EXTRA READING PRACTICE- RING VACCINATION

A World Health Organization expert meeting on Ebola vaccines proposed urgent safety and efficacy studies in response to the outbreak in West Africa. One approach to communicable disease control is ring vaccination of individuals at high risk of infection due to their social or geographical connection to a known case.

In the Ebola ça suffit(“Ebola, that’s enough”) ring vaccination trial, rings are randomised 1:1 to (a) immediate vaccination of eligible adults with single dose vaccination or (b) vaccination delayed by 21 days. Vaccine efficacy against disease is assessed in participants over equivalent periods from the day of randomisation. Secondary objectives include vaccine effectiveness at the level of the ring, and incidence of serious adverse events.

Ring vaccination trials are adaptive, can be run until disease elimination, allow interim analysis, and can go dormant during inter-epidemic periods.

Evaluating vaccine efficacy during outbreaks can be challenging due to the timescales involved, ethical concerns around research methods, and field operational challenges such as cold chain management and effective communication with those affected. Furthermore, to have adequate statistical power to detect a vaccine effect, a sufficient number of events must be observed. These challenges have again come to international attention due to the devastating epidemic of Ebola virus disease (EVD) in West Africa,where weak infrastructure for health and development exacerbate the difficulties inherent in communicable disease control and related interventional research.

An approach to increasing vaccine study power is to recruit those at highest risk of infection. A trial might thus recruit individuals who are socially or geographically connected to a case and therefore at increased risk of infection and developing disease within a few weeks. When implemented as a targeted programmatic public health measure, such an approach is described as “ring vaccination.”

A surveillance-containment strategy using ring vaccination was central to smallpox eradication in the 1970s. This contributed to the interruption of transmission in Africa, South America, and Asia.Ring vaccination with an efficacious vaccine might similarly help to control other communicable diseases by creating a buffer of immune people around each new case, thereby preventing further spread of the infection. Simulation studies suggest ring vaccination can contain outbreaks of infectious diseases with relatively low reproduction numbers (R0), such as EVD, for which R0 has been estimated at between 1 and 3.Some studies note that effective contact tracing, case isolation, and quarantine or monitoring of cases can have an effect equivalent to ring vaccination. A ring vaccination trial therefore tests both the vaccine and the approach.

QUIZ

The ring vaccination was previously found successful in preventing which desease?

Comment your answer in the comment box.

NB:THIS READING PASSAGE IS FOR EXTRA READING PRACTICE AND IT IS

 NOT INCLUDED ANY QUESTIONS.

Ref:Ref:BMJ. 2015; 351: h3740.