- Two varieties of flu have not been seen for over a year, the STAT reported.
- Public health measures to control the coronavirus pandemic may have led to the disappearance of these strains.
- However, it is still possible that they circulate undetected.
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It has been a lonely year to be a flu virus.
Protection against infectious diseases introduced during the coronavirus pandemic to protect humans from COVID-19, such as mask requirements, school closures, and travel restrictions, made it virtually impossible for influenza viruses to travel as well as they normally do.
For example, the United States experienced a 98% drop in admissions due to influenza in the 2020-2021
This was not just a result of sick people being left out of the clinic during the pandemic.
“There was a lot of flu testing going on – there just wasn’t much flu virus,” Alicia Budd, a Centers for Disease Control and Prevention, told Insider during a recent association of Health Care Journalists scholarships. “The peak – if you can call it that – was 0.4% of the samples tested for influenza were positive.”
Usually during the high season for flu in the United States, the proportion of positive tests varies from 24% to 30%.
In fact, it is possible that the sharp drop in flu cases has been so dramatic this year that it killed some versions of the flu. Two varieties have not been seen for over a year, STAT reported. It could make it easier for vaccine manufacturers to build a better flu vaccine – one targeted at a declining number of threats.
But experts warn that it is still too early to draw any conclusions, partly because so few positive flu tests were recorded last season.
“The actual number of copies this year compared to previous seasons is extremely low,” Budd said.
“Of course, it’s still important to know what viruses are there,” she continued, adding, “It helps us understand a little bit what we may be looking for next season and if there are any updates to the vaccine.”
2 influenza viruses have been missing from databases for over a year
The influenza virus family is divided into two types: A and B. Type A consists of subtypes, two of which account for most type A influenza viruses in humans: H1N1 and H3N2. These are further divided into clays. Type B influenza, meanwhile, is divided into two genera, B / Victoria and B / Yamagata, which are also divided into clothes.
Since March 2020, there have been no reports of a specific hake of H3N2 (called 3c3.A) according to GISAID, a global database where researchers record and track which influenza viruses are circulating.
“I think we’re probably losing a little bit of H3N2 diversity,” said Richard Webby, a flu expert on St. Jude Children’s Research Hospital, to STAT.
He said it would be a “good thing” for the annual decision-making on which strains to target vaccines – a process Webby participates in each year.
“Right now when we sit down to make recommendations for vaccine strains, it’s always the headache virus,” he said of H3N2.
There have also been no reports of influenza virus in the B / Yamagata genus registered on GISAID since March 2020, but experts believe it is less likely to have disappeared.
“The Yamagata and Victoria lineage viruses have been in co-circulation for more than 30 years,” said Dr. Larisa Gubareva, an influenza virologist at the Center for Disease Control and Prevention, to Insider.
Although certain versions of influenza are declining in certain areas, she added, “they can still cause infections in areas with limited virological surveillance, or they can potentially adapt again to gain a competitive advantage.”
“Influenza viruses are constantly changing,” Gubareva said. “It is not uncommon to see new viruses or even groups of viruses emerge and then subside.”
This is also a difficult time to draw definitive conclusions about which influenza viruses are most prominent as so few people became ill last year.
In a normal year, influenza guards at the CDC collect and characterize thousands of influenza viruses and genetics, Budd said. “This season,” she said, “by the beginning of May we had just reached 10.”
Could this make it easier to create better flu shots?
If any flu strain is really gone for good, it would be good news for the researchers who produce annual flu vaccines.
The World Health Organization meets twice a year to predict which viruses will be dominant the following season so countries can produce vaccines on time. (The most recent meeting took place in February for the Northern Hemisphere.) But its predictions are somewhat hit-or-miss, as the flu continues to circulate and change in unpredictable ways at a rapid pace. If an influenza virus that is not well covered by the vaccine becomes more prominent than predicted, even vaccinated people may not be completely protected.
This was the case during the flu season 2017-2018, when three-quarters of the people who got the flu shot in the United States were not covered by the most common H3N2 strain that settled circulation. The CDC estimates that about 61,000 people died of influenza that season, the heaviest number of influenza in the United States since the 2009 swine flu pandemic.
Influenza monitors like Budd, however, are hopeful that this year’s shots might match circulating strains better. Out of the 10 flu viruses that the CDC discovered last season, four were H3N2s and four B / Victorias. These eight match all of the genetic groups covered by this year’s vaccine. It is still too early to predict what will happen to the flu in the fall and winter.
“We have to wait and see, because the flu is unpredictable,” Budd said. “However, I would certainly expect that as life returns more and more toward prepandemic ways, respiratory virus circulation is likely to return to something more what we are used to than what we saw last year.”