Limits...
Reactive vaccination in the presence of disease hotspots.

Azman AS, Lessler J - Proc. Biol. Sci. (2015)

Bottom Line: Owing to the global shortage of oral cholera vaccine, health officials must quickly decide who and where to distribute limited vaccine.We constructed metapopulation models of a cholera-like disease and compared simulated epidemics where: vaccine is targeted at areas of high or low transmission efficiency, where vaccine is distributed across the population, and where no vaccine is used.In highly connected settings (e.g. cities) when vaccinating early in the epidemic, targeting limited vaccine at transmission hotspots is often optimal.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, 615 North Wolfe St., Baltimore, MD 21205, USA azman@jhu.edu.

ABSTRACT
Reactive vaccination has recently been adopted as an outbreak response tool for cholera and other infectious diseases. Owing to the global shortage of oral cholera vaccine, health officials must quickly decide who and where to distribute limited vaccine. Targeted vaccination in transmission hotspots (i.e. areas with high transmission efficiency) may be a potential approach to efficiently allocate vaccine, however its effectiveness will likely be context-dependent. We compared strategies for allocating vaccine across multiple areas with heterogeneous transmission efficiency. We constructed metapopulation models of a cholera-like disease and compared simulated epidemics where: vaccine is targeted at areas of high or low transmission efficiency, where vaccine is distributed across the population, and where no vaccine is used. We find that connectivity between populations, transmission efficiency, vaccination timing and the amount of vaccine available all shape the performance of different allocation strategies. In highly connected settings (e.g. cities) when vaccinating early in the epidemic, targeting limited vaccine at transmission hotspots is often optimal. Once vaccination is delayed, targeting the hotspot is rarely optimal, and strategies that either spread vaccine between areas or those targeted at non-hotspots will avert more cases. Although hotspots may be an intuitive outbreak control target, we show that, in many situations, the hotspot-epidemic proceeds so fast that hotspot-targeted reactive vaccination will prevent relatively few cases, and vaccination shared across areas where transmission can be sustained is often best.

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Epidemic curves for hotspot () and non-hotspot () and timings for switching to different vaccination strategies. The populations in these simulations were symmetrically connected with cij(i ≠ j) = 0.2, 0.01, 0.0 (and cii = 1 − cij), from left to right (a–c), respectively, with 13.8% of the total population vaccinated (same simulations as panels g, i and k in figure 3). The y-axes are of different scale to highlight the shape of the different epidemic curves. Shaded areas represent the zones where a specific strategy is preferable with red representing hotspot-targeted vaccination, green representing pro-rata vaccination and blue representing non-hotspot-targeted vaccination. It should be noted that this scenario illustrates a small part of the decision space where all three strategies are optimal at some time throughout the epidemic.
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RSPB20141341F4: Epidemic curves for hotspot () and non-hotspot () and timings for switching to different vaccination strategies. The populations in these simulations were symmetrically connected with cij(i ≠ j) = 0.2, 0.01, 0.0 (and cii = 1 − cij), from left to right (a–c), respectively, with 13.8% of the total population vaccinated (same simulations as panels g, i and k in figure 3). The y-axes are of different scale to highlight the shape of the different epidemic curves. Shaded areas represent the zones where a specific strategy is preferable with red representing hotspot-targeted vaccination, green representing pro-rata vaccination and blue representing non-hotspot-targeted vaccination. It should be noted that this scenario illustrates a small part of the decision space where all three strategies are optimal at some time throughout the epidemic.

Mentions: We find that, when vaccine is limited, the best strategies for proactive vaccination differ significantly from those for reactive vaccination (i.e. vaccination after the start of the epidemic; figure 3 and the electronic supplementary material, S7 and S11). A general pattern emerges from our simulations where, over the course of the epidemic, hotspot-targeted vaccination is first preferred, then pro-rata vaccination, and finally targeting the non-hotspot (figure 3 and the electronic supplementary material, S7). However, depending on the connectivity and transmission potential, the continuum of optimal strategies may begin where pro-rata or non-hotspot targeting is preferred (e.g. figure 3o), or never transition from a point where hotspot targeting is preferred (e.g. figure 3f). In our simulations, the point at which hotspot targeting was replaced by pro-rata vaccination was before the global epidemic peak (e.g. figure 4) except for cases where the non-hotspot had an close to that of the hotspot. Thus, if the global peak has occurred, more cases will be averted if some vaccine is distributed to the non-hotspots, provided they can independently sustain transmission (i.e. ).Figure 3.


Reactive vaccination in the presence of disease hotspots.

Azman AS, Lessler J - Proc. Biol. Sci. (2015)

Epidemic curves for hotspot () and non-hotspot () and timings for switching to different vaccination strategies. The populations in these simulations were symmetrically connected with cij(i ≠ j) = 0.2, 0.01, 0.0 (and cii = 1 − cij), from left to right (a–c), respectively, with 13.8% of the total population vaccinated (same simulations as panels g, i and k in figure 3). The y-axes are of different scale to highlight the shape of the different epidemic curves. Shaded areas represent the zones where a specific strategy is preferable with red representing hotspot-targeted vaccination, green representing pro-rata vaccination and blue representing non-hotspot-targeted vaccination. It should be noted that this scenario illustrates a small part of the decision space where all three strategies are optimal at some time throughout the epidemic.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4262159&req=5

RSPB20141341F4: Epidemic curves for hotspot () and non-hotspot () and timings for switching to different vaccination strategies. The populations in these simulations were symmetrically connected with cij(i ≠ j) = 0.2, 0.01, 0.0 (and cii = 1 − cij), from left to right (a–c), respectively, with 13.8% of the total population vaccinated (same simulations as panels g, i and k in figure 3). The y-axes are of different scale to highlight the shape of the different epidemic curves. Shaded areas represent the zones where a specific strategy is preferable with red representing hotspot-targeted vaccination, green representing pro-rata vaccination and blue representing non-hotspot-targeted vaccination. It should be noted that this scenario illustrates a small part of the decision space where all three strategies are optimal at some time throughout the epidemic.
Mentions: We find that, when vaccine is limited, the best strategies for proactive vaccination differ significantly from those for reactive vaccination (i.e. vaccination after the start of the epidemic; figure 3 and the electronic supplementary material, S7 and S11). A general pattern emerges from our simulations where, over the course of the epidemic, hotspot-targeted vaccination is first preferred, then pro-rata vaccination, and finally targeting the non-hotspot (figure 3 and the electronic supplementary material, S7). However, depending on the connectivity and transmission potential, the continuum of optimal strategies may begin where pro-rata or non-hotspot targeting is preferred (e.g. figure 3o), or never transition from a point where hotspot targeting is preferred (e.g. figure 3f). In our simulations, the point at which hotspot targeting was replaced by pro-rata vaccination was before the global epidemic peak (e.g. figure 4) except for cases where the non-hotspot had an close to that of the hotspot. Thus, if the global peak has occurred, more cases will be averted if some vaccine is distributed to the non-hotspots, provided they can independently sustain transmission (i.e. ).Figure 3.

Bottom Line: Owing to the global shortage of oral cholera vaccine, health officials must quickly decide who and where to distribute limited vaccine.We constructed metapopulation models of a cholera-like disease and compared simulated epidemics where: vaccine is targeted at areas of high or low transmission efficiency, where vaccine is distributed across the population, and where no vaccine is used.In highly connected settings (e.g. cities) when vaccinating early in the epidemic, targeting limited vaccine at transmission hotspots is often optimal.

View Article: PubMed Central - PubMed

Affiliation: Department of Epidemiology, Johns Hopkins University Bloomberg School of Public Health, 615 North Wolfe St., Baltimore, MD 21205, USA azman@jhu.edu.

ABSTRACT
Reactive vaccination has recently been adopted as an outbreak response tool for cholera and other infectious diseases. Owing to the global shortage of oral cholera vaccine, health officials must quickly decide who and where to distribute limited vaccine. Targeted vaccination in transmission hotspots (i.e. areas with high transmission efficiency) may be a potential approach to efficiently allocate vaccine, however its effectiveness will likely be context-dependent. We compared strategies for allocating vaccine across multiple areas with heterogeneous transmission efficiency. We constructed metapopulation models of a cholera-like disease and compared simulated epidemics where: vaccine is targeted at areas of high or low transmission efficiency, where vaccine is distributed across the population, and where no vaccine is used. We find that connectivity between populations, transmission efficiency, vaccination timing and the amount of vaccine available all shape the performance of different allocation strategies. In highly connected settings (e.g. cities) when vaccinating early in the epidemic, targeting limited vaccine at transmission hotspots is often optimal. Once vaccination is delayed, targeting the hotspot is rarely optimal, and strategies that either spread vaccine between areas or those targeted at non-hotspots will avert more cases. Although hotspots may be an intuitive outbreak control target, we show that, in many situations, the hotspot-epidemic proceeds so fast that hotspot-targeted reactive vaccination will prevent relatively few cases, and vaccination shared across areas where transmission can be sustained is often best.

Show MeSH
Related in: MedlinePlus