The lineages that spread and cause most respiratory infections are A and B. As the World Health Organization notes, the latter, B/Yamagata, is no longer considered extinct.
Perhaps one of the good things this pandemic has left us with is that the arrival of SARS-CoV-2 led to the end of other viruses. Specifically, “it was the final nail in the coffin of the B/Yamagata influenza lineage,” said Raúl Ortiz de Lejarazu, honorary director of the National Influenza Center in Valladolid.
The World Health Organization has deemed this flu strain included in the flu vaccine, along with two A lineages and another B lineage, extinct in order to provide the broadest possible coverage of this respiratory virus. “On September 23, 2023, unprecedented measures were taken to WHO recommends no longer covering influenza B/Yamagata Influenza vaccines for next season in the Southern Hemisphere,” published in The Lancet Infectious Diseases.
It details the components of the quadrivalent vaccine to date: two influenza A viruses and two influenza viruses, B/Yamagata and B/Victoria. “However, B/Yamagata levels have declined significantly since the start of the COVID-19 pandemic, and such viruses have not been isolated or sequenced since March 2020,” the journal noted.
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Ortiz de Lejarazu points out that since 2018, two years before the arrival of the new coronavirus, “this lineage is no longer circulating.” What happened since 2020 is no longer observed, and its disappearance is not only due to the coronavirus The arrival of the virus and its measures are also due to other aspects of the virus and the response of our immune systems. ”
As virologist Adolfo García-Sastre, co-director of the Institute for Global Health at the Mount Sinai Center in New York, explains, “Not so long ago, when the first trivalent influenza vaccine was developed “There are only three serotypes of circulating influenza viruses” worldwide, human, influenza A H1N1, influenza A H3N2 and influenza B. For many years, vaccines were trivalent until it was discovered that influenza B had diverged into two antigenically distinct lineages, called Victoria and Yamagata, giving rise to the emergence of the quadrivalent vaccine.”
This situation lasted until 2020, when the Yamagata bloodline was no longer isolated, that is, it became rare or disappeared. García-Sastre elaborates: “At that time, the COVID-19 pandemic was upon us and the circulation of Yamagata bloodlines had been significantly reduced, and combined with the use of masks and the impact of the confinement, it was very likely that Make the mountain disappear completely.” “Therefore, there is no need to include this lineage in the flu vaccine. It would be difficult for it to reappear in the future, and if that happened, it could always be reincorporated into the annual vaccine.”
The honorary director of the National Influenza Center in Valladolid also mentioned the cross-protection of the two B lineages that have dominated so far. “The incidence of B/Victoria in B/Yamagata is higher than the incidence in B/Yamagata. This may also mean that people who receive the trivalent vaccine not considered in B/Yamagata will gain protection against both vaccines. This has Contributing to their disappearance is “due to a variety of factors that reduce their ability to reproduce and adapt”. Ortiz de Legarazu also remembers when the virus remains stable and its characteristics “do not change” , it is bound to disappear.
from lancet They also measured the consequences of removing B/Yamagata from seasonal vaccines. “Trivalent vaccines carry the risk of vaccine mismatch with circulating influenza B viruses, so some recommendations favor the use of quadrivalent vaccines for high-risk groups. However, these vaccines cost more and fewer doses are produced.”
Therefore, national recommendations may change to support the trivalent vaccine. The magazine insists that for manufacturers, “the question now is whether to focus only on the trivalent vaccine or update the quadrivalent vaccine to include another influenza A lineage other than B/Yamagata, which also Updated efficacy and potential clinical trials are needed to ensure the vaccine is effective.” Testing whether a quadrivalent vaccine is as effective as a trivalent vaccine. ”
In fact, “Influenza A lineage may induce broader immunity. In the meantime, further testing in B/Yamagata is needed to rule out the possibility of any resurgence,” the journal’s editorial explains. Once the season ends in the Northern Hemisphere, we will have to wait and see if the same decision is made for the Southern Hemisphere, as is usually the case.
In short, as the magazine concludes, the COVID-19 pandemic caused the disappearance of B/Yamagata. “This unintended consequence illustrates the power of non-pharmaceutical interventions (prevention measures such as wearing masks, distancing, isolation, etc.). Of course, it is necessary to balance possible adverse effects, but this result shows that status quo The absolute cycle of respiratory viruses is not inevitable.
The editorial cautions that while the strictest restrictions of 2020 are no longer needed, “simple measures like universal sick leave for anyone with respiratory symptoms could have an impact. In addition, this epidemiological change provides the opportunity for vaccination campaigns to and/or incorporate other lineages to provide broader coverage.
But this “is not a new era of influenza, but a return to a distant era when there were three antigenic variants of influenza,” Garcia-Sastre stressed.