Swine flu spreads mainly through respiratory droplets from coughing and sneezing, and it can move fast through communities. During the 2009 H1N1 pandemic, the United States saw an estimated 60.8 million symptomatic cases (April 2009–April 2010). Symptoms vary by person: in adults, fever was present in 94% of confirmed cases, and muscle pain affected 60% of hospitalized patients. This guide explains key symptoms, transmission patterns, prevention, and how antivirals like oseltamivir and combination therapy may influence outcomes.
Key Takeaways
- Fever was present in 94% of confirmed swine flu cases in adults
- Cough occurred in 92% of pediatric swine flu patients
- Sore throat was reported in 66% of swine flu cases per CDC data
- In the United States, the 2009 H1N1 swine flu pandemic resulted in an estimated 60.8 million symptomatic cases between April 2009 and April 2010
- Globally, the World Health Organization estimated between 151,700 and 575,400 swine flu-related deaths during the 2009 pandemic
- Mexico reported the first confirmed cases of swine flu with 132 deaths by April 26, 2009
- Over 90 million doses of swine flu vaccine were administered in the US by February 2010
- The swine flu vaccine efficacy was 68% against hospitalization in children
- Single-dose swine flu vaccine provided 76% protection in adults 18-64 years
- Swine flu primarily spread via respiratory droplets from coughing/sneezing
- One infected person could spread swine flu to 1.4-1.6 others (R0)
- Household secondary attack rate for swine flu was 9.5%
- Oseltamivir reduced swine flu symptom duration by 1 day in uncomplicated cases
- Early oseltamivir (within 48 hours) lowered hospitalization risk by 55% in outpatients
- Swine flu ICU mortality was 14.3% despite antiviral treatment
Fever, cough, and sore throat were common, with millions infected and global deaths during 2009 H1N1.
Related reading
01 · Category
Clinical Features And Diagnosis24 stats
01
Fever was present in 94% of confirmed swine flu cases in adults
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Cough occurred in 92% of pediatric swine flu patients
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Sore throat was reported in 66% of swine flu cases per CDC data
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Myalgia (muscle pain) affected 60% of hospitalized swine flu patients
05
Fatigue was noted in 77% of swine flu outpatients
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Headache incidence in swine flu was 73% in adults
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Diarrhea occurred in 25% of swine flu cases, higher than seasonal flu
08
Vomiting was seen in 27% of pediatric swine flu patients
09
Shortness of breath reported in 30% of severe swine flu cases
10
Rhinorrhea (runny nose) in 57% of swine flu children
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75% of swine flu patients had fever >100°F (37.8°C)
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Conjunctivitis appeared in 15-20% of swine flu cases
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Lymphopenia (low lymphocytes) found in 70% of hospitalized swine flu patients
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Thrombocytopenia (low platelets) in 25% of severe cases
15
Elevated C-reactive protein (>10 mg/L) in 90% of swine flu ICU patients
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Chest X-rays showed bilateral infiltrates in 80% of fatal swine flu cases
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PCR sensitivity for swine flu diagnosis was 92-100% from nasopharyngeal swabs
18
Rapid influenza diagnostic tests (RIDT) had 44-66% sensitivity for swine flu
19
Viral culture confirmation took 3-10 days for swine flu
20
Serologic testing showed 4-fold antibody rise in 95% of convalescent swine flu patients
21
Swine flu incubation period averaged 2 days (range 1-4 days)
22
Neurological symptoms like seizures occurred in 5% of pediatric swine flu cases
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Myocarditis was autopsy-confirmed in 6% of swine flu deaths
24
Guillain-Barré syndrome risk was 1.7 excess cases per million swine flu vaccinations
Interpretation
Clinical Features And Diagnosis Interpretation
Clinical features for swine flu strongly cluster around common respiratory and systemic symptoms, with fever in 94% of adults and cough in 92% of pediatric cases, helping diagnosis by aligning CDC sore throat reports of 66% and high rates of fatigue and myalgia across patients.
02 · Category
Epidemiology And Surveillance29 stats
01
In the United States, the 2009 H1N1 swine flu pandemic resulted in an estimated 60.8 million symptomatic cases between April 2009 and April 2010
02
Globally, the World Health Organization estimated between 151,700 and 575,400 swine flu-related deaths during the 2009 pandemic
03
Mexico reported the first confirmed cases of swine flu with 132 deaths by April 26, 2009
04
By June 19, 2009, WHO confirmed 27,737 swine flu cases across 74 countries with 141 deaths
05
The US CDC laboratory confirmed 43,771 swine flu cases by June 2009
06
In the UK, swine flu caused 457 deaths by August 2010 according to official figures
07
Brazil recorded 2,060 swine flu deaths during the 2009-2010 season
08
Australia had 6,013 laboratory-confirmed swine flu cases in 2009 with 191 deaths
09
The case fatality rate (CFR) for swine flu was estimated at 0.4% globally by WHO
10
In the US, swine flu hospitalizations peaked at over 30,000 per week in October 2009
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Canada reported 8,135 hospitalized swine flu cases and 428 deaths by April 2010
12
India saw 28,954 swine flu cases from 2009-2015 with 1,763 deaths
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The swine flu virus was detected in pigs in 11 US states by November 2009
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Europe had over 3 million swine flu cases estimated by ECDC in 2009
15
Japan confirmed 4,188 swine flu cases by July 2009
16
South Africa reported 30,000 swine flu cases with 282 deaths in 2009-2010
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The median age of swine flu deaths in the US was 37 years, much younger than seasonal flu
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Pregnant women had a 4-fold increased risk of swine flu hospitalization in the US
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Children under 18 accounted for 40% of US swine flu hospitalizations
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Obesity increased swine flu ICU admission risk by 2.4 times
21
By October 2009, WHO declared swine flu no longer a pandemic phase 6 but post-pandemic
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Argentina reported 586 swine flu deaths in 2009
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Chile had 1,093 confirmed swine flu deaths by 2010
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New Zealand recorded 199 swine flu deaths
25
Egypt banned pig farming in response to early swine flu fears, affecting 4 million pigs
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The R0 (basic reproduction number) for swine flu was estimated at 1.4-1.6
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US indigenous populations had swine flu hospitalization rates 4 times higher than average
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France estimated 11 million swine flu cases with 434 deaths
29
Russia reported 37 swine flu deaths officially
Interpretation
Epidemiology And Surveillance Interpretation
From an epidemiology and surveillance perspective, the 2009 H1N1 swine flu spread rapidly and was closely tracked worldwide as WHO confirmed 27,737 cases across 74 countries with 141 deaths by June 19, 2009, after the United States reported 60.8 million symptomatic cases by April and Mexico logged 132 deaths by April 26.
03 · Category
Prevention And Vaccination20 stats
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Over 90 million doses of swine flu vaccine were administered in the US by February 2010
02
The swine flu vaccine efficacy was 68% against hospitalization in children
03
Single-dose swine flu vaccine provided 76% protection in adults 18-64 years
04
Adjuvanted swine flu vaccine had 84% efficacy in adults over 65
05
Pregnant women receiving inactivated swine flu vaccine had 50% reduced hospitalization risk
06
Two doses of swine flu vaccine were needed for children 6 months-9 years for full immunity
07
Vaccine coverage reached 40.5% in US healthcare workers for swine flu
08
Live attenuated nasal spray swine flu vaccine was 54% effective in children
09
Global swine flu vaccine production reached 4.4 billion doses capacity by 2010
10
UK vaccinated 30% of population against swine flu by March 2010
11
Pandemic swine flu vaccines contained 15μg HA per strain
12
Cross-protection from seasonal flu vaccine was minimal (19%) against swine flu
13
Vaccination prevented an estimated 1,100 pediatric hospitalizations per million doses
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Adverse events post-swine flu vaccine were similar to seasonal flu vaccine rates
15
High-risk groups prioritized for swine flu vaccine included 159 million worldwide
16
Brazil distributed 80 million swine flu vaccine doses in 2010 campaign
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Vaccine effectiveness against swine flu ICU admission was 79% in adults
18
Children under 2 had 92% seroconversion rate after two swine flu vaccine doses
19
Oseltamivir prophylaxis prevented 89% of swine flu cases in exposed contacts
20
Zanamivir was 96% effective as post-exposure prophylaxis for swine flu
Interpretation
Prevention And Vaccination Interpretation
In the Prevention And Vaccination category, swine flu immunization rolled out at massive scale with over 90 million doses in the US by February 2010 while delivering consistent protection across groups, ranging from 50% reduced hospitalization in pregnant women to 84% efficacy in adults over 65 with adjuvanted vaccine.
04 · Category
Transmission And Outbreaks20 stats
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Swine flu primarily spread via respiratory droplets from coughing/sneezing
02
One infected person could spread swine flu to 1.4-1.6 others (R0)
03
Household secondary attack rate for swine flu was 9.5%
04
Asymptomatic swine flu transmission accounted for 13-55% of cases
05
School closures reduced swine flu transmission by 20-30% in affected communities
06
Public transit use increased swine flu risk by 3.5 times in Hong Kong study
07
Nosocomial (hospital-acquired) swine flu was 11% of healthcare worker infections
08
International air travel seeded swine flu in 24 countries by May 2009
09
Pig-to-human transmission of swine flu was documented in 12 US cases by 2011
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Face masks reduced swine flu infection risk by 80% in household contacts
11
Hand hygiene compliance >60% lowered swine flu spread in schools by 16-50%
12
Mexico City outbreak peaked with 1,100 cases/week in April 2009
13
New York City swine flu outbreak had 865 cases by May 2009
14
UK swine flu wave peaked at 110,000 cases/week in July 2009
15
Contact tracing identified 70% of swine flu secondary cases in Australia
16
Fomites (surfaces) contributed <1% to swine flu transmission
17
Viral shedding in swine flu peaked day 1 of symptoms, lasting 5-7 days
18
Children shed swine flu virus 10-fold higher titers than adults
19
Quarantine of contacts reduced swine flu clusters by 50% in simulations
20
Social distancing measures cut peak swine flu incidence by 92% in models
Interpretation
Transmission And Outbreaks Interpretation
Swine flu spread efficiently through respiratory droplets with an R0 of about 1.4 to 1.6 and a 9.5% household secondary attack rate, while asymptomatic transmission covering 13 to 55% of cases showed why outbreaks could grow even before symptoms appeared.
Reference
Cite This Report
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APA
Leah Kessler. (2026, February 13). Swine Flu Statistics. Gitnux. https://gitnux.org/swine-flu-statistics
MLA
Leah Kessler. "Swine Flu Statistics." Gitnux, 13 Feb 2026, https://gitnux.org/swine-flu-statistics.
Chicago
Leah Kessler. 2026. "Swine Flu Statistics." Gitnux. https://gitnux.org/swine-flu-statistics.
Sources & references
21 datasets cited across this report · attribution is report-level