For the first time in India, ICMR scientists have confirmed conclusively that the spike protein (S-protein) antibody developed against the SARS-CoV2post the infection holds the ground for as long as 4-months. The study was conducted in Odisha.
However, the study finds a significant depletion of the antibody against the nucleocapsid protein (N-Protein) of the virus in nearly 40 per cent of cases.
As per a study done by ICMR Bhubaneswar scientists Hari Ram Choudhary, Debaprasad Parai and Girish Chandra Dash, among others, finds the waning of antibodies against nucleocapsid antigen protein but not a complete disappearance by the end of 16 weeks. Though 39.47% became seronegative in the qualitative assay, all the sera samples (100%) remained positive when tested in the quantitative assay.
Qualitative Vs Quantitative Assay
Any antibodies for infection with the result of yes or no is known as a “qualitative” test, whereas, an antibody test that quantifies how much antibody is called a "quantitative" test.
The interpretation of the ICMR study is when in around 4-months, antibody tests of the infected patients had shown negative, the quantitative tests have been positive which confirms the long batting by the IgG spike protein against the virus.
" A cohort of 76 confirmed COVID-19 positive healthcare and frontline workers from Bhubaneswar city was included in this study. Individuals were enrolled into the cohort after 28 days of being tested positive by RT-qPCR for SARS-CoV-2 virus and were followed up for 4 months with a periodic sample collection. No new or re-infection was reported by the cohort participants during the study period. The study was approved by the Institutional Human Ethical Committee. Informed signed consent was obtained from individuals before their enrolment into the study," informed scientist Hari Ram Choudhry and further observed that SARS-CoV-2 antibody titres were periodically (10 times) measured in 76 individuals (healthcare and frontline workers) who were COVID-19 positive by RT-PCR.
The Detail Results
- Median antibody titre was measured as 4.19 index at week 1, which started to wane from week 4 and decreased to 1.76 indexes at the end of week 16 in qualitative test detecting antibody against N-protein.
- Forty-six participants (60.53%) were found to have a reactive level of antibody till 16 weeks, whereas 30 (39.47%) become seronegative against the N-protein of SARS-CoV-2.
- All the participants (100%) were found positive in quantitative antibody testing at 16 weeks in comparison to 46 (60.52%) in qualitative testing.
The Big Finding
- The median concentration of IgG antibody against S-protein was recorded as 78.38 U/mL (IQR 40.54–161.9) and 212.8 U/mL (IQR 89.2–458.4) at week 1 and week 16, respectively, and the increment was statistically significant.
The Interpretation: S-protein is the target antigen of all vaccines. Because the S-protein binds with the ACE receptor cells in the lungs. An increase of the S-protein antibody between week number 1 to week 16 assumes significance. This is considered a game-changer against the virus when vaccination overdrive is on.
- High antibody level of 7.22 measured in 4 hospitalised patients.
- Males have higher antibody titre than females in both qualitative and quantitative tests at the end of 16 weeks.
- The respite is the difference is not statistically significant.
The Lead Author's Words
" Of the several ongoing studies around the world to track down the durability of anti-SARS-CoV-2 IgG have shown that IgG waning is quite fast in COVID-19 although no such study has been done with the Indian population to my best knowledge. In our study, 78.95% of participants were identified as symptomatic which is fairly opposite to the status of the symptoms of general population where most of the individuals (91%) reported as asymptomatic. We found around 40% of the serum samples were negative for IgG against N-protein at the end of 4 months, whereas a similar study in the USA found only 7.7% SARS-CoV-2 IgG negative after 3–6 months following symptom onset," observed Dr Choudhary.