Comparing COVID-19 with previous pandemics
21 Apr, 2020Pandemics have played a role in shaping human history throughout the ages. Few people reading this today will remember outbreaks on this scale, but history shows us that although it is devastating, what we are experiencing now is nothing unusual.
First, for clarity, it is worth explaining what “pandemic” means. The World Health Organization (WHO) define a pandemic as “the worldwide spread of a new disease.”
Now, we will touch on the other pandemic that is still under way.
1981–present: HIV
With vast improvements in treatment, information, diagnostic capabilities, and surveillance in Western countries, it is easy to forget that experts still class HIV as a pandemic.
Since the early 1980s, HIV has claimed the lives of more than 32 million people. At the end of 2018, around 37.9 million people were living with HIV.
Although HIV is also caused by a virus, there are significant differences between the two current pandemics; the most obvious being their means of transmission. Unlike SARS-CoV-2, which is the virus that causes COVID-19, HIV cannot transmit via coughs and sneezes.
Comparatively, COVID-19 spreads through communities much more easily. Within a matter of weeks, SARS-CoV-2 made it to every continent on Earth except Antarctica.
Another important difference is that there are currently no drugs that can treat or prevent COVID-19. Although there is no vaccine for HIV, thanks to antiretroviral medications, people who have access to care can now live long and healthy lives.
2009–2010: H1N1 swine flu
According to the Centers for Disease Control and Prevention (CDC), between April 2009 and April 2010, the swine flu pandemic affected an estimated 60.8 million people. There were also around 274,304 hospitalizations and 12,469 deaths.
Both swine flu and the novel coronavirus cause symptoms such as fever, chills, a cough, and headaches.
Like SARS-CoV-2, the (H1N1)pdm09 virus was also significantly different from other strains. This meant that most people did not have any natural immunity.
Interestingly, however, some older adults did have immunity, suggesting that (H1N1)pdm09 or something similar might have infected large numbers of people a few decades before. Because of this immunity, 80% of the fatalities occurred in people younger than 65.
This is not the case with SARS-CoV-2; all age groups seem to be equally likely to contract it, and older adults are most at risk of developing severe illness. It is possible that certain groups of people have a level of immunity against SARS-CoV-2, but researchers have not yet identified such a group.
The overall mortality rate of swine flu was around 0.02%. According to recent estimates, which are likely to change as the pandemic progresses, this is somewhat lower than that of COVID-19. Also, swine flu was less contagious than COVID-19.
The basic reproduction number (R0) of swine flu is 1.4 to 1.6. This means that each individual with swine flu is likely to transmit the virus to an average of 1.4 to 1.6 people. In contrast, scientists believe that the R0 of COVID-19 is between 2 and 2.5, or perhaps higher.
The many returns of cholera
Over the past 2 centuries, cholera has reached pandemic proportions seven times. Experts class the cholera pandemic of 1961–1975 as the seventh one.
Cholera is a bacterial infection of the small intestine by certain strains of Vibrio cholerae. It can be fatal within hours. The most common symptom is diarrhea, though muscle cramps and vomiting can also occur.
Although immediate rehydration treatment is successful in up to 80% of cases, the mortality rate of cholera can be up to 50% without treatment. This is many times higher than even the highest estimates for COVID-19. Cholera occurs when a person ingests contaminated food or water.
The seventh pandemic was caused by a strain of V. cholerae called El Tor, which scientists first identified in 1905. The outbreak appears to have begun on the island of Sulawesi in Indonesia. From there, it spread to Bangladesh, India, and the Soviet Union, including Ukraine and Azerbaijan.
By 1973, the outbreak had also reached Japan, Italy, and the South Pacific. In the 1990s, though the pandemic had officially ended, the same strain reached Latin America, a region that had not experienced cholera for 100 years. There, there were at least 400,000 cases and 4,000 deaths.
As with COVID-19, hand-washing is essential for stopping the spread of cholera. However, to prevent cholera, access to safe water and good food hygiene are just as important.
1918: The Spanish flu
In the spring of 1918, health professionals detected an H1N1 virus in United States military personnel.
From January 1918 to December 1920, this virus — which appears to have moved from birds to humans — infected an estimated 500 million people. This equates to 1 in 3 people on Earth. The virus killed around 675,000 people in the U.S. alone and approximately 50 million worldwide.
This strain of influenza, like COVID-19, transmitted via respiratory droplets.
As with COVID-19, older adults were most at risk of developing severe symptoms. However, in stark contrast to COVID-19, the Spanish flu also impacted children under the age of 5 and adults aged 20–40.
In fact, a 25-year-old was more likely to die from the Spanish flu than a 74-year-old was. This is unusual for flu.
COVID-19, however, generally affects children in relatively minor ways, and adults aged 20–40 are significantly less likely to develop severe symptoms than older adults.
As with swine flu, it may be that older adults at this time had a preexisting immunity to a similar pathogen. Perhaps the 1889–1890 flu pandemic, or the Russian flu, afforded some protection to those who survived it.
Additionally, some scientists believe that younger people’s vigorous immune responses might have led to more severe lung symptoms due to “exuberant pulmonary exudation.” In other words, the strong immune responses of young people may produce excess fluid in the lungs, making breathing even more difficult.
At the time, there were no vaccines to prevent the disease and no antibiotics to treat the bacterial infections that sometimes developed alongside it. The virulent nature of this particular H1N1 strain and the lack of medication available made this the most severe pandemic in recent history.
The pandemic came in two waves, with the second being more deadly than the first. However, rather abruptly, the virus disappeared.
The Spanish flu had a mortality rate of around 2.5%. At this stage, it is difficult to compare that with COVID-19 because estimates vary.
To understand why mortality rates are so difficult to calculate, Medical News Today recently published an article on the topic.
