The current revisions have been done following several case studies and clinical data which showcased a heightened immune response when the second COVID-19 jab was taken many weeks after the first dose.
Initial recommendations suggested that the Covishield vaccine be taken 4-6 weeks after the first dose (which was further revised to 4-8 weeks). However, clinical research has been able to find that the vaccine, which carries an 80-90% efficacy rate was able to provide enhanced protection when the second dose was taken at least 8 weeks after.
In a study published in the medical journal, The Lancet, vaccine efficacy and immune response were also greatly derivative of the time gaps. Researchers found that with certain COVID vaccines, including Covishield, or the Oxford-Astrazeneca one, the longer the gap, the higher the efficacy of the vaccine. It was observed that the vaccine efficacy and immune response was significantly better, at 81.3% when the doses were given in an interval of 12-16 weeks, in comparison to a 50-60% efficacy when spaced 6 weeks or less apart.