Wave 2 shows herd immunity to Delta variant difficult: study
The severe COVID-19 outbreak in Delhi this year has shown that the Delta variant of SARS-CoV-2 can infect people previously exposed to a different variant of the coronavirus, highlighting the challenges of achieving herd immunity against the variant, according to an international team of scientists.
The study, published Thursday in the journal Science, also found that the Delta variant was between 30 and 70% more transmissible than previous SARS-CoV-2 lines in Delhi.
Since the first case of COVID-19 was detected in Delhi in March last year, the city has experienced several outbreaks, in June, September and November 2020.
The situation worsened in April this year, when daily cases increased from around 2,000 to 20,000 between March 31 and April 16.
This has been accompanied by a rapid increase in hospitalizations and intensive care admissions, severely straining the healthcare system, with daily deaths reaching levels three times higher than previous waves.
The authors of the study noted that Delhi’s overall HIV status was 56.1%, which should confer some protection against future epidemics through herd immunity.
Herd immunity is a form of indirect protection against disease that can occur when a sufficient percentage of the population has become immune to an infection.
The latest study used genomic and epidemiological data, as well as mathematical modeling, to study the outbreak.
The work was led by the National Center of Disease Control and the Council of Scientific and Industrial Research-Institute of Genomics and Integrative Biology (CSIR-IGIB) in New Delhi with collaborators from Cambridge University and Imperial College from London, UK, and the University of Copenhagen, Denmark.
“The concept of herd immunity is essential to ending epidemics, but the situation in Delhi shows that infection with previous variants of the coronavirus will be insufficient to achieve herd immunity against Delta,” said the co-author of the study, Professor Ravi Gupta of the University of Cambridge.
“The only way to end or prevent outbreaks of Delta is to either get infected with this variant or to use booster shots that increase antibody levels enough to overcome Delta’s ability to escape the disease. neutralization, “Gupta added.
To determine whether the SARS-CoV-2 variants were responsible for the April 2021 outbreak in Delhi, the team sequenced and analyzed Delhi viral samples from the previous outbreak in November 2020 through June 2021.
They found that the 2020 outbreaks in Delhi were not linked to any variant of concern.
The Alpha variant, first identified in the UK, was only identified occasionally, mostly in foreign travelers, until January 2021, the researchers said.
Alpha rose in Delhi to around 40% of cases in March 2021, before being moved by a rapid rise in the Delta variant in April, they said.
By applying mathematical modeling to epidemiological and genomic data, the researchers found that the Delta variant was able to infect people who had previously been infected with SARS-CoV-2.
The researchers noted that a previous infection offered only 50-90% of the protection against the Delta variant infection that it provides against previous lineages.
“This work helps to understand Delta’s global epidemics, including in highly vaccinated populations, as the Delta variant can be transmitted by vaccinated or previously infected people to find those who are susceptible,” said Anurag Agrawal of CSIR-IGIB , principal author and co-principal investigator of the study.
To look for real evidence of reinfection to support their modeling work, the researchers examined a group of people recruited by CSIR.
As of February, 42.1% of unvaccinated subjects participating in the study had tested positive for antibodies against SARS-CoV-2.
In June, the corresponding number was 88.5%, suggesting very high infection rates during the second wave of the epidemic in the country.
Of the 91 subjects who had already been infected before Delta, about a quarter (27.5%) had increased levels of antibodies, which is evidence of reinfection.
When the team sequenced all vaccine discovery case samples at a single center during the study period, they found that among the 24 reported cases, Delta was seven times more likely to lead to Vaccination discovery infections than non-Delta lines.
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