截至北京时间4月8日上午8时，据美国约翰斯·霍普金斯大学实时疫情数据显示，全球新冠肺炎累计确诊病例逾142万，达1428428例；累计死亡破8万；累计治愈超30万例。

而在102年前，“西班牙大流感”曾造成了2500万人死亡；而本世纪的研究表明，这场“人类的灾难”让大约5000万-1亿人失去了生命。

“西班牙流感”的症状非常“可怕”——人的肺部遭到病毒攻击后，耳朵和鼻子都会向外喷血，皮肤也会变成蓝色或紫色。感染者要么死于病毒，要么死于身体对病毒产生的强烈免疫反应。

传统的解释认为，这场流感最早出现于美国的堪萨斯，随后在全美以及欧洲等各地的一战战壕中出现，进而波及全球——而它之所以被叫做“西班牙流感”，是因为这场瘟疫最先被西班牙媒体记录了下来。但实际上，目前学界对于这场流感的发源地，以及传播路径依然存在争议。

特别值得关注的是，“西班牙流感”的二次爆发—— 在1918年年底，人们一度以为，已经传播了几个月的西班牙流感进入到了衰减期。但转眼到了第二年，却突然出现了致死性更强的毒株，它的传播速度“像野火一样”，并快速波及了全球约全球四分之一的人口.....直到1920，1921年，整个疫情才彻底宣告消退。

值得一提的是，即便大规模的疫情会消散，但严格来说，一种流感病毒几乎是不可能根除的。因为它在不断变异，继续传播。后来的研究证实，这种病毒直到1957年还在持续人传人.....

这场上个世纪最为惨烈的流感，几乎正好发生在一百年前。或许总结过去，能为今天的人们带来一些经验吧！

剑桥大学教授回顾1918年西班牙大流感

Perhaps until recently, Spanish Flu has been what some people call a "forgotten pandemic.  But it was a huge global calamity. In terms of the number of deaths we re saying 50 to 100 million - far greater than the casualties of the first world war.

Roughly around May, April May 1918 when you know the carnage of the First World War is is graphic and horrendous but at the same time this this unknown enemy is starting to sweep through the US, Europe, the trenches and it is recorded by the Spanish press and it becomes dubbed as the  Spanish flu  because they are neutral.

Well at the time in the 1920s they estimated that maybe 20 million had died. By the late 20th century that figure it went up to 25 million. In the 21st century with scientists and historians now getting together to work much more closely, that figure has now been upped to fifty to a hundred million people killed. This virus killed more people in the first 25 weeks than HIV/AIDS has killed in 25 years - horrendous! Those mortality statistics are staggering.

We don t know exactly why some flu strains are much more severe than others and why some of them would would be more likely to kill people or cause very severe disease. What is particular about avian and pandemic viruses is that they replicate deep inside our lungs. When our cells detect this they trigger very strongly an immune response this leads to an influx of white blood cells and fluids into our lungs and it restricts the amount of air space that we have to breathe.

The symptoms are very graphic and very very striking so you know it s said that some people drowned in their own phlegm, so if it was hitting or effecting the lungs - people were spurting blood from their ears and their noses. Descriptions of people turning blue or purple so you know it was really really severe and people just dropping down in the streets

Those that succumbed to the flu were in the age group 20 to 40 years which is very unusual for an influenza epidemic or pandemic and scientists and historians are now still looking to see why. There s really two ways that people died in 1918 they either died from the initial flu infection or they died from a enormously strong immune response to that virus were their lungs just filled up with fluids from trying to attack the virus that got into their lungs.

So traditionally everyone sort of said oh well it s the trenches you know the conditions of the war and that s why it was so fatal but when you think well you know how did it spread so rapidly around the world to places that are not part of the theatre of war. I think the traditional explanation is it starts in Kansas in an army camp and then the troops bringing it over to the trenches, Europe but there s still so many, many unknowns.

So mathematical modelers have long been interested in the 1918 pandemic and one of the questions is to try and disentangle how its spread around the world and exactly what the routes have been. Given a perfect data you could work backwards and try to infer where it s come from. Whereabouts does it arrive in a country, does it arrive multiple times or thinking about multiple countries where is the first place?

If you understand the origin of a pandemic then you understanding about where it s come from and maybe you can stop that in future. Almost certainly it was a bird flu originally but then we also know that that flu or something very similar to it was in pigs at the same time.

Maybe it s somebody who works very closely with birds or who works very closely with pigs or has some other exposure like that. One of the big really open questions in flu research and flu Public Health is - How does the virus adapt from one species to another, how does for example a virus in pigs or in Birds get into humans and then start transmitting?

Then the key question is - how does the virus then adapt within that person to stop being a pig virus or a bird virus and become a human virus? in other words to be able to transmit from human to human and it s probably some very quick evolutionary process that is going on within that human and in many cases won t be successful, but in a few cases we ll and that s when the virus can start spreading between humans and become a flu pandemic and then stay in humans as regular seasonal flu.

Just as people were celebrating Armistice Day and there was hope that it was dying down but then it resurged and a far more deadly and virulent strain emerged.

So this the second wave really spread like wildfire affecting a third or quarter of the population of the world and it was short-lived so it petered out not long afterwards maybe in 1920/1921 but it was it was in the sense short-lived. What happened was is that virus continued to transmit among humans, in fact it continued until 1957 to transmit between humans and probably what happened there is that the virus adapted to humans. It wasn t this avian or swine virus that came in and was accidentally more pathogenic in humans.

In a lab here in Cambridge we study both seasonal flu and pandemic flu from the standpoint of - how does the virus evolve? And how can we predict that evolution and make vaccines to try to artificially evolve the virus both in the laboratory and in the computer to understand what its gonna do next and to make vaccines against those strains that will evolve in the future.

So this is the basic science of studying evolution trying to predict that evolution. Something that s nobody has ever been able to do for a complex organism. And then working to use that understanding to make better vaccines.

On the pandemic flu side we do a similar thing where we look to see how that virus is changing - that virus how it changes in birds and how it changes in birds and in other species and to try to see what possible variants out there might be but there might be and again to make vaccines that could protect against all of those variants that we see. Flu is very difficult to eradicate because it s constantly mutating and changing its genetic information.

We work on the influenza virus and in particular on the enzyme that copies the genetic information of the virus when this enters our cells. Specifically we re interested in how this enzyme can do this activity and how it inserts mutations in a viral genome that leads to the formation of the new strains to which we need to develop new vaccines. And we are also interested in when this enzyme messes up how it triggers the innate immune resistant and helps cause disease.

We really don t know why we haven t seen a pandemic as deadly the 1918 pandemic. Scientists and public health officials are extremely concerned the national risk register which is the way that our government plans what are all the risks to civil society in the UK.

There s only two events that are up there in terms of the most catastrophic and that s a terrorist event or a influenza pandemic. There is a real threat that there can be such pandemics for example the H5 in the H7 flu viruses that have infected now close to 2,000 people and killed about half of them.

There has been with the H7 viruses some transmission from human to human not very efficient and it hasn t really taken off. If either of those viruses did adapt to really transmit well between humans, there s a real concern that it could be as bad as the 1918 virus and this is why there is so much research done for the public good to try to understand what s happening and so much work done by people in public health and preparing in hospitals in case something like that happens.

Well experts like to say it s not if- but when? Coming at it as a mathematician it s happened a lot of times in the past, it ll probably happen again. The 1918 pandemic is difficult because of lack of data but the most recent influenza pandemic we had was in 2009 and from that pandemic there is some very good data. If we understand how the 2009 pandemic spread maybe that tells us something we can use to help control future pandemics.

We can t stop them, the alternative is at least to allocate our resources better to try and reduce the number of cases in each place. Looking back a hundred years to the last pandemic also invites the question of - a hundred years from now what will we be like in terms of how well we are protected against flu? Or what things we could do to protect ourselves in some situations? Surely we ll be in a situation where we know more about what viruses are in the world and where they are, surveillance will be so much better.

Surely we ll be in a better situation where we have better drugs and better vaccines because we know more about the virus so we know more about its weaknesses, we know more about our immune systems and we know how to enable them to fight those pathogens better. At some point we will have a universal vaccine that will protect us against flu for the rest of our lives. When this is is a whole other question. There are a great number of approaches and really good ideas to doing this.There are already attempts at this that are at a quite advanced stage. It might be ten years from now, it might be twenty or thirty or forty years from now we really don t know.