Has the Delta variant of SARS-CoV-2 made herd immunity impossible?



Scientists hoped that, following vaccination, populations would develop herd immunity to SARS-CoV-2, reducing the risk of infection, even for people without antibodies against the virus.

However, the head of the Oxford Vaccine Group, Prof. Andrew Pollard, says herd immunity is “not a possibility” given how transmissible the Delta variant of SARS-CoV-2 is. Other health experts remain optimistic despite the challenges this rapidly spreading variant poses. Prof. Andrew Pollard, head of the Oxford Vaccine Group, says that herd immunity is “not a possibility” in light of the spread of the Delta variant of SARS-CoV-2. Prof. Pollard, who is also the chair of the Joint Committee on Vaccination and Immunisation, which advises the United Kingdom government, was giving evidence to Members of the House of Commons of the U.K. Parliament.

His comments follow the preprint publication of the latest data from the Real-time Assessment of Community Transmission 1 (REACT 1) study, which suggest that the COVID-19 vaccines are only 49% effective against the Delta variant of SARS-CoV-2. Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.

Since the outbreak of SARS-CoV-2 became a pandemic, scientists have hoped that, following an effective vaccination drive, populations could develop herd immunity to the virus.

Writing in the journal Immunity, Haley E. Randolph, a Ph.D. candidate at the University of Chicago, IL, and Dr. Luis Barreiro, an Associate Professor at Chicago, say that herd immunity describes a situation where so many individuals in a population are immune to a virus that it stops spreading and may even go into decline. As a consequence, even people who do not have an antibody response to the virus have some degree of protection.

However, scientists have been concerned that the Delta variant of SARS-CoV-2, which has been spreading in the U.K. and other countries around the world, is highly transmissible, potentially reducing the effectiveness of the COVID-19 vaccines.

Get the latest updates and research-backed information on the novel coronavirus direct to your inbox. This seems likely to be confirmed following data that academics at Imperial College London, U.K., in charge of the REACT 1 study published in a preprint form, prior to peer review. In the latest round of the study, which randomly tests up to 150,000 people in England for COVID-19, the scientists found that the Delta variant was totally dominant and that it had reduced the effectiveness of the COVID-19 vaccines to 49%.


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