NEW YORK (Reuters Health) – A single-dose regimen of inactivated whole-cell oral cholera vaccine protects adults and children over 5 from infection for at least two years, according to a randomized trial conducted in Bangladesh.
Oral cholera vaccines are typically given as a two-dose regimen and confer protection against cholera for at least five years. In many settings, the second dose can be challenging, so immediate vaccine protection after the initial dose is highly desirable.
Dr. Firdausi Qadri from the International Center for Diarrheal Disease Research Bangladesh, in Dhaka, and colleagues earlier found that a single dose of the Shanchol oral cholera vaccine provided 40% protection against all episodes of cholera and 63% protection against severe episodes during six months of follow-up.
In the current report, they report results through two years of follow-up.
The overall protective efficacy at two years was 39%, with 50% protective efficacy against severe episodes of cholera, the researchers report in The Lancet Infectious Diseases, online March 14.
Among children under 5, there was no protective efficacy overall or against severe cholera episodes.
In contrast, among participants aged 5 years to 15 years at vaccination, protective efficacy was 52% against all cholera and 71% against severe cholera. For participants aged 15 years or older, protective efficacy was 59% against all cholera and 59% against severe cholera.
“The global stockpile of inactivated whole-cell oral cholera vaccine (OCV) has often been deployed in settings with natural or man-made humanitarian disasters, in which completion of a two-dose regimen could be challenging,” the researchers note. “Our results indicate that when such emergencies occur in populations with endemic cholera, the challenges of successfully completing a two-dose regimen should not deter deployment of OCV, because older children and adults will be protected for at least 2 years by a single dose.”
“Also, because the global production of inactivated whole-cell OCV is limited, a scarcity of doses might make it desirable in cholera-endemic settings to deploy a single-dose regimen to older children and adults, reserving a two-dose regimen for young children,” they write. “Finally, because the age-related differences in vaccine protection in our study might have been due to a greater pre-existing anticholera natural immunity in the older participants, our findings provide indirect support to the notion that boosting after the standard two-dose primary series with inactivated whole-cell OCVs might require only a single dose. This hypothesis should be evaluated in future studies.”
Dr. Lorenzo Pezzoli from the World Health Organization Cholera Team, in Geneva, Switzerland, told Reuters Health by email, “I do not expect that this study will change the way we use OCV for now. WHO already recommends using a single dose of OCV in certain conditions that may not require longer-term protection (emergency situations like outbreak response) and will continue to do so (a second dose is then recommended in case of persistence of risk to ensure longer protection). You can find the recommendations in the WHO Cholera Vaccine Position Paper.” (https://bit.ly/2Gngi34)
“One important point for public-health practitioners is that no matter the efficacy and duration of protection, OCV alone will not solve the cholera problem (especially in countries like Bangladesh),” he explained. “OCV is a great tool and has been a game changer for cholera control, but vaccination has to be followed by more definite improvements in water and sanitation. Otherwise, as soon a protection wanes, cholera will reappear. This is the strategy currently advocated by the Roadmap for Cholera Elimination by 2030 launched by the Global Task Force on Cholera Control.”
Dr. Qadri did not respond to a request for comments.
The Bill and Melinda Gates Foundation provided funding to the International Vaccine Institute for the study.
SOURCE: https://bit.ly/2HXX0OX
Lancet Infect Dis 2018.
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