I.N SEPTEMBER 2020 doctors and health officials in the northern hemisphere were on alert. They did not know how Covid-19 would behave in the first winter of the pandemic. Respiratory viruses tend to grow in cold weather. And there have been common concerns about the flu, a virus that changes shape, that gets sick and kills a lot of people every year. At worst, doctors feared they would see simultaneous outbreaks of Covid-19 and flu, which would overwhelm hospitals and lead to an increase in deaths – “twindemia”.
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This never happened. In late 2020 and early 2021, Covid-19 cases continued to rise in much of the world, but the flu wave never occurred. And yet today the same experts are concerned again. The lack of flu in 2020-21 is likely to have worsened the outlook for 2021-2022: outbreaks could occur earlier, last longer and affect far more people than usual.
Seasonal flu is caused by a group of viruses circulating around the world among birds, humans and other mammals and between them. The flu season in the northern hemisphere, which for this purpose is conventionally defined as North America, Europe, North Africa and West Asia, usually begins around October each year and peaks in January or February next year. In the southern hemisphere, the season begins around May and peaks from June to August.
Two types of the virus cause winter flu. Influenza A viruses occur in birds and pigs. The X1N1 and X3N2 subtypes (named after the structures of the two proteins on their surface) also infect humans. Influenza B infects only humans.
When these viruses mutate and spread, they are able to reconfigure the proteins that sit on their surface, making them less recognizable to the human immune system, even those who have previously encountered similar viruses. As a result, influenza vaccines need to be updated and re-administered every year.
Manufacturers need at least six months to create, test and produce a large number of influenza vaccines, so they must decide long before the flu season which versions of which vaccines should be targeted. It is at this point that the World Health Organization (World Health Organization) gives way.
Global Influenza Surveillance and Response System (GISRD) is a network of laboratories and health facilities in 123 countries that collect airway samples throughout the year. They sequence the genes of any influenza virus and characterize the proteins on their surface to build a detailed picture of the most common influenza viruses in circulation as these viruses develop and which new ones emerge.
Armed with this data, every February and September World Health Organization brings together experts to recommend which influenza strains should be targeted by future vaccines for the northern and southern hemispheres, respectively.
In February 2021, these experts, using information on viruses circulating in previous months in the southern hemisphere, selected four viruses for this year’s vaccines for the northern hemisphere. By early October, these vaccines should be in service.
The first big uncertainty for the coming winter is whether they picked the right viruses. This is always a problem, but especially acute this year. Much less information was available from GISRD because the 2020-2021 flu season was not such an event around the world (see chart). Less than 0.2% of samples worldwide tested positive for influenza between September 2020 and January 2021, according to World Health Organization. In the period from 2017 to 2020, the rate was 17%. The number of flu hospitalizations in America in the 2020-21 season was the lowest since such records began in 2005. The Centers for Disease Control and Prevention said it had received one report of a child dying from the flu in the 2020-21 season in America, compared to 199 in 2019-20.
What explains such a low level of influenza? Because of COVID-19, people wore masks, social distance, washed their hands, avoided public transportation and stayed home. It has also helped limit the spread of other respiratory viruses, including influenza.
This happy outcome has an alarming outcome. Influenza vaccines are generally less effective than Covid-19 vaccines; they prevent about 70% of detectable infections in healthy adults and about 50% in the elderly. How well a vaccine works depends on how well its components match the viral strains that a person actually encounters. If they are poorly matched, vaccines are less effective in preventing both infections and serious diseases, leading to worse epidemics. Given the lack of information on which influenza strains are circulating, the Academy of Medical Sciences (AMS) in Britain believe that the probability of discrepancies this year is higher.
The second big uncertainty is how the immune system of people who have mostly avoided the flu for more than a year will react when they face it. The easy or non-existent flu season 2020-21 could probably have been welcomed at a time when Covid-19 was killing tens of thousands of people and sending many more to the hospital. But it also means that far fewer people have been exposed to circulating flu viruses in the past year, so the level of innate immunity in the population will be relatively low. The flu wave in such conditions “could be problematic,” he warned AMS.
Even those who have been previously exposed are at risk. Immunity decreases over time. Worse, flu viruses change quickly, so the immune system’s memory of one season’s flu may have limited benefits against new viruses. Some of them are virtually immune to the flu – infants and young children who have never been exposed to it.
Research on previous flu outbreaks in America gives some clues as to what might happen in 2021. A 2013 study examined what happened after a mild winter, when influenza transmission rates tended to be lower than usual, and thus led to epidemics of lower intensity. The researchers found that 72% of subsequent epidemics were more severe than average. They started 11 days earlier and the epidemic growth rate was 40% higher. Their severity probably worsened their earlier onset because fewer people would have been vaccinated at this point.
Simulation by AMS showed that if Britons return to their pandemic lifestyle, the country could at worst face a winter flu epidemic 2.2 times more deadly than usual. In recent years, the flu has typically killed 10,000 to 30,000 people annually in England. The 2017-18 season was the latest bad season with about 26,000 deaths.
Respiratory syncytial virus (RSV) gives more clues as to what the northern hemisphere can expect. RSV is a major cause of hospitalization and death of young children, especially those under one year of age. Reports from around the world showed a 98% reduction RSV during a pandemic. But researchers from Australia have also found that after restrictions on physical distance have been eased in the last few months of 2021, RSV cases arose. They peaked in December (summer in the country) and not in the usual June or July (its autumn / winter). The peak itself was almost three times higher than usual, and the incidence of infection in older children was much higher. Doctors in New York found similar results after March 2021.
In the grip of winter
If the flu or RSV When COVID-19 levels are high, some doctors worry that people may be infected with multiple respiratory viruses at once. About one-fifth of children who are hospitalized with severe lung disease are infected with multiple viruses, says Stephen Holgate, a pharmacologist at the University of Southampton. Increasing evidence suggests that influenza and SARS–SFr.In-2 can coexist and they interact negatively, he explains. The AMS believes that influenza A infection makes people more susceptible SARS–SFr.In-2. He also worries that the wider spread of other respiratory viruses could lead to more dangerous options SARS–SFr.In-2.
Three steps will need to be taken to prevent the Twindemia in 2021-22, says Anne Johnson, an epidemiologist at University College London and president AMS.
First, a concerted effort to get more vaccines – both against Covid-19 and against the flu – is in place. Since natural immunity to influenza is probably the lowest in many years worldwide, immunity through vaccines will have to make up for the shortfall. This will mean striking at those who are usually at high risk, such as the elderly, pregnant women and healthcare professionals, as well as children, who are huge spreaders of the infection.
Second, because the symptoms of various respiratory diseases, including Covid-19, are similar, physicians and clinicians need regular access to multiplex testing in which throat swabs are tested for different viruses simultaneously. Express flu tests should be available in hospitals, clinics, nursing homes and pharmacies, says Professor Johnson. Detecting infections is helpful – timely use of antivirals can reduce the flu episode.
The third way to fight off the beetle is for ordinary people to practice what Professor Johnson calls “respiratory hygiene”. The rules of social distancing may no longer apply in much of the world, but people still have to wear masks in crowded rooms. They should also work from home where possible and communicate outdoors, she says.
Scientists will meet the upcoming flu season using tools they know work. But the current process of producing flu vaccines is slow – it takes six months and involves incubating the viruses in chicken eggs or mammalian cells before carefully isolating and purifying the proteins that then make up the building blocks of vaccines.
Messenger success RNA (mRNA) Covid-19 vaccines have prompted scientists to explore how to use the same flu technology. mRNA should speed up the process, leaving less time between vaccine preparation and virus mutation. And mRNA with the advent of new strains the vaccine is easier to set up.
In July, Moderna, an American firm that developed the successful mRNA covid-19 jab, the trial of his m beganRNA jab flu, which targets all four strains of the virus, is recommended World Health Organization. Pfizer, another American mRNA covid-19 vaccine maker has also adapted its technology to make the flu vaccine. The British drug company Seqirus has announced plans to begin clinical trials of its mRNA influenza vaccine in late 2022. She wants to use a messenger that amplifies itself RNA (SA-mRNA). Typical mRNA the vaccine tells human cells to produce an antigen (against which their immune system can produce antibodies). SA-mRNA vaccines also instruct the body’s cells to replicate mRNA yourself. This should mean that a much lower dose of the vaccine can lead to the same immunological outcome, which is useful if you need to be vaccinated against several flu viruses at once – or continue to boost immunity against Covid-19, which every winter should join the flu as usual. visitor. ■
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https://www.economist.com/international/measures-to-prevent-the-spread-of-covid-19-have-also-fended-off-flu/21804978
