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DEFINING PANDEMIC
Dr Wan Noraini Wan Mohamed NoorHead of Surveillance Sector
Disease Control Division, MOH Malaysia3 May 2018
The Outline:
• Natural history and spectrum of disease
• Chain of infection
• Short quiz: What is the vocabulary?
• The epidemic & pandemic of the 21st century
• Why we’re at more risk than ever of a global pandemic?
• Pathways to a influenza pandemic
• The historical context of pandemic influenza
• Let’s watch a video clip …..
Natural History & Spectrum of Disease
• The spectrum of disease– The process may result in illness that ranges from mild to severe or fatal– In some people, the process may never progress to clinically apparent
illness (asymptomatic)
• Depending upon the infectivity, pathogenicity & virulence of the infectious agents
• Carrier – individual with asymptomatic infection but able to transmit the infection to others
Natural History of Disease Timeline – in the absence of treatment
Incubation period for infectious diseases & latency period for NCDs – varying from minutes to decades
Infectivity refers to the proportion of exposed persons who become infected. Pathogenicity
refers to the proportion of infected individuals who develop clinically apparent disease. Virulence
refers to the proportion of clinically apparent cases that are severe or fatal.
Chain of InfectionTransmission occurs when the agent leaves its reservoir or host (animal, human, environment) through a portal of exit, is conveyed by some mode of transmission (direct / indirect) and enters through an appropriate portal of entry to infect a susceptible host
Therefore, public health interventions are directed at:
▪ Controlling or eliminating agent at source of transmission
▪ Protecting portals of entry
▪ Increasing host’s defences
QUIZ: WHAT IS THE VOCABULARY?“Dem” is used for words relating to people and “Zoo” is used for words relating to animals.
QUESTION: Which of these words (A-F) do you think best fits the given description (1-6)?
A. Endemic 1. Literally means ‘upon people’, as a disease rapidly spread among people
B. Epidemic 2. Literally means ‘upon animals’, as a disease rapidly spread among animals
C. Epizootic 3. Disease that persists in a reservoir of an animal host, but can be transmitted from animals to humans
D. Pandemic 4. Literally means ‘in people’. This word has come to mean anything that normally resides in or is native to a population or region
E. Panzootic 5. Literally means ‘all people’, as disease rapidly spread to all people over a large region
F. Zoonosis 6. Literally means ‘all animals’, as disease rapidly spread to all animals over a large region
WHAT IS THE VOCABULARY?The Answers
B. Epidemic 1. Literally means ‘upon people’, as a disease rapidly spread among people
C. Epizootic 2. Literally means ‘upon animals’, as a disease rapidly spread among animals
F. Zoonosis 3. Disease that persists in a reservoir of an animal host, but can be transmitted from animals to humans
A. Endemic 4. Literally means ‘in people’. This word has come to mean anything that normally resides in or is native to a population or region
D. Pandemic 5. Literally means ‘all people’, as disease rapidly spread to all people over a large region
E. Panzootic 6. Literally means ‘all animals’, as disease rapidly spread to all animals over a large region
The constant presence and/or usual prevalence of a disease or infectious agent in a population within a geographic area
A disease that occurs infrequently and irregularly
An increase, often sudden in the number of cases of a disease above what is normally expected in a population of a wider geographic area
An epidemic that has spread over several countries or continents, usually affecting a large number of people
Epidemic Disease Occurrence
• When does epidemic occurs?– When an agent and susceptible hosts are present in adequate
numbers– When the agent can effectively conveyed from a source to the
susceptible hosts
• More specifically, an epidemic may occur from:– A recent increase in amount or virulence of the agent– The recent introduction of the agent into a setting where it has not
been before – An enhanced mode of transmission so that more susceptible persons
are exposed– A change in the susceptibility of the host response to the agent,
and/or– Factors that increase host exposure or involve introduction through
new portals of entry
Severe Acute Respiratory Syndrome (SARS)
• Emerged in November 2002 in the southern Chinese province of Guangdong
• February 2003, WHO was notified by the Chinese officials about 305 cases of atypical pneumonia that had occurred in Guangdong Province
• July 2003: SARS was declared contained
– In total, it caused 8,096 cases and 774 deaths in 26 countries worldwide mainly owing to isolation and quarantine (WHO, 2003)
Spread of SARS from the Metropole Hotel in Hong Kong (as of 28 March 2003)
How SARS influence the global economy?
The Economic Impact of Selected Infectious Diseases
• Fear of SARS infection leads to a substantial decline in consumer demand, especially for travel and retail sales service
• The uncertain features of the disease reduce confidence in the future of the affected economies
• SARS undoubtedly increases the costs of disease prevention, especially in the most affected industries such as travel and retail sales service industries
Pandemic (H1N1) 2009
• February 2009: The first-laboratory confirmed cases of H1N1 influenza appeared in Mexico
• April 2009: The event prompted the first activation of provision under the IHR (2005) – declaration of a PHEIC
• It presented a public health emergency of uncertain scope, duration and effect
• September 2009: US FDA approved the influenza A(H1N1) 2009 monovalent vaccine
April ‘09
July ‘10
WHO Briefing Notes: Pandemic (H1N1) 2009
“…. The 2009 influenza pandemic has spread internationally with unprecedented speed. In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less
than six weeks ….”
WHO , Geneva (16 July 2009)
Pandemic H1N1 2009– Estimated R0 (reproductive number): 1.1 to 1.8a
– Estimated CFR: 0.12%b
– Estimated attributable excess mortality worldwide: 100,000 –400,000c
– Age groups most affected: Children and young adults
a Fraser, C et al. Pandemic potential of a strain of Influenza A (H1N1): Early Findings. Science 2009, 324(5934):1557-1561b Van Kerkhove MD et al. H1N1pdm serology working group. Estimating age specific cumulative incidence for the 2009 influenza pandemic: a meta-analysis of A(H1N1)pdm09 serological studies from 19 countries. Influenza and Other Respiratory Viruses, 2013, Jan 21. doi: 10.1111/irv.12074
c Dawood FS et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza a H1N1 virus circulation: a modelling study. Lancet Infectious Diseases, 2012,12(9):687–695.
Ebola Epidemic in West Africa (2014)
• West Africa in general is characterized by exceptional population mobility across porous borders, driven to large extent by poverty
• December 2013: It began with a fatal infection of 18 month-old boy in Guinea, possibly from bat
• 8 August 2014: WHO declared that the conditions for a Public Health Emergency of International Concern (PHEIC) have been met by the Ebola Epidemic in West Africa
• In total, it killed 11,310 and infected more than 28,616
9th Meeting Of The IHR Emergency Committee
(26 March 2016): Declaration of PHEIC* status
termination by WHO
PHEIC*: Public Health Emergency of International Concern
How Does This Compare To Past Outbreaks?
Source: www.nytimes.com (data from WHO; as of 5 November 2014)
The continuing Ebola outbreak in West Africa has infected eight times the
number of people than all previous outbreaks combined.
Comparison of Previous Ebola Outbreaks to the 2014 West African Ebola Epidemic
Seven Reasons We're At More Risk Than Ever Of A Global Pandemic
Source: Meera Senthilingam, 10 April 2017, CNN (http://edition.cnn.com/2017/04/03/health/pandemic-risk-virus-bacteria/index.html)
1. Growing populations and urbanization
The United Nations predicting 66% of the global population will live in urban areas by 2050.
More people in cities can "put a strain on sanitation," said Dr. David Heymann
Seven Reasons We're At More Risk Than Ever Of A Global Pandemic (cont.)
Source: Meera Senthilingam, 10 April 2017, CNN (http://edition.cnn.com/2017/04/03/health/pandemic-risk-virus-bacteria/index.html)
2. Encroaching into new environments– Expanding populations encroach into previously uninhabited
territories, such as forests– With new territories comes contact with new animals and
inevitably, new infections
3. Climate change– Resulting in greater numbers of heat waves and flooding
events, bringing more opportunity for waterborne diseases such as cholera and for disease vectors such as mosquitoes in new regions
– Between 2030 and 2050, climate change is projected to cause about 250,000 additional deaths per year from heat stress, malnutrition and the spread of infectious diseases like malaria, according to the WHO
Seven Reasons We're At More Risk Than Ever Of A Global Pandemic (cont.)
Source: Meera Senthilingam, 10 April 2017, CNN (http://edition.cnn.com/2017/04/03/health/pandemic-risk-virus-bacteria/index.html)
4. Global travel– International tourist arrivals reached a record of almost 1.2
billion in 2015, according to the UN World Tourism Organization, 50 million more than 2014
– Global travel enables infections to spread before symptoms develop
– It's not just humans who spread disease through travel, it’s also trade
5. Civil conflict– Civil unrest can impair the ability
of a country's health system to handle an outbreak
Seven Reasons We're At More Risk Than Ever Of A Global Pandemic (cont.)
Source: Meera Senthilingam, 10 April 2017, CNN (http://edition.cnn.com/2017/04/03/health/pandemic-risk-virus-bacteria/index.html)
6. Fewer doctors and nurses in outbreak regions– Most have left for better prospects elsewhere– > 75 countries have fewer than 1 physician per 1,000
population and 50 countries have fewer than 1 nurse or midwife per 1,000 people
7. Faster information– Instant communication
everywhere raises the possibility that false rumours will spread during a crisis
– Fearful rumours may trigger panic, hindering response activities
How Do Influenza Pandemic
Happen?
Dr Wan Noraini Wan Mohamed NoorHead of Surveillance Sector
Disease Control Division, MOH Malaysia3 May 2018
Seasonal Influenza vs. Pandemic Influenza
Seasonal Influenza Pandemic Influenza
Caused by circulating influenza viruses; i.e. influenza A, B or C
Caused by a novel influenza virus –highly likely influenza A
Immunity acquired by previous infection or timely vaccination
Most people in the world have never been exposed and have no immunity
Influenza infection can be prevented by acquiring timely influenza vaccine
Vaccine will not be available initially. New vaccine production can take as long as 3-6 months
Characterized by severe disease and excess deaths at the extremes of the lifespan, i.e. the very young and the elderly
Characterized by severe disease in non-traditional age-groups, namely young adults
Taking it From the Perspective of Seasonal Influenza….
INFECTED~5%-20%
(1.5 – 6.0 million)
SYMPTOMATIC~50%
(0.75-3.0 million)
Malaysia Population ~30 million
SEEK CARE
TREAT @ HOME
TREAT @ OPD HOSPITALIZED
DEATH
RECOVERED
Influenza: The Likely Candidate to Cause a Pandemic
• Easily transmitted person-to-person, especially with today’s global traffic
• Short incubation period → spread quickly
• Transmitted by infected but asymptomatic individual
• Symptoms are non-specific and wide ranging
• Cause death in all age groups
• People at risk may have no prior immunity – infectious worldwide
Pandemic Influenza• Highly pathogenic avian influenza A viruses could be a
source of the next pandemic influenza virus strain
• Requirement for an influenza pandemic:
– A new influenza A subtype emerges that can infect humans; AND
– Ability to cause serious illness; AND
– Ability to spread easily from human-to-human
Influenza Virus Change: ‘Drift’ And ‘Shift’
ANTIGENIC DRIFT ANTIGENIC SHIFT
THE PROCESS • Small changes that happen continually over time
• MINOR change in the HA and NA proteins
• Antibodies previously produced towards the influenza viruses (via infection or vaccination with earlier strains) may not be protective against viruses circulating in later years
• Abrupt, major change in the influenza A viruses
• MAJOR change in the HA and NA proteins
• When shift happens, most people have little or no protection against the new virus
• Can happens in 3 ways
FREQUENCY Happens all the time Happens only occasionally
OUTCOMES • Seasonal epidemics in populations• Multiple infections over a person’s
lifetime• Necessitate frequent updating of
influenza vaccine components to ensure that the vaccine is matched to circulating viruses
Novel virus → Pandemic (possible)
REMARK:• Influenza type A viruses: BOTH
antigenic drift & shift• Influenza type B viruses: Antigenic
drift ONLY
Influenza Pandemics Historically
• Unpredictable but recurring events that can have significant global consequences
• Since 16th century, influenza pandemics have been described at intervals ranging between 10 and 50 years with varying severity and impact
Recorded human pandemic influenza since 1889 (early sub-types inferred)
Source: European Centre for Disease Prevention and Control (ECDC) 2009
Reproduced and adapted (2009) with permission of Dr. Masato Tashiro, Director, Centre for Influenza Virus Research, National Institute of Infectious Diseases (NIID), Japan
Spanish Flu (1918-1920)
• An estimated 1/3 of the world’s population (or ≈ 500 million persons) were infected & had clinically apparent illnesses
• Case fatality rates were > 2.5%
• Total deaths were estimated at ≈ 50 million
• Generally viewed to have had 3 distinct waves
Three pandemic waves: weekly combined influenza and
pneumonia mortality, United Kingdom, 1918–1919
Spanish Flu (1918-1920)• Causing disproportionate burden among young people,
particularly previously healthy individuals 18-40 years of age– It may be related to the role of infection in turning the immune
system against itself. Consequently, those with the most robust immune systems may have been at greatest risk
– It may also have been due to prior exposure to a genetically similar strain among older age groups
• Reviewed evidence suggested that the origin of the 1st wave of Spanish Flu Pandemic was an outbreak in China that was misidentified as pneumonic plague– It then would have spread across the globe through the Chinese
Labour Corps (CLC), a group that, from 1916 to the end of the First World War, sent over 100,000 labourers to Europe to support the Allied war effort
• In 1918, effective vaccines and antibiotics to prevent influenza and treat secondary bacterial pneumonia were unavailable
‘Emergency Hospital’ During Spanish Flu Pandemic 1918(Funston Camp, Kansas, USA)
In 1918, children would skip rope to this rhyme ….
Pandemic (H1N1) 2009: Major Timeline
• February 2009: The first-laboratory confirmed cases of H1N1 influenza appeared in Mexico
• April 2009: The event prompted the first activation of provision under the IHR (2005) – declaration of a PHEIC
• 11 June 2009: WHO declared a global influenza pandemic
• September 2009: US FDA approved the influenza A(H1N1) 2009 monovalent vaccine
• August 2010: WHO declared the pandemic officially over
April ‘09
July ‘10
Pandemic (H1N1) 2009: Key Facts• Estimated Ro (reproductive number): 1.1 to 1.8a
• Estimated CFR: 0.12%b
• Estimated attributable excess mortality worldwide: 100,000 – 400,000c
• Age groups most affected: Children and young adults
• Exhibited wave behaviour, with wave timing varying geographically
a Fraser, C et al. Pandemic potential of a strain of Influenza A (H1N1): Early Findings. Science 2009, 324(5934):1557-1561
b Van Kerkhove MD et al. H1N1pdm serology working group. Estimating age specific cumulative incidence for the 2009 influenza pandemic: a meta-analysis of A(H1N1)pdm09 serological studies from 19 countries. Influenza and Other Respiratory Viruses, 2013, Jan 21. doi: 10.1111/irv.12074
c Dawood FS et al. Estimated global mortality associated with the first 12 months of 2009 pandemic influenza a H1N1 virus circulation: a modelling study. Lancet Infectious Diseases, 2012, 12(9):687–695.
WHO Briefing Notes: Pandemic (H1N1) 2009
“…. The 2009 influenza pandemic has spread internationally with unprecedented speed. In past pandemics, influenza viruses have needed more than six months to spread as widely as the new H1N1 virus has spread in less
than six weeks ….”
WHO , Geneva (16 July 2009)
WHO: Pandemic Influenza Phases (2009)
“When I was a kid, the disaster we worried about most was a nuclear war.
But today, if anything kills over 10 million people in the next few decades, it’s most likely to be a highly infectious virus, rather than a war.
Not missiles,But microbes.”
Bill Gates via TED Talk(March 2015)
