Joacim Rocklöv: What scenarios for the epidemiological pattern of Zika infection in the future?

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

Virus, Vector & Susceptible people

The Zika Epidemic

Microcephaly & GBS

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Studies of relevance for Zika preparedness

In preparationSudre B et al.

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

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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

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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.

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. Eurosurveillance : bulletin Europeen sur les maladies transmissibles = European communicable disease bulletin. 2016;21(18).

Travelling & risk modeling

• Estimating number of travellers from catchment areas (polygons) around airports in Aedessuitable 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 vectorialcapacity. 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 Africaand 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.

- 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. Eurosurveillance : 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.

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.

Implication for heard immunity threshold (assuming

it is constant):

Future scenarios (6 different stochastic simulations):No interventions, R0 median at around 2.4-4.2 (black) & 3.6-6.3 (red)

Outbreaks herebelow 1/1000?

Years YearsFerguson 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.

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

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

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

Thank you

[email protected]

Specially to:ECDC: Betrand Sudre, Herve Zeller, Vim Van Bortel

&

Team at Umeå University & ZikaPLAN