The results of the fourth COVID-19 national serosurvey (June-July 2021) of India have been analysed. Much needed data of vaccine generated antibodies have been reported world first as recorded in Indian population on the ground in real. More than two-thirds of (67.6%) Indian population developed antibodies against the infection. This includes natural immunity build up due to infection and vaccine generated antibodies. Eleven states: Madhya Pradesh, Rajasthan, Bihar, Gujrat, Chhattisgarh, Uttarakhand, Uttar Pradesh, Andhra Pradesh, Karnataka, Tamil Nadu, and Odisha had sero positivity of >67.6%which was the national average. Ten other states registered < 67.6% seroprevalence were: Punjab, Telangana, Jammu and Kashmir, Himachal Pradesh, Jharkhand, West Bengal, Haryana, Maharashtra, Assam, and Kerala. Single dose vaccination of 24% population added 19% seroprevalence in the population whereas 13% full vaccination increased 28% individuals registered antibodies. The highest (90%) seroprevalence was registered among the individuals who have taken both vaccine doses followed by HCWs (85%). Seroprevalence in 85-90% population might be the threshold for herd immunity which delayed or possibly stopped the third COVID-19 wave in India.
The results of all six serosurveys of Delhi (India) have been analysed. The first serosurvey held in June-July 2020 found seroprevalence in 22.9% population. The second, third, and fourth survey conducted in August, September, and October registered 29.1%, 25.1%, and 25.5% seropositivity, respectively. The seroprevalence was increased to a larger extent of 56.1% in the fifth (January 2021) survey due to the accumulation of antibodies among the residents in three pandemic waves that hit the city in June, September, and November 2020. The last and the fourth bigger wave that hit the city in April 2021 caused almost all (97%) citizens to develop antibodies against the natural COVID-19 infection. The seroprevalence in women was marginally higher (90%) than in men (88%). The seroprevalence was highest (92%) among the individuals above 50 years of age followed by 18-49 years of age (90%) and 82% in below 18 years of age. The residents who were vaccinated with Covishield produced slightly higher antibodies (95%) than Covaxin (93%). In Delhi,one dose or two doses vaccination could increase seroprevalence to 95% that was the maximum which vaccination could generate. The unvaccinated population had seroprevalence of 85%. A maximum enhancement of 13% seroprevalence was recorded upon vaccination with one or two doses.
The first and second serosurvey results of COVID-19 antibodies in Dharavi and Cuffe Parade slums (Mumbai, India) were studied. The seroprevalence data of the slums explained the zero novel coronavirus cases reported in the slum dwellers verified first in real on the ground the concept of much needed herd immunity against the pandemic. First serosurvey data showed that more than half (57%) of the population of Dharavi was infected with the virus. The antibodies were waned off in two month time and diminished to 45%, as found in the second survey conducted after two months of the first survey. The antibodies prevalence was highest at 75% in Cuffe Parade slums of Mumbai. Initially, Dharavi slums were a hotspot of novel coronavirus which later became nearly a no-new infection zone. The herd immunity acquired in Dharavi residents stopped the new infection. One million Dharavi slum dwellers living in a crowded semi-isolated cluster mimic the petri-dish model of a human population which is now a near COVID-19 free zone due to the presence of antibodies in the residents. The infection rate in Maharashtra, India, and Dharavi slums was compared. The concept of herd immunity that occurred on the ground in real has been first established. The research is very useful to vaccinate populations to eradicate the pandemic from the globe.
The breakthrough infections (BTI) during the Delta wave in the general population have been investigated. The BTI reported in the city of Gurugram (Haryana, India) in the month of August, September, and October 2021 were studied. The monthly BTI in August, September, and October 2021 were 26%, 41%, and 76%, which caused an increase in the monthly caseload to 167, 150, and 206 cases, respectively. Mostly, the patients who had comorbidities developed BTI. However, the BTI reported in the Delta wave did not cause a surge in new cases. The surge was noticed only after the emergence of the Omicron variant of the SARS- CoV-2 virus. In Gurugram, 78.3% sero prevalence recorded in September 2021 was due to vaccination and higher infection rate of 59,921 monthly cases reported in April 2021.
The self-referred serosurvey data showed that the whole of India, 31% population has SARS-CoV-2 antibodies. Seroprevalence was higher in females (35%) than males (30%). The seropositivity in Ahmedabad, Jaipur, Bangalore, and Delhi increased monotonously from July to December. Seropositivity in big cities of India was as high as 63.8% in Bangalore followed by Delhi (54.9%) and Kolkata (54.6%). In cities (Mumbai, Chennai, Pune, Coimbatore, Surat, Visakhapatnam, Kolkata, and Nagpur) antibodies prevalence first increased with time after a threshold it started decreasing in 4 month time in most of the cities. Intergeneration age dependent seropositivity for both males and females showed an “M-shaped” pattern. The seroprevalence versus monthly infection rate in Delhi and Kolkata showed an increase in seroprevalence with the caseload. In Chennai, the caseload of new infections decreased while seropositivity increased. In the case of Mumbai, seropositivity increased with increase in the caseload in the beginning till October, after that with decrease in the caseload seroprevalence also diminished. In none of the cities, the amount of antibodies titers was enough to stop the second wave of the pandemic.
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