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A pandemic happens when a disease spreads across many different countries or continents, impacting a large number of people. When you think of a pandemic, COVID-19 probably comes to mind.

However, in addition to the COVID-19 pandemic, we’ve also experienced another pandemic relatively recently: the 2009 H1N1 influenza pandemic.

You may be curious how these two pandemics compare with each other. Keep reading as we break down their similarities and differences below.

Before we go on to compare the two pandemics in more detail, here are some fast facts about each of them.

2009 H1N1 InfluenzaCOVID-19
Year started – year ended2009–20102020–present
Worldwide deathsabout 284,000 in the first 12 monthsabout 2,000,000 in the first 12 months
Virus2009 H1N1 influenza virusSARS-CoV-2 coronavirus
Transmissionrespiratory droplets and aerosols, contact with contaminated surfaces, asymptomatic spreadrespiratory droplets and aerosols, contact with contaminated surfaces, asymptomatic spread
Contagiousnessless contagious than COVID-19, contagious from 1 day before symptoms begin until 5 to 7 days after becoming sickmore contagious than 2009 H1N1 influenza, contagious from 2 days before symptoms begin until 10 days after testing positive
Symptomsfever and chills, fatigue, cough, body aches and pains, headache, sore throat, runny or stuffy nose, digestive symptoms like diarrhea and vomitingsimilar symptoms to 2009 H1N1 influenza, but also includes loss of smell and taste
Symptom onsetsudden after 1 to 4 daysgradual after 2 to 14 days
Age group most impactedpeople younger than 30adults over age 30
Illness severity94–98 percent mild80 percent mild, 20 percent severe or critical
Risk factorsbeing 65 years or older, being younger than 5 years old, being pregnant, having certain underlying health conditionsbeing 65 years or older, being pregnant, having certain underlying health conditions
Complicationspneumonia, worsening of underlying health conditions, secondary bacterial infections, respiratory failure, inflammation of tissues of the heart, brain, or muscles, injury to the kidneys or liver, acute respiratory distress syndrome (ARDS), sepsissame complications as 2009 H1N1 influenza, but also includes:
long-haul COVID-19, blood clots, multisystem inflammatory syndrome in children (MIS-C)
Treatmentssupportive care, FDA-approved antiviral medications like oseltamivir (Tamiflu)supportive care, FDA-approved antiviral remdesivir (Veklury), various treatments under Emergency Use Authorization
Vaccinesseveral vaccines developedseveral vaccines developed

Let’s look at some of the similarities between the 2009 H1N1 influenza and COVID-19 pandemics.


Both 2009 H1N1 influenza and COVID-19 can be transmitted in similar ways. These include:

  • Respiratory droplets and aerosols. These are tiny droplets that are made when a person who has the virus talks, sneezes, or coughs. If you inhale these droplets or aerosol particles, you can contract the virus.
  • Contaminated objects. Respiratory droplets containing virus can land on things like countertops and doorknobs. You can contract the virus by touching these things and then touching your mouth, nose, or eyes.

It’s also possible for a person to pass both viruses when they don’t have any symptoms. This is called asymptomatic transmission.


Both 2009 H1N1 influenza and COVID-19 are respiratory infections that share many symptoms in common. These can include:

One symptom that’s unique to COVID-19 is loss of smell and taste.

The 2009 H1N1 influenza and COVID-19 can range from mild to severe. In both pandemics, certain groups were at an increased risk for severe illness.

Risk factors

The groups at risk for complications from 2009 H1N1 influenza and COVID-19 have significant overlap. They include:

  • adults aged 65 and over
  • pregnant people
  • those with certain types of underlying health conditions

Underlying health conditions that can contribute to complications include:

Additional high risk groups for the 2009 H1N1 influenza

Some additional groups that were at a higher risk for serious illness during the 2009 H1N1 influenza pandemic included:

  • children under the age of 5
  • people under the age of 19 who were receiving long-term aspirin therapy

Additional high risk groups for COVID-19

Additionally, people with the following underlying health conditions are at a higher risk for severe illness from COVID-19:


Both 2009 H1N1 influenza and COVID-19 can lead to similar complications, including:

COVID-19 also has a few additional complications, including:


After the emergence of 2009 H1N1 influenza and COVID-19, efforts were quickly made to develop a vaccine.

Over the course of the 2009 H1N1 influenza pandemic, a total of five vaccines were approved by the Food and Drug Administration (FDA). These vaccines were developed using the same technology that had previously been used for seasonal flu vaccines.

According to the World Health Organization (WHO), over 200 COVID-19 vaccine candidates are in development at the time of this article, with at least seven different vaccines currently in use across the globe. They use a variety of different technologies, including:

Three vaccines are currently authorized by the FDA for emergency use in the United States. These include the vaccines produced by:

Now let’s explore the differences between the two pandemics.

The type of virus

The 2009 H1N1 pandemic was caused by an influenza virus. Influenza viruses are part of the viral family Orthomyxoviridae. Their genetic material consists of eight separate strands of RNA.

This specific influenza virus jumped to humans from pigs in 2009, hence its moniker “swine flu.” It actually contains RNA strands of human, swine, and avian origin. How does this happen?

Pigs can get several different types of influenza virus. When this happens, the RNA strands from the different viruses can mix together through a process called reassortment. This can create a unique influenza virus, such as the 2009 H1N1 virus.

COVID-19 is caused by a coronavirus from the viral family Coronaviridae. Its genetic material consists of a single strand of RNA. The specific virus that causes COVID-19 is called SARS-CoV-2.

The exact origin of SARS-CoV-2 is still unknown. A recently released report from the WHO indicates that SARS-CoV-2 probably originated in bats and was passed to humans through an unknown intermediate animal host.

2009 H1N1 influenza today

Even though the 2009 H1N1 influenza pandemic ended in 2010, these viruses continue to circulate today as seasonal flu strains. They’ve been included as one of the components of the seasonal flu vaccine each year since the pandemic.

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Worldwide deaths

In a 2012 study, researchers estimated that about 284,000 deaths occurred worldwide in the first 12 months of the 2009 H1N1 influenza pandemic. Since the end of the pandemic, the Centers for Disease Control and Prevention (CDC) estimated that an additional 75,000 deaths occurred in the United States due to 2009 H1N1 influenza.

COVID-19 has caused significantly more deaths worldwide. It’s estimated that about 2,000,000 deaths from COVID-19 occurred in the first 12 months of the pandemic.

As with 2009 H1N1 influenza, deaths due to COVID-19 will continue during and after the pandemic. At the time of writing, COVID-19 has caused almost 3,000,000 deaths worldwide. Over 500,000 deaths have occurred in the United States.


COVID-19 is more contagious than 2009 H1N1 influenza. This means that COVID-19 can spread more easily between individuals.

It’s estimated that the R0 for COVID-19 is about 3 while the R0 for 2009 H1N1 influenza is between 1.3 and 1.7. “R0” stands for “basic reproduction number.” It reflects the number of other people who are susceptible to contracting the virus if one person has it.

So, one person who’s developed COVID-19 may potentially transmit the virus to three other people. Meanwhile, a person that has 2009 H1N1 influenza may pass it to between one to two other people.

The period of contagiousness between the two viruses can also vary:

  • Flu: A person who has the flu can typically pass the virus from 1 day before symptoms start until 5 to 7 days after becoming ill.
  • COVID-19: COVID-19 can be passed about 2 days before symptoms start. Whether or not symptoms are present, a person can pass the virus for up to 10 days after testing positive.

Symptom onset

Flu, including the 2009 H1N1 flu, and COVID-19 differ when it comes to symptom onset:

  • Flu: The incubation period for flu can range from 1 to 4 days. When symptoms occur, they often come on suddenly.
  • COVID-19: COVID-19 has a longer incubation period, ranging from 2 to 14 days, although many people develop symptoms 5 days after contracting the virus. Symptoms typically appear more gradually.

Age group most impacted

The two pandemics also differed in the age groups that were most impacted:

  • 2009 H1N1 influenza: People under the age of 30 were most impacted by the 2009 H1N1 influenza pandemic. It’s believed that this is due to pre-existing influenza immunity in older people.
  • COVID-19: Adults aged 30 and over have been most impacted by the COVID-19 pandemic. Generally speaking, fewer and less severe cases have been observed in younger people.

Illness severity

It’s estimated that between 94 and 98 percent cases of 2009 H1N1 influenza were mild. Much fewer people experienced severe or critical illness.

A higher percentage of people who develop COVID-19 have severe illness. The WHO estimates that, while COVID-19 is mild 80 percent of the time, 20 percent of people who contract the virus can become seriously or critically ill.


The treatment for 2009 H1N1 influenza included supportive care and antiviral medications. Supportive care involves:

  • getting enough rest
  • drinking plenty of fluids
  • using over-the-counter (OTC) medications like acetaminophen (Tylenol), ibuprofen (Advil, Motrin), and naproxen (Aleve) to ease symptoms like fever and pain

The H1N1 virus was also susceptible to antiviral medications that had been previously used (and are still used) for seasonal flu, such as oseltamivir (Tamiflu) and zanamivir (Relenza).

When COVID-19 first emerged, however, we didn’t know of any treatments that were effective against it. Over time, various therapies have either been approved by the FDA or authorized for emergency use.

Mild to moderate COVID-19 is often treated with supportive care. Additional treatments are also available to people who are hospitalized or at a high risk of serious illness. These can include:

  • remdesivir (Veklury), the only FDA-approved antiviral treatment for COVID-19
  • SARS-CoV-2-neutralizing antibodies
  • dexamethasone, a type of steroid medication
  • COVID-19 convalescent plasma

We’ve experienced two different pandemics in the 21st century: the 2009 H1N1 influenza pandemic and the COVID-19 pandemic. There are various similarities and differences between these two pandemics.

Although they’re caused by different viruses, both 2009 H1N1 influenza and COVID-19 are respiratory illnesses that are transmitted in the same way. There’s also a lot of overlap in symptoms, complications, and risk factors for serious illness.

However, COVID-19 is more likely to cause serious illness than 2009 H1N1 influenza and has led to more deaths worldwide. It’s also more contagious than 2009 H1N1 influenza.

While effective treatments weren’t known at the beginning of the COVID-19 pandemic, we now have several that are available. Additionally, as in the 2009 H1N1 influenza pandemic, vaccines have been rapidly developed for COVID-19.