Delhi, the national capital of India, has experienced multiple SARS-CoV-2 outbreaks in 2020 and reached population seropositivity of over 50% by 2021. During April 2021, the city became overwhelmed by COVID-19 cases and fatalities, as a new variant B.1.617.2 (Delta) replaced B.1.1.7 (Alpha). A Bayesian model explains the growth advantage of Delta through a combination of increased transmissibility and reduced sensitivity to immune responses generated against earlier variants (median estimates; ×1.5-fold, 20% reduction). Seropositivity of an employee and family cohort increased from 42% to 87.5% between March and July 2021, with 27% reinfections, as judged by increased antibody concentration after a previous decline. The likely high transmissibility and partial evasion of immunity by the Delta variant contributed to an overwhelming surge in Delhi.

Genomic characterization and epidemiology of an emerging SARS-CoV-2 variant in Delhi, India.

Persuading people to mask Even in places where it is obligatory, people tend to optimistically overstate their compliance for mask wearing. How then can we persuade more of the population at large to act for the greater good? Abaluck et al . undertook a large, cluster-randomized trial in Bangladesh involving hundreds of thousands of people (although mostly men) over a 2-month period. Colored masks of various construction were handed out free of charge, accompanied by a range of mask-wearing promotional activities inspired by marketing research. Using a grassroots network of volunteers to help conduct the study and gather data, the authors discovered that mask wearing averaged 13.3% in villages where no interventions took place but increased to 42.3% in villages where in-person interventions were introduced. Villages where in-person reinforcement of mask wearing occurred also showed a reduction in reporting COVID-like illness, particularly in high-risk individuals. —CA 

https://www.science.org/cms/asset/64c2ff71-2638-40f3-af84-4730cf0eabc0/science.abi9069.v1.pdf

Impact of community masking on COVID-19: A cluster-randomized trial in Bangladesh

In April 2021, after successfully enduring three waves of the SARS-CoV2 pandemic in 2020, and having reached population seropositivity of about 50%, Delhi, the national capital of India was overwhelmed by the fourth wave Here, we trace viral, host, and social factors contributing to the scale and exponent of the fourth wave, when compared to preceding waves, in an epidemiological context Genomic surveillance data from Delhi and surrounding states shows an early phase of the upsurge driven by the entry of the more transmissible B117 variant of concern (VOC) into the region in January, with at least one B117 super spreader event in February 2021, relatable to known mass gatherings over this period This was followed by seeding of the B1617 VOC, which too is highly transmissible, with rapid expansion of B16172 sub-lineage outpacing all other lineages This unprecedented growth of cases occurred in the background of high seropositivity, but with low median neutralizing antibody levels, in a serially sampled cohort Vaccination breakthrough cases over this period were noted, disproportionately related to VOC in sequenced cases, but usually mild We find that this surge of SARS-CoV2 infections in Delhi is best explained by the introduction of a new highly transmissible VOC, B16172, with likely immune-evasion properties; insufficient neutralizing immunity, despite high seropositivity; and social behavior that promoted transmission

/pdf/genomic-characterization-and-epidemiology-of-an-emerging-4a233kf5zp.pdf

Genomic characterization and Epidemiology of an emerging SARS-CoV-2 variant in Delhi, India

Background The COVID-19 Delta pandemic wave in India surged and declined within 3 months; cases then remained low despite the continued spread of Delta elsewhere. Here we aim to estimate key epidemiological characteristics of the Delta variant based on data from India and examine the underpinnings of its dynamics. Methods We utilize multiple datasets and model-inference methods to reconstruct COVID-19 pandemic dynamics in India during March 2020 - June 2021. We further use model estimates to retrospectively predict cases and deaths during July - mid-Oct 2021, under various vaccination and vaccine effectiveness (VE) settings to estimate the impact of vaccination and VE for non-Delta-infection recoverees. Findings We estimate that Delta escaped immunity in 34.6% (95% CI: 0 - 64.2%) of individuals with prior wildtype infection and was 57.0% (95% CI: 37.9 - 75.6%) more infectious than wildtype SARS-CoV-2. Models assuming higher VE among those with prior non-Delta infection, particularly after the 1 st dose, generated more accurate predictions than those assuming no such increases (best-performing VE setting: 90/95% vs. 30/67% baseline for the 1 st /2 nd dose). Counterfactual modeling indicates that high vaccination coverage for 1 st vaccine-dose in India (∼50% by mid-Oct 2021) combined with the boosting of VE among recoverees averted around 60% of infections during July - mid-Oct 2021. Interpretation Non-pharmaceutical interventions, infection seasonality, and high coverage of 1-dose vaccination likely all contributed to pandemic dynamics in India during 2021. Given the shortage of COVID-19 vaccines globally and boosting of VE, for populations with high prior infection rates, prioritizing the first vaccine-dose may protect more people. Research in context Evidence before this study: We searched PubMed for studies published through Nov 3, 2021 on the Delta (B.1.617.2) SARS-CoV-2 variant that focused on three areas: 1) transmissibility [search terms: ("Delta variant" OR "B.1.617") AND ("transmission rate" OR "growth rate" OR "secondary attack rate" OR "transmissibility")]; 2) immune response ([search terms: ("Delta variant" OR "B.1.617") AND ("immune evas" OR "immune escape")]; and 3) vaccine effectiveness ([search terms: ("Delta variant" OR "B.1.617") AND ("vaccine effectiveness" OR "vaccine efficacy" OR "vaccination")]. Our search returned 256 papers, from which we read the abstracts and identified 54 relevant studies.Forty-two studies addressed immune evasion and/or vaccine effectiveness. Around half (n=19) of these studies measured the neutralizing ability of convalescent sera and/or vaccine sera against Delta and most reported some reduction (around 2-to 8-fold) compared to ancestral variants. The remainder (n=23) used field observations (often with a test-negative or cohort-design) and reported lower VE against infection but similar VE against hospitalization or death. Together, these laboratory and field observations consistently indicate that Delta can evade preexisting immunity. In addition, five studies reported higher B-cell and/or T-cell vaccine-induced immune response among recovered vaccinees than naive vaccinees, suggesting potential boosting of pre-existing immunity; however, all studies were based on small samples (n = 10 to 198 individuals).Sixteen studies examined transmissibility, including 1) laboratory experiments (n=6) showing that Delta has higher affinity to the cell receptor, fuses membranes more efficiently, and/or replicates faster than other SARS-CoV-2 variants, providing biological mechanisms for its higher transmissibility; 2) field studies (n=5) showing higher rates of breakthrough infections by Delta and/or higher viral load among Delta infections than other variants; and 3) modeling/mixed studies (n=5) using genomic or case data to estimate the growth rate or reproduction number, reporting a 60-120% increase. Only one study jointly estimated the increase in transmissibility (1.3-1.7-fold, 50% CI) and immune evasion (10-50%, 50% CI); this study also reported a 27.5% (25/91) reinfection rate by Delta.Added value of this study: We utilize observed pandemic dynamics and the differential vaccination coverage for two vaccine doses in India, where the Delta variant was first identified, to estimate the epidemiological properties of Delta and examine the impact of prior non-Delta infection on immune boosting at the population level. We estimate that Delta variant can escape immunity from prior wildtype infection roughly one-third of the time and is around 60% more infectious than wildtype SARS-CoV-2. In addition, our analysis suggests the large increase in population receiving their first vaccine dose (∼50% by end of Oct 2021) combined with the boosting effect of vaccination for non-Delta infection recoverees likely mitigated epidemic intensity in India during July - Oct 2021.Implications of all the available evidence: Our analysis reconstructs the interplay and effects of non-pharmaceutical interventions, infection seasonality, Delta variant emergence, and vaccination on COVID-19 pandemic dynamics in India. Modeling findings support prioritizing the first vaccine dose in populations with high prior infection rates, given vaccine shortages.

https://medrxiv.org/content/10.1101/2021.06.21.21259268v1.full.pdf

COVID-19 pandemic dynamics in India and impact of the SARS-CoV-2 Delta (B.1.617.2) variant

Background Our understanding of the global scale of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection remains incomplete: Routine surveillance data underestimate infection and cannot infer on population immunity; there is a predominance of asymptomatic infections, and uneven access to diagnostics. We meta-analyzed SARS-CoV-2 seroprevalence studies, standardized to those described in the World Health Organization’s Unity protocol (WHO Unity) for general population seroepidemiological studies, to estimate the extent of population infection and seropositivity to the virus 2 years into the pandemic. Methods and findings We conducted a systematic review and meta-analysis, searching MEDLINE, Embase, Web of Science, preprints, and grey literature for SARS-CoV-2 seroprevalence published between January 1, 2020 and May 20, 2022. The review protocol is registered with PROSPERO (CRD42020183634). We included general population cross-sectional and cohort studies meeting an assay quality threshold (90% sensitivity, 97% specificity; exceptions for humanitarian settings). We excluded studies with an unclear or closed population sample frame. Eligible studies—those aligned with the WHO Unity protocol—were extracted and critically appraised in duplicate, with risk of bias evaluated using a modified Joanna Briggs Institute checklist. We meta-analyzed seroprevalence by country and month, pooling to estimate regional and global seroprevalence over time; compared seroprevalence from infection to confirmed cases to estimate underascertainment; meta-analyzed differences in seroprevalence between demographic subgroups such as age and sex; and identified national factors associated with seroprevalence using meta-regression. We identified 513 full texts reporting 965 distinct seroprevalence studies (41% low- and middle-income countries [LMICs]) sampling 5,346,069 participants between January 2020 and April 2022, including 459 low/moderate risk of bias studies with national/subnational scope in further analysis. By September 2021, global SARS-CoV-2 seroprevalence from infection or vaccination was 59.2%, 95% CI [56.1% to 62.2%]. Overall seroprevalence rose steeply in 2021 due to infection in some regions (e.g., 26.6% [24.6 to 28.8] to 86.7% [84.6% to 88.5%] in Africa in December 2021) and vaccination and infection in others (e.g., 9.6% [8.3% to 11.0%] in June 2020 to 95.9% [92.6% to 97.8%] in December 2021, in European high-income countries [HICs]). After the emergence of Omicron in March 2022, infection-induced seroprevalence rose to 47.9% [41.0% to 54.9%] in Europe HIC and 33.7% [31.6% to 36.0%] in Americas HIC. In 2021 Quarter Three (July to September), median seroprevalence to cumulative incidence ratios ranged from around 2:1 in the Americas and Europe HICs to over 100:1 in Africa (LMICs). Children 0 to 9 years and adults 60+ were at lower risk of seropositivity than adults 20 to 29 (p < 0.001 and p = 0.005, respectively). In a multivariable model using prevaccination data, stringent public health and social measures were associated with lower seroprevalence (p = 0.02). The main limitations of our methodology include that some estimates were driven by certain countries or populations being overrepresented. Conclusions In this study, we observed that global seroprevalence has risen considerably over time and with regional variation; however, over one-third of the global population are seronegative to the SARS-CoV-2 virus. Our estimates of infections based on seroprevalence far exceed reported Coronavirus Disease 2019 (COVID-19) cases. Quality and standardized seroprevalence studies are essential to inform COVID-19 response, particularly in resource-limited regions.

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K Arunraj

Papers

SARS-CoV-2 seroprevalence among the general population and healthcare workers in India, December 2020-January 2021.