The study stated that the test positivity rate crossing an example threshold value of 0.5% in the period between two Covid-19 waves in a region could provide a timely alert for the emergence of the next wave.
The study suggested employing a technique called “rapid-response vaccination” in a hypothetical district immediately upon the test positivity crossing the threshold of 0·5%, to reduce the local resurgence of Covid-19 at the start of another wave.
Dr Samiran Panda, chief of the ICMR’s epidemiology and communicable diseases division, told TOI, “As per this technique, we concentrated on a vaccination strategy that prioritises the widest possible coverage with single-dose vaccination, in which it takes one month to cover 75% of the population aged 18 years or above with a single dose. We found that such rapid and focused vaccination efforts alone could substantially reduce mortality by up to 37% in a district witnessing the beginning of another Covid wave.”
He said the appropriate test positivity rate thresholds for other districts in India could be arrived at to employ rapid vaccination strategies to cut down resurging infections during the start of another wave.
As per the study, if non-pharmaceutical measures, such as mandatory mask wearing, restrictions on gatherings and stay-at-home, could be adopted along with rapid response vaccination, transmission could reduce by 25%. “If these measures are implemented for one month in the district at the same time as the vaccination drive, the model projections suggest that overall deaths could be reduced by up to 45% for a Covid infection with reproduction rate of 2, and by 30% for that with a reproduction rate of 3,” he said.
The model included practical assumptions on the effect of vaccination, including that, once vaccinated, people take an average three weeks to develop immunity. Thus, a single vaccine dose could offer 60% protection against severe disease and death, but could not protect against contracting Covid itself, the study findings indicated.
The vaccine efficacy was based on published estimates of 76% protection from symptomatic infection, following a single dose of the Oxford-AstraZeneca vaccine, known as Covishield in India.
Giving another example of rapid and agile vaccination protocol, Dr Panda said, “Clearing off trees in the path of a fast-raging forest fire will ensure that gradually, there would not be any trees for the fire to catch on to. It is like creating a fence to prevent the fire from progressing further. Similarly, when a district crosses its threshold test positivity rate indicating a resurgence in infections, vaccination in the surrounding districts with lower test positivity rate could be ramped up to prevent the infection catching on to them.” This is also to tackle the limited stores of vaccines and using them smartly at times of a rise in infections.