Presentation by Dr. Joacim Rocklöv during the ESCAIDE 2016 plenary session on Zika on 30 November 2016 in Stockholm, Sweden

1. What scenarios for the epidemiological
pattern of Zika infection in the future?
Joacim Rocklöv
Umeå Centre for Global Health Research
Epidemiology and Global Health
Umeå University, Sweden

2. Virus, Vector & Susceptible
people
The Zika Epidemic
Microcephaly & GBS
?
T
I
M
E

3. 0
2
4
6
8
10
12
2 3 4 5 6 7 8 9 10 11
Months (Year 2016)
Numberofarticles
Studies of relevance for Zika preparedness
In preparation
Sudre B et al.

4. Type of studies
• Descriptive epidemiological
• R0 studies
• Ecological niche modeling
• Vector competence
• Transmission parameters
• Travel
• Risk assessments
• Role of sexual transmission
• Cost-effectiveness
• Long-term scenarios
More
Less

5. Ecological niche modeling:
• Estimating zones of potential further expansion
• Contrasting results between studies
• Larger extent estimates 2.17 billion populations
at risk
• Zika case based study identifies a narrower risk
region and concludes Zika is driven by a more
typical tropical climate compared to Aedes &
dengue based assessments. Limited database.
• Weakness: omitting time sensitivity of event,
e.g. el Nino
More
Less
Messina JP, Kraemer MU, Brady OJ, Pigott DM, Shearer FM, Weiss DJ, et al. Mapping global environmental suitability for Zika virus. Elife. 2016;5:e15272.
Carlson C, Dougherty E, Getz W. An ecological assessment of the pandemic threat of Zika virus. bioRxiv [Internet]. 2016. Available from: http://dx.doi.org/10.1101/040386.

6. Aedes susceptibility to ZIKV
• Appears low, especially for Ae. Albopictus
• Spatially variable
• Parameterized lower competence contrast to
findings in epidemiological data, and to prior
findings on Asian vectors and virus
• Conflicting indications of the role of sexual
transmission potentially confounding these
associations
Chouin-Carneiro T. V-RA, Vazeille M., Yebakima A., Girod R., Goindin R., Dupont-Rouzeyrol M., Lourenço-de-Oliveira R., Failloux A.B. Differential Susceptibilities of
Aedes aegypti and Aedes albopictus from the Americas to Zika Virus. PLoS neglected tropical diseases. 2016;10(3).
Di Luca M, Severini F, Toma L, Boccolini D, Romi R, Remoli ME, et al. Experimental studies of susceptibility of Italian Aedes albopictus to Zika virus. Euro
surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin. 2016;21(18).

7. Travelling & risk modeling
• Estimating number of travellers from catchment
areas (polygons) around airports in Aedes
suitable regions of Brazil to airports outside this
region
• Usually not capturing level of epidemic intensity
at the time of travel rather suitability of
transmission (yes/no)
• Later studies use seasonality in epidemic region
and risk region by using dengue vectorial
capacity. Show seasonal risk for spread.
• Limitation: descriptive indexes, not integrated to
yield risk estimates
Bogoch, II, Brady OJ, Kraemer MU, German M, Creatore MI, Brent S, et al. Potential for Zika virus introduction and transmission in resource-limited countries in Africa
and the Asia-Pacific region: a modelling study. Lancet Infect Dis. 2016;16(11):1237-45.
Bogoch, II, Brady OJ, Kraemer MU, German M, Creatore MI, Kulkarni MA, et al. Anticipating the international spread of Zika virus from Brazil. Lancet. 2016;387(10016):335-6.
Rocklov J, Quam MB, Sudre B, German M, Kraemer MU, Brady O, et al. Assessing Seasonal Risks for the Introduction and Mosquito-borne Spread of Zika Virus in Europe.
EBioMedicine. 2016;9:250-6.

8. - Vad är Zika
- Hur sprids viruset
- Vad är symptomen
- Vad vet vi om riskerna?
- Hur epidemiskt är det, och hur vet man det?
- Risker för spridning till nya områden
- Fortsatt spridning i Latin Amerika
- Risker i Europa
Rocklov, J., M. B. Quam, B. Sudre, M. German, M. U. Kraemer, O. Brady, Bogoch, II, J. Liu-Helmersson, A. Wilder-Smith, J. C. Semenza, M. Ong, K. K. Aaslav and K. Khan (2016).
"Assessing Seasonal Risks for the Introduction and Mosquito-borne Spread of Zika Virus in Europe." EBioMedicine 9: 250-256.
Di Luca M, Severini F, Toma L, Boccolini D, Romi R, Remoli ME, et al. Experimental studies of susceptibility of Italian Aedes albopictus to Zika virus. Euro
surveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin. 2016;21(18).
High risk scenario of
albopictus susceptibility to
ZIKV. European studies
suggests a lower vector
competence.

9. Reproduction number:
• R0 estimates heterogeneous, approximately in
the range of 1-7
• Smaller confined areas higher R0
• Mixing of population, e.g. population mobility/
social networks may explain part of this
• R0 not constant - have been higher for reasons
of el Niño 2015/2016
• Second wave R predictions/estimations include
proportion susceptible (1-seroprevalence)
Rocklov, J., M. B. Quam, B. Sudre, M. German, M. U. Kraemer, O. Brady, Bogoch, II, J. Liu-Helmersson, A. Wilder-Smith, J. C. Semenza, M. Ong, K. K. Aaslav and K. Khan (2016).
"Assessing Seasonal Risks for the Introduction and Mosquito-borne Spread of Zika Virus in Europe." EBioMedicine 9: 250-256.
Towers S, Brauer F, Castillo-Chavez C, Falconar AK, Mubayi A, Romero-Vivas CM. Estimate of the reproduction number of the 2015 Zika virus outbreak in Barranquilla,
Colombia, and estimation of the relative role of sexual transmission. Epidemics. 2016.
Ospina J, Hincapie-Palacio D, Ochoa J, Molina A, Rúa G, Pájaro D, et al. The reproductive number of Zika in municipalities of Antioquia, Colombia: stratifying the potential
transmission of an ongoing epidemic. arXiv preprint arXiv:160905969. 2016.
Funk S, Kucharski AJ, Camacho A, Eggo RM, Yakob L, Edmunds WJ. Comparative analysis of dengue and Zika outbreaks reveals differences by setting and virus. bioRxiv.
2016:043265.
Ferguson NM, Cucunuba ZM, Dorigatti I, Nedjati-Gilani GL, Donnelly CA, Basanez MG, et al. EPIDEMIOLOGY. Countering the Zika epidemic in Latin America. Science.
2016;353(6297):353-4.

10. Implication for heard immunity threshold (assuming
it is constant):

11. Future scenarios (6 different stochastic simulations):
No interventions, R0 median at around 2.4-4.2 (black) & 3.6-6.3 (red)
Outbreaks here
below 1/1000?
Years Years
Ferguson NM, Cucunuba ZM, Dorigatti I, Nedjati-Gilani GL, Donnelly CA, Basanez MG, et al. EPIDEMIOLOGY. Countering the Zika epidemic in Latin America. Science. 2016;353(6297):353-

12. Summing up:
• Island settings: quick and intense outbreaks (high
R0) leading to high immunity on the population
(Capo Verde , French Polynesia, Martinique) a long
refractory period before further large outbreak
• Tropical region in urban settings: large outbreak
(first wave) with lower R0, and possibility of meta-
stability later on due to remaining none- immune
clusters
• Fringe zones of vectors: the transmission would
likely be only possible within seasonal windows

13. Implications:
- Interventions towards vectors may delay the burn
out of the epidemic and make advice for women
delaying pregnancy difficult
- El Nino can fuel certain years if seeding exists
- Establishment of sylvatic circulation
Vaccines/treatment:
- May be difficult to test efficacy as Zika outbreaks
may be sporadic and un-predictable
- Especially difficult assessing risk among pregnant
vaccinated mothers as the microcephaly risk is rare

14. Knowledge gaps:
• el Niño may fuel certain years if seeding exists
beyond what was accounted for increasing R0
• Sexual transmission can confound estimates
• Genetic difference in Aedes
• Enhancement & cross-protection uncertain
• Unaccounted connectivity may contribute to
different long-term patterns
• Establishment of sylvatic circulation uncertain
• Future Zika risk is difficult to assess before
more seroprevalence data become available

15. Thank you
Joacim.rocklov@umu.se
Specially to:
ECDC: Betrand Sudre, Herve Zeller, Vim Van Bortel
&
Team at Umeå University & ZikaPLAN