The specter of the 1918 pandemic, which killed tens of millions of people in a single year, haunts the world every time a new alert for flu from an animal arises. On that occasion, the fatalities were mostly young adults, but other times the disease preyed on children or the elderly . Why?
A joint study carried out by scientists from the universities of Arizona in Tucson and California seems to have found the answer: your year of birth, or more exactly, the form of microbe to which you have been exposed for the first time in your life marks indelibly. the ability to resist a certain infection in the future.
The experts analyzed two viral strains of type A, H5N1 and H7N9 (originating in birds), which have caused infections and even deaths in people. Both pathogens are susceptible to developing mutations that allow them to jump from animals to humans and then spread rapidly between the latter. What was interesting for the researchers was, furthermore, that the H5N1 strain usually infects young individuals, while H7N9 mostly affects older people .
The key is in a substance called hemagglutinin , the protein responsible for the union of the virus with the infected cell, of which there are 18 varieties for the influenza A pathogen. Only three (H1, H2 and H3) have circulated among humans in the last century, and, as North American researchers have discovered, they are responsible for the greater or lesser resistance against H5N1 or H7N9 .
Thus, those born before the 1960s, who have developed antibodies against the hemagglutinins H1 and H2, hardly suffer the worst effects of H5N1 , while people born after that decade, exposed to the H3 strain, are much better immunized against H7N9.
Michael Worobey, one of the authors of the study, believes that this explains the high mortality rate of the 1918 flu among young adults : “They died from an H1 virus, and from the blood analyzed many decades later it can be seen that these people had been exposed during their childhood to an H3. Therefore, they were not protected against that strain. The same could happen with the next pandemics. “
The new work points out that the protection rate against a compatible microbe is 75% against serious illness and 80% against death . A finding, say its authors, that will allow anticipating the possible ravages of pandemics by H5N1, H7N9 or other agents.
