appears? If so, would a vaccine discovered to fight the virus still be effective against this mutated form? ”Asks Pierre Hudon, of Knowlton.
A: Indeed, all viruses “mutate”, that is to say that from one generation to another, their genetic material changes little by little, which will modify the proteins on their surface. Since the antibodies that our immune system “learns” to make target these proteins, they become ineffective if the virus mutates too much.

In this little game, some viruses are faster than others: a study published in 2010 in the Journal of Virology found mutation rates varying by a factor of 10,000 from one type of virus to another . But it’s not just the mutation rate that counts: the proteins of some viruses easily become “dysfunctional” with the slightest mutation, while other viruses are more “tolerant” to mutations. Smallpox, for example, mutates about twice as fast as influenza , but it is much less tolerant of these mutations, which make it unable to infect cells. The bottom line is therefore always the same “version” of smallpox that lasts, and that is why the smallpox vaccine remains effective for tall life unlike that against the flu, which must be renewed annually.

As far as the COVID-19 virus is concerned, what we know for the moment is that it is a “RNA virus” (RNA is a form of genetic material less stable than DNA), says Dr. Guy Boivin, of the Research Chair in Emerging Viruses at Laval University, which means that he mutates quickly. Which is obviously not good news.

But on the other hand, adds his colleague from UQAC, the virologist Tarek Bouhali, “certain cells, like those of humans, are provided with a kind of” revision system “which makes corrections when errors are made when copying genetic material [note: this prevents mutations to a certain extent]. And the COVID-19 virus also has this capacity. That’s why we think it doesn’t change much. It remains only a hypothesis for the moment because this virus, we are still discovering it. But so far, we haven’t found any big differences between the strains of the virus in China and those circulating elsewhere in the world. ”

This is rather encouraging. It is unclear, however, whether COVID-19 is a virus whose proteins can remain functional despite a certain degree of mutation, says Bouhali. “We are learning,” he sums up.

In addition, he adds, there is another unknown in all of this. “Right now, we are almost all” naive “against this virus [note: very few people have immunity]. But as people get infected and have antibodies, they will develop immunity, and a possible vaccine will have the same kind of effect. From the moment there is population immunity, perhaps there will be a natural selection that will be exerted on the virus. ”

This is what, says Mr. Bouhali, can make the virus evolve. COVID-19 can currently infect us easily since very few people are immune. It therefore has less need to have particular characteristics to reproduce, which means that the selection pressure is low. But a more intense selection could eventually change it.

It remains to be seen if this will happen – and if so, how it will change.


COVID-19 raises a lot of questions. In order to respond to as many people as possible, science journalists have decided to join forces. The media members of the National Cooperative of Independent Information ( Le Soleil, Le Droit, La Tribune, Le Nouvelliste, Le Quotidien and La Voix de l’Est ), Québec Science and the Center Déclic team up to answer your questions . You have some? Write to us . This project is made possible thanks to a contribution from the Chief Scientist of Quebec , who invites you to follow him on Facebook , Twitter and Instagram .

Previous Article
Next Article

Leave a Reply

Your email address will not be published. Required fields are marked *