The Health Ministry has decided to increase the interval between first and second doses of Covishield to up to eight weeks in the ongoing covid-19 vaccination drive. This decision was taken following the data of the global trials of AZD122 which shows that extending the duration of doses to 12 weeks has increased its efficacy much more. While the interim findings reported following the trials in the US, Chile, and Peru that the vaccine had an efficacy of 79 percent even when the second dose of the vaccine was given four weeks after its first dose.
Ministry of Health and Family Welfare has decided to increase the dosing interval on the recommendation of two expert groups namely the *National Technical Advisory Group on Immunisation (NTAGI) and the National Expert Group on Vaccine Administration for Covid-19 (NEGVAC). The groups examined the scientific evidence from the clinical trials of the Covishield vaccine and concluded that the protection provided by the vaccine is enhanced if the second dose is administered in between 6-8 weeks.
Report from other countries
The report on trials of AZD1222 vaccine from other countries also states that the efficacy of the vaccine was increased when its second dose was given on the gap of six weeks after the first dose. The efficacy of the vaccine AZD1222 was around 54.9 percent when the second dose was given on the gap of fewer than six weeks during the phase 3 clinical trial across Brazil, UK, and South Africa. The report further states that the efficacy of the vaccine increased to 59.9 percent when its second dose was administered 6-8 weeks after its first dose. It increased to 63.7 percent when the second dose was given after the gap of 9-11 weeks while it increased to 82.4 percent when the interval increased to 12 weeks or more.