Pandemic preparedness: What can epidemiological modelling offer policy?

1
Pandemic preparednessWhat can epidemiological
modelling offer policy?

• Nim Arinaminpathy
• Department of Zoology
• University of Oxford

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Talk plan

• Influenza a background
• From today to emergence of a novel influenza
  virus
• Antiviral drugs for control of pandemic influenza

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Influenza

• RNA virus
• Clinical manifestations
• Headache, sore throat, chills, fever,
• myalgia, anorexia, malaise
• Transmission
• By contact with respiratory droplets,
• generated by coughing or sneezing
• Infectiousness
• can start a day before symptoms and continue for
  3 5 days after symptoms developing in adults

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The seasonal influenza burden

• Disease
• 5 15 of population affected with upper
  respiratory tract infections in annual flu
  season
• Estimated 3-4,000 annual deaths in UK caused by
  influenza infection (mainly elderly and
  immunocompromised)
• The Economy
• Europe flu accounts for 10 of sick leave
• Costs US estimated 90bn a year

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Influenza family tree
Orthomyxoviridae

Influenza
From http//www.abc.net.au/health
A
B
C
Type

H1N1
Subtype
H3N2
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Pandemic and seasonal influenza
Taken from www.en.influenza.pl
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Social and economic disruption
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Social and economic disruption
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H5N1 Future pandemic?

• Wild bird reservoir ? Poultry ? Humans
• Transmitted from bird to human by inhaling dried
  aerosolised faeces
• First major outbreak in 1997, Hong Kong
• Resurgence in 2003 has seen virus established in
  poultry in South-East Asia
• So far human-to-human spread is non-existent or
  very limited
• 387 human cases, 245 deaths to date
• Wide geographical spread, from S.E.Asia (inc.
  Indonesia, Viet Nam) to Africa (Nigeria, Egypt)
• However, H7N7 and N9N2 are also pandemic
  candidates

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Evolution and emergence of pandemic influenza

• Each human case is an opportunity for an avian
  virus to adapt for human transmission

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Antiviral drugs for pandemic control

• No vaccine for at least first 6 months
• Oseltamivir (Tamiflu) is main antiviral drug of
  choice
• UK stockpile
• Currently enough for 25 of population
• Drugs intended mainly for treatment, not
  prophylaxis
• For all clinical cases
• How best to minimise epidemic size and impact
  with a limited stockpile?

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A simple compartmental model
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A simple compartmental model
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1957 Asian Flu pandemic
30/11/57
22/02/58
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1957 Asian Flu pandemic
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1957 Asian Flu pandemic
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1957 Asian Flu pandemic
CFR 0.16 R0 1.65
25 stockpile exhausted
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How many drugs are needed?
Secondary effect of mass antiviral treatment is
to reduce the spread of infection in the
community Its strength depends on drug
efficacy and disease transmissibility
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Antiviral programmes

• By shortening infectious period and reducing
  infectiousness, antiviral drugs can influence the
  course of infection
• Broadening and delaying epidemic peak
• Reducing numbers of cases
• If there is a risk-group for whom the drug has
  little protective effect, the stockpile is better
  deployed in the general population.
• Priority shifts to protection from infection
  rather than from illness.

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The social element

• Potential wastage of drugs on the worried well
• Personal stockpiles
• Non-compliance with treatment regime may lead to
  drug resistance
• Pressing ethical questions, eg distributive
  justice

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Conclusions

• Mathematical models can offer valuable insights
  into disease control
• Transmission dynamics are often fundamental to
  epidemic outcomes and effects of interventions
• sometimes offering counterintuitive results!
• However models always entail simplifications,
  often about human behaviour (important factors)
• Effective pandemic preparedness could involve a
  synergy between such models and the social
  sciences