The 2009-2010 A(H1N1v) pandemic

Situation report Europe and forward look to the autumnZsuzsanna Jakab, DirectorEuropean Centre for Disease Prevention and Control

Swedish Presidency Workshop, Jönköping, 2-3 July 2009

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Pandemics of influenza

H7

H5

H9*

1980

1997

Recorded new avian influenzas

1996 2002

1999

2003

1955 1965 1975 1985 1995 2005

H1N1

H2N2

1889Russianinfluenz

aH2N2

H2N2

1957Asian

influenzaH2N2

H3N2

1968Hong Konginfluenza

H3N2

H3N8

1900Old Hong

Kong influenza

H3N8

1918Spanishinfluenza

H1N1

1915 1925 1955 1965 1975 1985 1995 20051895 1905 2010 2015

2009Novel

influenzaH1N1v

Recorded human pandemic influenza(early sub-types inferred)

Reproduced and adapted (2009) with permission of Dr Masato Tashiro, Director, Center for Influenza Virus Research, National Institute of Infectious Diseases (NIID), Japan.

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H1N1

H1N1v

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Situation report Europe,as of 1 July 2009

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Cumulative distribution of confirmed cases of A(H1N1)v by day of reporting, as of 29 June 2009, log scale

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26/04/09 03/05/09 10/05/09 17/05/09 24/05/09 31/05/09 07/06/09 14/06/09 21/06/09 28/06/09

France

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Selected European countries

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The situation could be a lot worse for Europe! (Situation circa summer 2009) A pandemic strain emerging in the

Americas Immediate virus sharing so rapid

diagnostic and vaccines Based on A(H1N1)v currently not that

pathogenic Some seeming residual immunity in a

major large risk group No known pathogenicity markers Initially susceptible to oseltamivir Good data and information coming out of

North America Arriving in Europe in the summer Milder presentation initially

A pandemic emerging in SE Asia

Delayed virus sharing

Based on a more pathogenic strain, e.g. A(H5N1)

No residual immunity

Heightened pathogenicity

Inbuilt antiviral resistance

Minimal data until transmission reached Europe

Arriving in the late autumn or winter

Severe presentation immediately

Contrast with what might have happened — and might still happen!

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But no room for complacency (Situation and information: late May 2009) Pandemics take some time to get going (1918 and

1968). Some pandemic viruses have ‘turned nasty’ (1918

and 1968). Is the ‘mildness’ and the lack of older patients

because older people are resistant or because the virus is not transmitting much among them?

There will be victims and deaths — as in the US — in risk groups (young children, pregnant women and especially people with other underlying illnesses).

As the virus spreads south, will it exchange genes with seasonal viruses that are resistant: A(H1N1)-H247Y, more pathogenic A(H3N2), or even highly pathogenic A(H5N1)?

An inappropriate and excessive response to the pandemic could be worse than the pandemic itself.

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So far in Europe

A mild disease in most people Easy to miss in surveillance Some severely ill and starting to see deaths – mostly

in people with other underlying conditions Few cases in people over 60 years Spreading efficiently Out-breaks in schools (or easier to see in schools?)

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Initial experience in North America 2009 – the default position

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Emerging themes in North America, early June 2009 (1) Early epidemic about 1 million infected ( = 0.3% of

population) – compared to minimum 25% expected attack rate Infection rate for probable and confirmed cases highest in

5−24 year age group. Hospitalisation rate highest in 0−4 year age group, followed

by 5−24 year age group. – Pregnant women, some of whom have delivered prematurely,

have received particular attention but data inadequate to determine if they are at greater risk from H1N1v than from seasonal influenza as already established.

Most deaths in 25−64 year age group; most with known risks for severe disease.

– Morbid obesity a risk but may be indicator for pulmonary risk. Adults, especially 60 years and old, may have some degree of

preexisting cross-reactive antibody to the novel H1N1 flu virus.

Transmission persisting in several regions of the U.S. Expected to run on throughout the summer and then

accelerate.

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Emerging themes in North America, end June 2009 (2) Containment impossible with multiple introductions and R0

1.4 to 1.6. Focus on counting laboratory-confirmed cases changing to

seasonal surveillance methods.– Outpatient influenza-like illness, virological surveillance

(including susceptibility), pneumonia and influenza mortality, pediatric mortality and geographic spread.

Serological experiments and epidemiology suggest 2008–2009 seasonal A(H1N1) vaccine does not provide protection.

Preparing for the autumn and winter when virus is expected to return.

Communication difficulty — a pandemic may be 'mild' yet cause deaths

– 25% of U.S. stockpile deployed to states (includes medication and equipment)

– determining who to give vaccine, if and when to begin using vaccine

– school closures being analysed to determine effectiveness

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Forward look for Europe

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Idealised curve for planningReality is never so smooth and simple

Single wave profile showing proportion of new clinical cases, consultations, hospitalisations or deaths by week. Based on London, 2nd wave 1918.

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25%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Week

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Source: Department of Health, UK

Initiation Acceleration Peak Declining

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One possible European scenario — summer and autumn 2009

In reality, the initiation phase can be prolonged, especially in the summer months. What cannot be determined is when acceleration takes place.

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Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

Month

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Initiation Acceleration Peak Declining

Apr

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One possible European scenario — summer 2009

July

August

October

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August

September

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Some of the 'known unknowns' inthe 20th century pandemics Three pandemics (1918, 1957, 1968) Each quite different in shape and

waves Some differences in effective

reproductive number Different groups affected Different levels of severity including

case fatality ratio Imply different approaches to

mitigation

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1918/1919 pandemic: A(H1N1) influenza deaths, England and Wales

1918/19: ‘Influenza deaths’, England and Wales. The pandemic affected young adults, the very young and older age groups.

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1918 1919Week no. and year

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Ro = 2-3 (US) Mills, Robins, Lipsitch (Nature 2004)Ro = 1.5-2 (UK) Gani et al (EID 2005)Ro = 1.5-1.8 (UK) Hall et al (Epidemiol. Infect. 2006)Ro = 1.5-3.7 (Geneva) Chowell et al (Vaccine 2006)

Courtesy of the Health Protection Agency, UK

Transmissibility: estimated Basic Reproductive Number (Ro)

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1957/1958 pandemic: A(H2N2) — especially transmitted among children

Ro = 1.8 (UK) Vynnycky, Edmunds (Epidemiol. Infect.2007)Ro = 1.65 (UK) Gani et al (EID 2005)Ro = 1.5 (UK) Hall et al (Epidemiol. Infect. 2006)Ro = 1.68 Longini et al (Am J Epidem 2004)

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July August September October November December January February

Week number and month during the winter of 1957/58

Reco

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influenza

1957/58: ‘Influenza deaths’, England and Wales

Courtesy of the Health Protection Agency, UK

Transmissibility: estimated Basic Reproductive Number (Ro)

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So what can we expect in our countries?

Some features from the ECDC risk assessment

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It will vary from place to place – and local can be more intense than national

In reality, larger countries can experience a series of shorter but steeper local epidemics.

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0%

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1918 NewYork State

1918Leicester

1918Warringtonand Wigan

1957 SELondon

1968Kansas City

clin

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Numbers affected in seasonal influenza epidemics and pandemics (overall clinical attack rate in previous pandemics)

Seasonalinfluenza

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Seasonal influenza compared to pandemic — proportions of types of cases

Asymptomatic

Clinicalsymptoms

Deaths

Requiring hospitalisation

Seasonal influenza Pandemic

Asymptomatic

ClinicalsymptomsDeaths

Requiring hospitalisation

There will be pressure on the primary and secondary health services – especially paediatric and intensive care.

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Good news

Older people spared Sensitive to antivirals No pathogenicity markers

But influenza is promiscuous – will it pick up any ‘bad’ genes on its winter holiday in the south – primary oseltamivir resistance from seasonal flu or even pathogenicity genes from ‘bird flu’ A(H5N1).

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Measuring the severity of a pandemic

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There is an expectation that pandemics should be graded by severity But there are difficulties: Severity varies from country to country. It can change over time. Some relevant information is not available initially. Key health information includes medical and

scientific information:– epidemiological, clinical and virological

characteristics There are also social and societal aspects:

– vulnerability of populations;– capacity for response;– available health care;– communication; and– the level of advance planning.

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WHO: A(H1N1)v — a ‘moderate’ pandemic

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What is meant by 'moderate' and 'severe'? Not a simple scale What most people experience. Attributable risks? For most

people it’s a mild self-limiting disease. Death ratio. Expectation of an infected person dying (the Case

Fatality Ratio): < 0.5% of reported cases. Hospitalisation rate: Rates for children aged 0-23 months, 2-4

years, and 5-17 years were 1.1, 0.3, and 0.3 per 10,000, respectively. Rates for adults aged 18-49 years, 50-64 years, and >= 65 years were 0.1, 0.1, and 0.2 per 10,000, respectively.1

Pathogenicity markers and animal studies. No markers but ferret data indicate somewhat more severe than seasonal flu.

Number of people falling ill with respiratory illnesses at one time — 'winter pressures'. Pressure on the health services' ability to deal with these — very related to preparedness and robustness. Watch UK, Australia, Argentina, Chile, New Zealand.

Critical service functioning. Peak prevalence of people off ill or caring for others. Watch Australia, Chile, New Zealand.

1 http://www.cdc.gov/flu/weekly/: 2008-2009 Influenza Season Week 24 ending June 20, 2009

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What is meant by 'moderate' and 'severe'? Not a simple scale Certain groups spared: older people. Certain individual dying unexpectedly, e.g.

children, pregnant women, young healthy adults. Public and media perception: low perception of

risk at present

Conclusion Not easy to come up with a single measure of

severity. May be better to state or agree what

interventions/countermeasures are useful and justifiable (and what are not).

http://www.who.int/csr/disease/swineflu/assess/disease_swineflu_assess_20090511/en/index.html and http://www.who.int/wer/2009/wer8422.pdf

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Surveillance in a pandemic – future look

This will be crucial to detect– Changes in the behaviour of the virus– Discover who is really at risk

Will have to stop asking for numbers very soon Reliance on sentinel work – the previous EISS system

through TESSy Reporting of severe disease especially important for

informing the antiviral and vaccine priorities Special workshop 14-15 July in Stockholm

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Conclusions

This pandemic will run through the rest of 2009-2010.

The first wave will probably start earlier than we might like.

While this looks like a ‘moderate’ pandemic - there will be surprises.

Europe is better prepared than many other regions and a lot better prepared than we were in 2005.

Final preparations will be very worthwhile. ECDC will be there to work with the

Commission, EMEA and WHO to give every support to Member States.

Thank you!