Seven times when the flu was lethal
One hundred years ago, the Spaniard killed five percent of the planet’s population. But it was not the only time in history where an influenza pandemic has made millions of deaths.
The influenza virus changes slightly every year, and the small mutations in the proteins on its surface are not recognized by our antibodies: this is the reason that the flu affects several times in the course of life. But sometimes it happens that the mutations to which the virus goes are more important, or that a new virus emerges from the hybridization of two different strains that have infected the same host.
In this case, the immune system of people is unprepared: the infections spread much more quickly and it happens that to die of flu are also young and healthy people. Those who survive acquire immunity against the virus, which in turn becomes one of the “normal” ones in circulation in seasonal influenza. Until again it does happen that another emerges so different from being able to trigger a pandemic. In addition to Spanish, it has happened other times in the past.
In 1510 the first case of what is thought to have been an influenza pandemic is documented. All over Europe there are cases of a disease with fever, cough, and tightness in the chest. We do not know which virus it was and the number of deaths can only be speculated, but it is likely that it is an important contagion, for the time.
The first global pandemic dates back to 1889-90 and spread also thanks to modern means of transport: trains and ships. The first cases occurred in Russia, in St. Petersburg, and after just over two months there was a peak in the United States: one million people died because of the flu. It was probably caused by the H3N8 virus, perhaps linked to that (H3N2) which is now raging in several European countries .
In 1957-58, forty years after the Spanish, it was the turn of Asian influence. In that case the flu virus that caused the pandemic was H2N2, a recombination (probably occurred in a pig) of the Spanish virus with another bird flu virus. The deaths were more than a million: to be infected were mainly the youngest, born after 1918, and therefore not endowed with at least a certain immunity to the emerging virus.
Ten years later, in 1968-69, the Hong Kong influence spread. The first cases were probably in China, but given the regime of secrecy in the country the news of the infections appeared only when the virus arrived in Hong Kong. Even in this case, the previous pandemic virus had become one of the “normal” viruses in circulation, but it had emerged a more aggressive by hybridization with a strain present in birds: it is the H3N2 virus that is still in circulation and dominates the current flu season in several European countries.
The red flu appeared in Russia in November 1977: it was a virus of the H1N1 type practically identical to one already circulated in the fifties. It is thought that the virus has escaped into the environment from laboratory experiments for a vaccine. The younger people had no immunity, so they caused many infections, but the effects were not serious.
2009 was the year of swine flu, caused by a virus of the subtype H1N1, which until then caused the disease only in pigs. It appeared for the first time in Mexico, but now it regularly circulates among normal flu viruses, so much so that it is also included in this year’s vaccine. The excess deaths for the 2009 pandemic were 300-400 thousand.