The Case for Reactive Mass Oral Cholera Vaccinations

Cholera outbreaks have had catastrophic impact on societies for centuries. Despite more than half a century of advocacy for safe water, sanitation and hygiene, approximately 100,000 cholera cases and 5,000 deaths were reported in Zimbabwe between August 2008 and by July 2009. Safe and effective oral cholera vaccines have been licensed and used by affluent tourists for more than a decade to prevent cholera. We asked whether oral cholera vaccines could be used to protect high risk populations at a time of cholera. We calculated how many cholera cases could have been prevented if mass cholera vaccinations would have been implemented in reaction to past cholera outbreaks. We estimate that determined, well organized mass vaccination campaigns could have prevented 34,900 (40%) cholera cases and 1,695 deaths (40%) in Zimbabwe. In the sites with endemic cholera, Kolkata and Zanzibar, a significant number of cases could have been prevented but the impact would have been less dramatic. The barriers which currently prevent the implementation of mass vaccinations, including but not only the cost to purchase the vaccine, seem insurmountable. A concerted effort of donors and key decision makers will be needed to offer better protection to populations at risk

Cases that would have been prevented by mass oral vaccination oral cholera vaccine in three endemic sites.

<p>Mass vaccination is presumed to be using the currently licensed two-dose oral cholera vaccine at varying response times and vaccine coverage.</p

Cases which had been reported before the outbreak was recognised, initiating potential reactive vaccination efforts.

<p>In Zimbabwe 24 hrs, 3 weeks and 6 weeks after the first 400 cases had been reported (and the outbreak recognised) the total number of cumulative cases were 501, 1,401 and 3,501 respectively (i.e. including the first 400).</p

Estimated reduction in cholera cases in Zanzibar.*

<p>3a: During the 2006–07 outbreak in Unguja following a <u>rapid</u> mass oral cholera vaccine campaign with 50% coverage. 3b: During the 2006–07 outbreak in Unguja following a <u>delayed</u> mass oral cholera vaccine campaign with 50% coverage. 3c: During the 2006–07 outbreak in Unguja following a mass oral cholera vaccine campaign with <u>maximum delay</u> and 50% coverage. 3d: During the 2006–07 outbreak in Pemba following a <u>rapid</u> mass oral cholera vaccine campaign with 50% coverage. 3e: During the 2006–07 outbreak in Pemba following a <u>delayed</u> mass oral cholera vaccine campaign with 50% coverage. 3f: During the 2006–07 outbreak in Pemba following a mass oral cholera vaccine campaign with <u>maximum delay</u> and 50% coverage. *See <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000952#pntd-0000952-t002" target="_blank">Table 2</a> for the time point symbolized by each arrow. Figures show the epicurve of the outbreak and the hypothetical number of cases prevented at response time.</p

Estimated reduction in cholera cases in Kolkata.*

<p>2b: During the 2003 outbreak following a <u>delayed</u> mass oral cholera vaccine campaign with 50% coverage. 2a: During the 2003 outbreak following a <u>rapid</u> mass oral cholera vaccine campaign with 50% coverage. 2c: During the 2003 outbreak following a mass oral cholera vaccine campaign with <u>maximum delay</u> and 50% coverage. 2d: During the <u>2004</u> outbreak following a <u>rapid</u> mass oral cholera vaccine campaign with 50% coverage. 2e: During the <u>2004</u> outbreak following a <u>delayed</u> mass oral cholera vaccine campaign with 50% coverage. 2f: During the <u>2004</u> outbreak following a mass oral cholera vaccine campaign with <u>maximum delay</u> and 50% coverage. *See <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000952#pntd-0000952-t002" target="_blank">Table 2</a> for the time point symbolized by each arrow. Figures show the epicurve of the outbreak and the hypothetical number of cases prevented at response time.</p

Estimated response times to mount a mass oral cholera vaccination campaign, using a single-dose vaccine.

<p>Estimated response times to mount a mass oral cholera vaccination campaign, using a single-dose vaccine.</p

Estimated reduction in cholera cases during the Zimbabwe 2008–09 outbreak.*

<p>1a: Following a <u>rapid</u> mass oral cholera vaccine campaign with 50% coverage. 1b: Following a <u>delayed</u> mass oral cholera vaccine campaign with 50% coverage. 1c: Following a mass oral cholera vaccine campaign with <u>maximum delay</u> and 50% coverage. *See <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0000952#pntd-0000952-t002" target="_blank">Table 2</a> for the time point symbolized by each arrow. Figures show the epicurve of the outbreak and the hypothetical number of cases prevented at response time.</p

The study sites.

<p>The study sites.</p

The number of cases that would have been prevented during the initial outbreak and in the years following vaccination.

<p>The total number of cases which would have been prevented during the first outbreak and in the years following mass vaccination using the currently licensed two-dose oral cholera vaccine with 50% vaccine coverage, and 85% PE in first 6 months, 60% PE from 6 to 18 months, and 20% for the following 3 years, at variable response times.</p