0. David Liu Smallpox: Gone but not forgotten
Antiviral Treatment Is More Effective Than Smallpox Vaccination Upon Lethal Monkeypox Virus Infection
Stittelaar, et al.
Nature Feb 9;439(7077):745-8

1. History: Vaccination and Eradication
Variola Major
The first vaccine in history was developed for smallpox by Edward Jenner in 1796.
By the 1960s, smallpox was limited to developing countries—completely eradicated from the West. Vaccinia vaccine.
1967 WHO global vaccination campaign
Last natural case in 1977
In 1978, all known stocks were transferred to either the CDC in Atlanta or the VECTOR Institute in the USSR.

2. Possible: bioterrorism
Smallpox is:
Easily transmissible
High mortality rate
Disfiguring
Vaccination has stopped virgin population
Pox Americana
Hypothetical illicit sources.
Known weaponization of smallpox in the former Soviet Union
Flat-type smallpox: Mortality rate > 96%
Hemorrhagic-type smallpox: Mortality rate > 98%

3. CDC response plan Overall plan:
1) Identify and isolate smallpox cases to prevent further disease spread,
2) Identify, vaccinate, and monitor contacts of cases and household contacts of contacts, to prevent secondary cases.
Stance on post-exposure: “if [the vaccine is] administered within 3 days after exposure to smallpox virus, it may prevent disease, or decrease the severity of disease and risk of death.”
Newest version 3.0: The CDC Smallpox Response Plan and Guidelines were last updated on September 23, 2002.

4. Antiviral treatment: nucleotide analogues (De Clerq, 2004)
Acyclic nucleotide phosphonates

5. Research Question
What would be the efficacy of post-exposure vaccination versus antiviral treatment in the event of poxvirus re-emergence, e.g. a bioterrorist attack?
Proof of concept study

6. Overview of methods
Infect monkeys with a lethal respiratory dose of monkeypox virus
Why not smallpox?
Determine treatment efficacy in drug-treated, vaccinated, and control groups
Five parameters (independent variables): survival, O2 profile, lesions, viral load, immune response (antibodies/T-cells)
Measurements made on days 1, 3, 5, 7, 10, 13, 18, 21, 26
Throat swabs, plasma samples, O2 readings, observation

7. Setting up. Infection of monkeys with 107 pfu of MPXV
Segregation into experimental groups:
I : Control (n=17) (n=6)
II: Elstree-RIVM (vaccinia-virus vaccine) (n=6)
III: Cidofovir (5 doses): Days 1, 3, 7, 10, 13 (n=6)
IV: Cidofovir (6 doses): Days 1, 3, 5, 7, 10, 13 (n=6)
V: HPMPO-DAPy (5 doses) (n=4)
VI: HPMPO-DAPy (6 doses) (n=6)
Already proven that pre-exposure vaccination is effective against smallpox infection (Stittelaar 2005)
Drugs given in dosages of 5 mg kg-1
Monkeys in group III — VI were also given probenecid

8. Methods for Parameter 1: Survival
Kaplan-Meier Plot
Commonly used in epidemiological studies
Accounts for “lost” subjects
Depicts the probability of survival at time t
Approximate true survival curve
Plasma creatinine levels

9. Results for Parameter 1: Survival
Figure 1.

10. Methods for Parameter 2/3: Blood O2 levels and lesions
Complications of smallpox most commonly arise in the respiratory system, usually around day 8
Dyspnea/anorexia
Blood O2 levels measured using pulse oximeter
Lesions are an obvious sign of the severity of the virus

11. Results for Parameter 2/3: Blood O2 levels and lesions
Figure 2.

12. Methods for Parameter 4: Viral Load
Real-time PCR with monkey plasma/throat swabs for MXPV DNA (dsDNA virus)
Simultaneous amplification and quantification
Fluorescent nucleotides
HA gene primer
The golden standard of viral studies

13. Results for Parameter 4: Viral Load
Figure 3.

14. Methods for Parameter 5: Immune Response
ELISA with RK13 cells as a reference
MPXV- specific IgG Antibodies
Interferon-γ ELISPOT assay
MPXV-specific T-Cells
80% of peripheral blood is T-cells

15. Results for Parameter 5: Immune Response
Supplementary Figure 1.

16. Summary of Results Post-exposure vaccination not effective
Cidofovir and HPMPO-DAPy can protect macaques against MXPV when administered early
6 doses better than 5
HPMPO-DAPy performed better than Cidofovir
Drug treatment allows for development of antibody resistance

17. Possible Limitations Better smallpox vaccines
Possible toxicity (monkey 23)
Small sample sizes
Proof of concept
Monkey model

18. Implications
Need to rethink efficacy of post-exposure vaccination strategies
Integration of antiviral drugs into CDC emergency response plan

19. Future Research
In vitro experimentation with antiviral drugs in Variola Major
Combining vaccine and drug therapy
Changing dosage schedules

20. Debate Proposed destruction in 1986.
Destruction postponed to 1993, and has been a resurfacing issue ever since.
Last visitation was in 2011
Will be revisited again in 2014

21. References