https://www.economist.com/blogs/economist-explains/2018/02/economist-explains-4
It may be the deadliest in nearly a decade
THE 2017-18 flu season, which lasts, roughly, for the duration of the northern hemisphere’s autumn and winter, may end up being as deadly as the swine-flu pandemic (猪流感) of 2009. Pneumonia (肺炎) and influenza (流行性感冒) caused nearly 10% of all deaths in the week ending January 13th, which exceeds the definition for an epidemic (传染病；流行病), as used by the Centres for Disease Control and Prevention (CDC). The recent hospitalisation rate for flu or pneumonia, 51 per 100,000 people, is at its highest for this time of year since more accurate tracking began in 2010. More than 50 children have already died in America. Why is this season’s flu so nasty (难对付的)?
The flu pandemic of 1918-20 invariably looms over such discussions. It infected 500m people, and killed between 50m and 100m. The situation in some cities was said to resemble an outbreak of bubonic plague (腺鼠疫，腺鼠疫，黑死病). A shortage of coffins and a failure to collect all corpses led some parents to put their dead children into large macaroni boxes, notes Jen Wright, author of “Get Well Soon”, a book surveying historical epidemics. The pandemic seems to have hit so hard because it was a new variant to which people had little immunity. Spotting new strains ([微] 菌株) before they hit is difficult, so the risk of such outbreaks remains. “We don’t really have a good way of predicting when the next influenza pandemic will come along,” says Yonatan Grad, a professor of immunology (免疫学) and infectious diseases at Harvard's School of Public Health.
While not a pandemic of the 1918 sort, this season’s flu has been made worse by several factors. Its dominant strain is the old but virulent (剧毒的) H3N2 subtype. Identified 50 years ago, this is prone to the kind of rapid mutation that allows it to evade the defences the body created against previous variants. As a result, the current flu vaccine, developed early last year, has been less effective than usual. Reports from Australia, where the flu season arrives half a year earlier than in the north, plus early analysis from Canada, indicate efficacy (功效) against H3N2 as low as 10%, instead of the more typical 30%-60%. Flu can kill, but it also weakens the immune system against secondary infections, notably bacterial pneumonia. This season, it appears that flu victims have been hit by more respiratory (呼吸的) viruses than normal. A recent paper also notes that the situation has been exacerbated [加重（病情，痛苦等）] by a reduction in vaccination rates (because of disproven worries about the safety of vaccines) and increased antibiotic resistance.
Flu-related research has improved, however. Even when not highly effective, the vaccine cuts incidence, severity and transmission, and anti-viral medication reduces the duration and impact of the illness. But, along with education campaigns to augment vaccination rates, further improvements to the vaccines are possible. Most flu vaccines rely on cultivation in chicken eggs. Dr Grad notes that this may cause them to mutate to the conditions inside the eggs, thus reducing their effectiveness as antigens ([免疫] 抗原). For years researchers have worked towards switching from chicken cells to other animal and insect proteins. The holy grail (圣杯), however, is a universal flu vaccine that would be effective against both seasonal and pandemic flu outbreaks. One tactic involves trying to disable the flu virus by knocking out its relatively stable stem, rather than its head (the part that mutates). Alternatively, using a genetically engineered live virus may trigger a more robust, more persistent response from the immune system. A breakthrough may not be imminent, but thousands of coughing, wheezing sufferers would be glad to hear some good news.
