For two years it raged across the world, infecting 500 million people — a third of all the people on earth — and killing 50 million. And then, the Spanish flu just seemed to fade away. The rate of infections and deaths dropped sharply through March and April of 1919.
So what ended it?
It wasn’t a vaccine, of course. Even if they could have developed one in 1918, scientists didn’t even know if the pandemic was caused by bacteria or a virus, and wouldn’t know until 1930.
Public health officials had little choice but to give the virus fewer chances to spread. Social distancing, mask-wearing, frequent hand washing, isolating patients, and closing public venues all worked to hem in the virus.
Another factor in the pandemic’s end was the nature of viruses. Some viruses continually mutate in a process called “antigenic drift or shift,” which could enable them to develop into a deadly strain that is immune to human antibodies.
But they can also mutate into a less deadly version. The Spanish flu didn’t die off but “drifted” into an altered form.
In the winters of 1919-1920 and 1920-1921, the Spanish flu made a comeback, but it had now morphed into a less virulent virus, whose symptoms were almost identical to a seasonal flu.
In fact, the influenza strain that causes the Spanish flu has remained with us, becoming the agent responsible for our routine winter illnesses. It is benign, compared to its deadly 1918 form.
We are, of course, still susceptible to flu viruses. In the last 10 years, the annual death rate from flu has ranged from 12,000 to 61,000.
Occasionally, the flu virus combines genetic material with a swine flu or bird flu to create a deadly new form (this is the more abrupt antigenic “shift”). In 1957, an H2N2 virus combined with an avian flu virus to produce the Asian flu, killing 1-4 million people worldwide. Because the virus was new, few people had immunity. In 1968, another combination with avian flu resulted in the H3N2 Hong Kong flu. The H3N2 virus continues to circulate worldwide as a seasonal influenza A virus. In 2009, a combination with a porcine virus produced the swine flu epidemic of that year.
Each had some element of the 1918 Spanish flu.
The ideal solution for the flu or other deadly viruses would be to rid the world of them completely. But, as Dr. Kirsty Short from Australia’s University of Queensland told ABC News, getting a virus out of the human population is incredibly difficult: “We’ve only ever done it with one human pathogen, and that’s smallpox.” It took a global immunization campaign, with a vaccine that was 100 percent effective against smallpox and any mutation of the virus.
The idea of achieving herd immunity by simply stepping back and allowing a virus free rein to infect everyone wouldn’t work, either. Dr. Howard Markel of the University of Michigan told WebMD, “you would never get levels of 60 percent to 90 percent, which is what people are estimating you would need.”
Dr. Jeffrey Shaman, an epidemiologist at Columbia University, estimates that 105 million Americans — about a third — have contracted the coronavirus. Our population hasn’t yet reached the 70 percent needed for herd immunity to start reducing the number of infections. But this assumes that, once infected or immunized, people with remain immune to further infection.
If all goes well and we are able to administer President Biden’s goal of 1.5 million shots per day, the United States could achieve herd immunity by November of this year, according to Reuters’ calculations. But much of that depends on the number of people who are willing to be vaccinated. As Director of National Institute of Allergy and Infectious Diseases Anthony S. Fauci has said, “if only 40 to 50 percent of people in society get vaccinated, it’s going to take quite a while…to get to that blanket of herd immunity.”
Or we could get lucky and the virus could mutate to a less deadly strain, like the Spanish flu did. Fortunately, advances in science over the last hundred years mean that we no longer have to rely on luck alone.
Featured image: Everett Collection / Shutterstock
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