Comparing COVID-19 with previous pandemics

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.

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.

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.

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.

A different time

The Spanish flu’s high mortality rate was, in part, due to the virulence of the virus.

Social differences also played a role. In 1918, people tended to live in close quarters and perhaps did not value hygiene as much. These factors can influence how quickly a virus spreads and how lethal it can be.

Also, the world was at war, meaning that large numbers of troops were traveling to distant locations and aiding the spread. In peacetime, someone who is very ill will stay at home, whereas someone who is only a little under the weather might continue as normal.

During World War I, malnutrition was common for both those at home and those on the frontline. This is yet another factor that may have made people more susceptible to disease.

The Spanish flu and physical distancing

Although the Spanish flu pandemic has many differences to today’s COVID-19 pandemic, it teaches us a valuable lesson about the effectiveness of quickly implementing physical distancing measures, or social distancing measures.

In Philadelphia, PA, officials downplayed the significance of the first cases in the city. Mass gatherings continued and schools remained open. The city only implemented physical distancing and other measures around 14 days after the first cases appeared. This had significant consequences.

In contrast, within 2 days of its first reported cases, St. Louis, MI, moved quickly to implement physical distancing measures.

As one author writes, “The costs of [Philadelphia’s] delay appear to have been significant; by the time Philadelphia responded, it faced an epidemic considerably larger than the epidemic St. Louis faced.”

In 2002, severe acute respiratory syndrome (SARS) became the first pandemic of the 21st century. Like COVID-19, SARS was due to a coronavirus, known as SARS-CoV. It also originated in China.

Scientists believe that SARS-CoV-2, the virus that causes COVID-19, originated in bats, moved into pangolins, then entered humans. Similarly, SARS-CoV began in bats, but it moved into civets before humans.

Both SARS-CoV and the virus that causes COVID-19 can transmit via droplets from coughs and sneezes.

Globally, SARS infected an estimated 8,000 people in 29 countries and had a mortality rate of around 10%. By most estimates, this is higher than COVID-19’s mortality rate.

Both SARS and COVID-19 affect older adults more severely than they do younger individuals. Around half of those over 65 who contracted SARS died, compared with just 1% of people under 24.

However, COVID-19 seems to be more infectious than SARS and has already spread to far more countries and killed more people than SARS.

How did we eradicate SARS?

In short, surveillance, the isolation of those who contracted it, and strict quarantine measures halted the progress of SARS. As one paper puts it, “By interrupting all human-to-human transmission, SARS was effectively eradicated.”

The question is, can we eliminate COVID-19 in the same way? In answer to this question, the authors write:

“COVID-19 differs from SARS in terms of infectious period, transmissibility, clinical severity, and extent of community spread. Even if traditional public health measures are not able to fully contain the outbreak of COVID-19, they will still be effective in reducing peak incidence and global deaths.”

No article on pandemics would be complete without mentioning the Black Death, also referred to as The Plague.

Peaking in Europe between 1347 and 1351, the Black Death was responsible for an estimated 75–200 million deaths. In fact, it may have killed half of the entire population of Europe.

This pandemic was caused by a bacterium, called Yersinia pestis, rather than a virus. Epidemiologists believe that the Black Death also originated in Asia.

Like COVID-19, plague transmits via respiratory droplets. However, the Black Death’s march across the planet was enabled by rodents rather than the movement of humans.

Rodents carrying bacteria-infected fleas spread this disease. Y. pestis partially blocks the guts of fleas. As the fleas feed on a human, they attempt to clear their blocked guts by regurgitating their meal. This effort releases Y. pestis into the vicinity of the flea’s bite wound.

Though much rarer, plague still exists, particularly in low income regions. The majority of cases now occur in Africa. Thanks to improvements in medicine and hygiene, the disease has not reached pandemic proportions since the Black Death.

Without treatment, the case-fatality ratio can be 30–100%. In the U.S., the mortality rate of plague before antibiotics was 66%. By 1990–2010, modern medicine had reduced this figure to a still-high 11%.

The Black Death pandemic eventually waned, and this seems to have been for a few reasons. People began to self-quarantine, and they stopped traveling as freely through fear of catching the disease.

People also started to hold fragrant handkerchiefs against their mouths when in public, and this might have reduced the risk of infection and transmission.

Although there are significant differences between the pandemics above and COVID-19, there are some key takeaways here.

Surveillance is important — we need to know who is affected and who has been affected. Indeed, testing is key to our understanding of COVID-19 and how to slow its progress.

We have also learned that physical distancing and quarantine measures work.

Where a pandemic happens, both geographically and historically, also makes a difference. Would the Black Death have been so devastating had the people of the time had access to modern medical treatments, an understanding of how germs spread, and improved nutrition? Probably not.

It may be of little consolation, but it might help some of us, psychologically, to remember that we are not the only humans to have experienced such trials and tribulations — and we will not be the last.

It is also important to remember that pandemics do end, and that modern science and medicine can be incredible forces for good. We no longer live in the Dark Ages; we are better armed today than we have ever been.