The burning topic of discussion of today’s vaccine roll out is ‘How much is the efficacy of the vaccine?’ But is this the real sphere of concern?
The prime logic behind clinical development was worked out by statisticians over decades ago.
Phase-I: Small groups of people receive the trial vaccine to evaluate the vaccine safety and dosage.
Phase-II: Clinical study is expanded and vaccine is given to people who have characteristics similar to those for whom the new vaccine is intended.
Phase-III: Vaccine is given to thousands of people and tested for efficacy and safety.
For Licensure, the demonstration of Vaccine Efficacy (VE) is fundamental.
Generally, vaccine efficacy is defined as the % reduction in disease incidence in a vaccinated group compared to an unvaccinated group under optimal conditions, with 100% efficacy corresponding to zero incidence in vaccinated persons.
It is crucial to note that 98% efficacy does not mean that 98 out of 100 will not contract the virus. It indicates a 98% reduction in disease occurrence among the vaccinated group, or a 98% reduction in the number of cases you would expect if they have not been vaccinated.
The length of this study, under ordinary scenario, is 1-4 years. But under extraordinary situations such as Public Health Emergencies (PHE), vaccine companies hope to get results much sooner—in a year or less.
The 2013-2016 West-African Ebola outbreak has broken new ground in speed and study design and has set a precedent for vaccine evaluation during PHE. ERVEBO, Ebola Zaire Vaccine, manufactured by Merck Sharp & Dohme Corp, was given expanded access in African Countries with WHO, MSF, and other groups taking lead in implementation. It was necessary to manufacture doses to support outbreak response and restrict the onset of a new outbreak. Through this effort, more than 300,000 people were vaccinated during the 2018–2020 Ebola outbreak in the Democratic Republic of the Congo. Based on lessons learned from such outbreaks, the WHO’s guidelines aims to reduce the time lag between the declaration of a PHE and the availability of medical countermeasures, especially vaccines.
Assessing vaccine efficacy during such emergencies presents unique challenges such as the changing epidemiology in incidence. This may make it difficult to obtain sufficient clinical data to directly support vaccine efficacy. For this reason, it can be important to collect as much serological data as possible in the trials. Such data could potentially support other uses of the vaccine in the interim between trial completion and licensure, including temporary approval through Emergency Use Authorization (EUA).
Vaccine Efficacy is an individual-level measure made during a clinical trial, providing information about how well a vaccine works under the conditions of the clinical trial.
While Vaccine Effectiveness tells us how well a vaccine works under real-world conditions once people outside of clinical trials receive the vaccine – for example, people of different ages or ethnicities, residents of different geographical locations, and subpopulations not studied at all or studied in groups too small to produce precise estimates of vaccine efficacy.
This establishes that effectiveness is the substantial criteria to be considered over the numerical value of efficacy.
Efficacious vaccines not only protect the immunized, but can also reduce disease among unimmunized individuals in the community through herd protection.
Regardless of a vaccine’s efficacy and which vaccine is taken, one thing is certain: Vaccination is a proficient tool to reduce the burden of severe infections and hospitalisations, which in itself is THE VICTORY!