Thread by @vipintukur

Is there any role of large-scale vaccination in containing the ongoing surge in #India? The current estimate of herd immunity threshold is around 60%-70% based on the estimate with old variant #D614G. 1/

With the advent of new, more transmissible #variants, the estimate for a herd immunity threshold may further go up. The pace of inoculation is very sluggish, inoculated a meagre 2.0 % of our population with 2 doses! May take few years to reach anywhere near the threshold 2/

We are currently on the ascending limb of an outbreak propelled by a highly transmissible virus with a high reproduction number (Ro). Further, there is confusion over what it means to reach herd immunity 3/

The ‘herd immunity’ threshold is the point at enough people are immune (by vaccination or previous infection) to prevent a new epidemic from starting. It is NOT the point at which an ongoing epidemic disappears. When you reach ‘herd immunity, a pandemic is far from over 4/

The problem is while a new epidemic can no longer start from scratch once you reach herd immunity. When we reach this point, we will still have the old epidemic underway. All those who are currently infected will continue to transmit after you reached herd immunity threshold 5/

They just will infect fewer than one additional person, on average. So, the achievement of the herd immunity threshold may not prevent the ongoing outbreak but may significantly diminish the chances of a future surge 6/

Strict implementation of non-pharmaceutical interventions around the herd immunity threshold is a very efficient way to reduce the total size of the epidemic, by reducing the overshoot. For this, we need strict lockdowns 7/

Still, large scale vaccination may count provided we use them judiciously. We need to be judicious while planning our vaccination drive. It should have a significant impact at the population level and should counter any future surge 8/

To attempt achieving herd immunity with the current vaccines We have the example of the Brazilian city of #Manaus where a more virulent variant (P.1) ripped through the high ‘seropositivity cover’ of past infections to cause a huge outbreak 9/

Put simply, the game has changed, and a successful global rollout of current vaccines by itself is no longer a guarantee of victory. Still, large scale vaccination may count provided we use them judiciously.

Ideally, the public health policies should be guided by science, not by the programmatic feasibility. Every effort should be made to take an evidence-based decision that may serve immediate & future purposes 10/

Bottom-line: There is going to be a limited impact of vaccination on the ongoing surge. Vaccines may have some utility for individual protection, but they may have little impact on the course of the ongoing pandemic. My views summarize here 👇 11/
thehindubusinessline.com/specials/pulse…

Judicious selection of vaccines goes a long way in containing the outbreak. Take the case of #Seychelles, which has chosen #Sinopharm & #Covishield, still facing a new surge in cases despite vaccinating >69% of its population w/ 2 doses! 12/
bloomberg.com/news/articles/…

In contrast, take the case of #Israel. Despite vaccinating less share of its population (59%) with 2-doses than Seychelles, they could bring the curve to baseline & has achieved zero-covid deaths! The difference: type of vaccine used (Pfizer’s mRNA) 13/

So, the message is loud & clear. Use vaccines judiciously! Do not rely exclusively on vaccines. They are poor substitute to strict implementation of non-pharmaceutical interventions. Even Israel had to go through multiple lockdowns @jo_da123 14/
thehindubusinessline.com/specials/pulse…