We have developed Covid vaccines that are highly efficacious ( 94%) as early as December 2020. Yet in the mid 2021, the world reeled under the attack of Delta and the Omicrons.
Today we are going to discuss two aspect of the Covid Vaccines:
- Vaccine Efficacy (VE)
- Immunological Memory ( IM)
Let us classify all the popular covid vaccines into two broad categories:
( They contain only the DNA, RNA or the RBD ( Receptor Binding Domain) or whole Spike protein only. )
Both the mRNA vaccines and the Protein Subunit vaccines have shown 90% + efficacy in the short term clinical trial protocols.
USA has adopted only two mRNA ( Pfizer, Moderna) and one Recombinant Spike protein, rS ( Novavax) agents. Both have proven 90%+ efficacy. It also started vaccinating its citizen quite early by December 2020.
Delta struck USA around July of 2021 and cases started peaking in the August 21. Immunological memory was found to be short for both the component vaccines.
Israel and then USA started their 3rd dose followed by 4th dose for the vulnerable. Over all immunological memory was 12 week.
Immunological memory for the component vaccines like mRNA and Protein subunits are very low around 6 months. You need to vaccinate every 6 month for a perennial infection or coincide them with the peak of a seasonal infection.
Vaccine Efficacy is low but immunological memory is longer in the whole virus vaccines.
- Killed– Covaxin, Sinopharm and Sinovac
- Live Viral Vector ( contains a live Adeno virus: Covishield, CanSino, Gamaleya)
Whole viruses would induce longer immunity. The live ones stimulate longer and robust immunity. But the vaccine efficacy never reaches 90%. Between the two, live viral vector vaccines have more efficacious and confer longer immunity.
Covishield gives you longer protection and is more efficacious than Covaxin.
In Respiratory pathogens the cut off line for VE is 60%. Accordingly all the vaccines ( Covaxin, Covishield, Covovax and Corbevax) has been given EUA.
The component vaccines are useful for rapid immunisation for immunocompromised and vulnerable children or during an epidemic.
But in other times particularly in children who have a strong innate immunity they may not be that useful. The duration of protection is very low.
Second Generation Vaccines.
All the present bouquets of vaccines can be called as First Generation vaccine.
I believe the technology adopted by Edward Jenner 1790s is already 200 years old. For respiratory pathogens, local immunity is more important than the induced humoural immunity.
Zoonoses are frequent now. Globalisation has led the virus from Wuhan to spread to Italy and from Congo to USA faster than we had imagined.
We must rethink our vaccine technology for the EIDs : Emerging Infectious Diseases.
Joshua Lederberg, the pioneer Nobel laureate says:
“The Single Biggest Threat to
Man’s continued Dominance on this Planet is
VIRUS.”
ରମାକାନ୍ତ ମହାପାତ୍ର
Dr Ramakanta's Ideas 