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Miriam Nu ño Harvard School of Public Health, USA Gerardo Chowell Los Alamos National Laboratory, USA Abba Gumel

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Assessing Basic Control Measures, Antivirals, and Vaccine in Curtailing Pandemic Influenza: Scenarios for the US, UK and South Africa. Miriam Nu ño Harvard School of Public Health, USA Gerardo Chowell Los Alamos National Laboratory, USA Abba Gumel

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slide1

Assessing Basic Control Measures, Antivirals,

and Vaccine in Curtailing Pandemic Influenza:

Scenarios for the US, UK and South Africa

Miriam Nuño

Harvard School of Public Health, USA

Gerardo Chowell

Los Alamos National Laboratory, USA

Abba Gumel

University of Manitoba, Canada

AIMS/DIMACS/SACEMA Workshop

slide2

Outline

  • Motivation
  • Control Interventions
  • Model and Assumptions
  • Reproduction Numbers
  • Results: US, UK, South Africa Scenarios
  • Current Pandemic Preparedness Plans
slide3

Motivation

  • Assess the role of several interventions in reducing the burden of a potential flu pandemic
  • Determine the “optimal” flu pandemic preparedness plan?
  • Evaluate current preparedness plans for the US, UK and South Africa
slide4

Antivirals

  • Adjunct to flu vaccine for control and prevention
  • Adamantanes: amantadine (A) and rimantadine (R); flu A
  • NA inhibitors: zanamivir (Z) and oseltamivir (O); flu A and B
  • Antivirals differ in side effects, route of administration, approved ages, dosages and costs
  • Used for treatment or prophylaxis
slide5

Antiviral Treatment

  • Adamantanes can reduce duration of uncomplicated flu A by ~1 day

(if administered within 2 days of illness onset )

  • NA inhibitors provide similar reduction against both flu A and B
  • Recommended duration of treatment with NA inhibitors is 5 days
  • Therapy with adamantanes should be discontinued when clinically possible

to reduce resistance (3-5 days of treatment or within 24-48 hours of symptoms disappearance)

slide6

Antiviral Chemoprophylaxis

  • Adamantanes preventive effectiveness to flu A approximately 70%-90%
  • Only Oseltamivir has been approved for prophylaxis (80% effective)
  • Implementation involves: cost, compliance and potential side effects
  • Maximum-effectiveness approach: taken each day for the duration of flu activity
  • Cost-effective approach : Adamantanes taken during period of peak flu activity
  • Doses vary according to age, risk groups, and other factors
slide7

Seasonal Flu Vaccine

  • Inactivated (killed-virus) vaccine approved for people older than

6 months; including healthy and chronically ill

  • Nasal-spray (live-weakened) vaccine approved for healthy people 5-49 years (excluding pregnant women)
  • Trivalent dose with 2 type A (H3N2, H1N1) and one type B virus
  • Vaccine updated each year
  • Protecting antibodies develop ~ 2 weeks following vaccination
  • Who should get vaccinated:

(1) people at high-risk of complications

(2) people caring for high-risk groups

  • High-risk groups include:

(1) children 6-59 months, (2) pregnant women, (3) elderly ages 50+

(4) chronically ill of any age, (5) immune compromised

slide8

Other Public Health Interventions

  • Isolation and Quarantine
  • Face masks
  • Behavioral changes
slide10

Basic Reproduction Number

Average number of new cases generated by an

infectious individual during its period of infectiousness

in a completely susceptible population (no interventions)

slide11

Intervention Reproduction Numbers

Control Reproduction Number:

Vaccination Reproduction Number:

Antiviral Reproduction Number:

Combined Reproduction Number:

slide13

United States Scenario

Population Demographics

Population Size: 298,444,215

High risk: 6 x 107(~ 20%)

Low risk: 2.4 x 108 (~ 80%)

Baseline Predictions

R0: ~ 1.4-2.4

Case Fatality Rate: 0.37%-2.5%

Clinical Attack Rate: 25%-50%

slide14

Baseline Scenarios

(no interventions)

slide22

R

R

0

0

Summarized Results: US Scenario

No Interventions

20% Basic Control Measures

10%

Attack Rate

1.6 1.9 2.1 2.4

1.6 1.9 2.1 2.4

Infections

Deaths

Hospitalizations

slide23

United Kingdom Scenario

Population Demographics

Population Size: 60,609,153

High risk: 6.1 x 106 (~ 10%)

Low risk: 54.9 x 106 (~ 90%)

Baseline Predictions

R0: ~ 1.28-2.0

Case Fatality Rate: 0.3%-3.0%

Clinical Attack Rate: 30%-50%

slide24

Baseline Scenarios

(no interventions)

slide25

South Africa Scenario

Population Demographics

Population Size: 44,187,637

High risk: (~ 25%-50%)

Low risk: (~ 50%-75%)

Baseline Predictions*

R0: ~ 1.6-2.4

Case Fatality Rate: 4%-4.5%

Clinical Attack Rate: 11%-44%

slide26

Baseline Scenarios

(no interventions)

slide28

R

R

0

0

Summarized Results: South Africa Scenario

No Interventions

20% Basic Control Measures

10%

Attack Rate

1.6 1.9 2.1 2.4

1.6 1.9 2.1 2.4

Infections

Deaths

Hospitalizations

slide29

Results

  • Optimal intervention strategy is country-specific
  • Antivirals are the best single intervention strategy
  • Therapeutic antivirals preferred over prophylaxis for countries

with limited resources

  • Vaccine is the next best single strategy intervention strategy
  • Basic control interventions reduce the burden of a pandemic,

however, a pandemic may be prevented if R0 =1.6

  • Combined intervention is by far themost effective strategy
slide30

Assessing Flu Pandemic Preparedness Plans:

US, UK and South Africa

Preparedness and Communication

Surveillance and Detection

Response and Containment

slide31

Preparedness Plans

Goal:

  • Minimize the burden of a flu pandemic

(morbidity and mortality)

  • Minimize social disruption

Approach:

  • Antivirals (prophylaxis and therapeutic)
  • Flu vaccination
  • Pneumococcal immunization of high-risk groups
  • Isolation, quarantine and travel restrictions
slide32

Current Preparedness Plans

United StatesUnited KingdomSouth Africa

Basic Control yesyesyes

Measures

Antivirals

Prophylaxis yesrestricted yes

Treatmentyesyes yes

Flu Vaccine yesyes yes

Pneumococcal noyes no

Immunization

slide33

Resources Available

US UKSouth Africa

Population298,444,21560,609,15344,187,637

(high risk) (6 x 107)(6.1 x 106)(11 x 106)

Life Expectancy (birth)77.85 years78.54 years42.72 years

HIV adult prevalence rate0.6% 0.2%21.5%

Interventions

Antivirals40M-75M 15M?

(25% population?)(25%)

Flu Vaccine83.1M-100M 14M ?

slide34

Closing Remarks

  • What can be learned from the discussed preparedness plans?
  • Is there a single optimal strategy to prepare for pandemic flu?
  • Hospital and community control measures can go a long way, particularly in developing countries with poor resources
  • Prophylaxis versus therapeutic us of antivirals!!
  • Complications in countries with high HIV and TB prevalence
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