IISER study finds 15% sero survey samples in Pune might never develop antibodies against Covid
Samples were collected from the city’s five most affected wards and tested positive for antibodies indicating that they were infected at one point of timeUpdated: Nov 21, 2020, 16:31 IST
A follow-up study by city’s Indian Institute of Science Education and Research (IISER) on the pilot sero (seroprevalence) survey has found that about 85% samples tested positive for neutralising antibodies which can act effectively against SARS-CoV-2 which causes Covid-19, while the remaining samples tested negative.
The samples were collected from the city’s five most affected wards and tested positive for antibodies indicating that they were infected at one point of time. However, 15% of the samples tested for neutralising antibodies showed no such activity hinting that this is the vulnerable group if a second wave hits Pune.
The study was conducted by multiple institutes and led by IISER and Savitribai Phule Pune University (SPPU). It was a follow up of the pilot sero survey conducted in July and made public in August. Random samples were collected from 1,659 asymptomatic individuals from five sub-wards in Yerawada, Kasbapeth-Somwarpeth, Rastapeth-Ravivarpeth, Lohiyanagar-Kasewadi and Navipeth-Parvati. Out of these, 51% had tested positive for antibodies. Experts involved in the study had said that although it needs to be further studied if these antibodies have the neutralising activity to fight against SARS-CoV-2.
The paper states: “From the 857 (receptor-binding-domain) RBD-IgG (Immunoglobulin G) positive sera, 697 samples were randomly selected and tested for the ability to inhibit the binding of SARS-CoV-2 RBD to human angiotensin converting enzyme-2 (ACE-2) using a specific ELISA-based surrogate virus neutralisation test (sVNT)20. At least 85•1% of the RBD-IgG positive sera were sVNT positive.”
Dr Aurnab Ghose, associate professor, IISER and also the corresponding author of the paper said, “Out of the samples that we tested to detect neutralising antibodies against Covid, we found that 85% did show the neutralising properties which are the early indicators of population level immunity loosely also referred to as herd immunity. However, in the remaining 15% of the samples there were no traces of such antibodies which states that even though they might have been infected at one point they are vulnerable in the second wave.”
The paper further states: “While 57•2% of the 18-30 years age-group showed ≥50% inhibition, this increased to 64% in the 31-50 years category and became 75% in the population above 50 years (p<0.001 or less than one in a thousand chance of being wrong). However, no association was found with sex. An explanation for the age factor could be the association of RBD-binding antibody levels with age, as high sVNT values are likely to be positively correlated with high RBD-binding activity.”
Dr Ghose said the samples that tested positive for neutralising antibodies showed varied proportions of the antibodies ranging from as less as 25% to more than 75% depending on age groups.
The paper also stated that the presence of chronic illness, travel history, working status, exposure to Covid patients, history of quarantine, participation in social gatherings, self/family members working in health care set up did not reveal any significant association with sero-positivity. While infection risk was similar between men and women, the sero-prevalence (presence of antibodies) in the elderly population (65+ age-group) was lower than the younger population. This observation is in contrast to what has been reported from Delhi and Mumbai.
Dr Ghose said that it will take further studies to identify these vulnerable groups which will help the administration to keep a close watch on such vulnerable populations.
A similar study was done by BJ Medical College based on the number of plasma donors who approached the hospital for blood donation. The study found that of the 351 plasma donors who were tested for antibodies only 237 tested positive and could donate plasma for the treatment of Covid patients which is 67.52% of those tested positive for the antibodies.
Both the studies indicate that while there is a considerable chance that a person who has been infected once is likely to be re-infected even if they do test positive for antibodies.