Vaccination during a pandemic - a public health challenge
Since the emergence of COVID 19 virus, scientists all over the world are working at breakneck speed to develop a vaccine. Development of a vaccine is not a competitive race to the finish as it must pass through a stringent process of evaluation. The process includes vaccines’ immunogenicity, duration of immunity, efficacy of protection, interaction with other antigens, dosage, route of administration, packaging, and thermostability and expected adverse events and safety. Efficacy of a new vaccine is measured in clinical trials under ideal conditions, whereas its effectiveness is measured in the field under actual program conditions. In normal circumstances, vaccine development is a prolonged process, averaging over 10 years from start to finish . To meet the urgent, need a COVID 19 vaccine may be available in a much shorter-term frame, at the earliest in 18 months. [1,3,4] This will be possible as a result of the unprecedented coordinated and combined global effort of the scientific and National Regulatory Authority (NRA). The conclusive proof of vaccine safety and efficacy is “standard corelates of protection of vaccinees” (SCPV) set by WHO and NRA. One of the major criteria for authorization of a vaccine is its protective efficacy measured by the outcome of disease occurrence (clinical end point) in experimental and control group. As it is a lengthy process instead of the clinical endpoint (i.e. disease) “intermediate end point” of antibody generation is used as a surrogate.  The Food & Drug administration (FDA) of US department of Health and Human services has set the recommended Primary efficacy end point (PEEP) estimates at 50% with an alpha-adjusted confidence interval of >30% around the primary efficacy endpoint point estimate. .
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