Infection controls should stay in place in the current post-vaccine era and there is ‘an urgent need’ to find ways to boost vaccination responses against Covid-19 variants.
This is according to researchers from the University of Cambridge who found vaccinated health care workers infected with the Delta variant pose a significant risk to patients who have a poor immune response to the vaccine.
Through lab-based experiments and epidemiological studies, their work highlights the increased infectivity of the Delta variant. The variant evades the immune response because it is better at replicating and spreading than other variants. Their findings were published this week in the journal Nature.
The Delta variant was first discovered in India in late 2020 and spread quickly to over 90 different countries. It is currently the dominant variant in the UK and is responsible for nearly all new cases of coronavirus infection.
Professor Ravi Gupta from the University of Cambridge, one of the study’s senior authors, said: ‘We’ve shown that the Delta variant is better at replicating and spreading than other commonly-observed variants. There’s also evidence that neutralising antibodies produced as a result of previous infection or vaccination are less effective at stopping this variant.’
The team extracted serum from blood samples of people who had been infected with Covid-19 or vaccinated with either the Oxford/AstraZeneca or Pfizer. These samples were part of the Covid-19 cohort of the NIHR BioResource.
The Delta variant was nearly six-fold less sensitive to the sera from previously infected individuals, and as much as eight-fold less sensitive to vaccine sera when compared with the Alpha variant. This means it would take eight times as many antibodies from a vaccinated individual to block the virus.
In addition, the researchers analysed over one hundred infected healthcare workers at three Delhi hospitals, nearly all of whom had been vaccinated against Covid-19 and found that the Delta variant was transmitted between vaccinated staff to a greater extent than the Alpha variant.
Professor Anurag Agrawal from the CSIR Institute of Genomics and Integrative Biology, Delhi, India and joint senior author, added: ‘Infection of vaccinated healthcare workers with the Delta variant is a significant problem. Although they themselves may only experience mild Covid, they risk infecting individuals who have suboptimal immune responses to vaccination due to underlying health conditions – and these patients could then be at risk of severe disease.’
He added: ‘We urgently need to consider ways of boosting vaccine responses against variants among healthcare workers. It also suggests infection control measures will need to continue in the post-vaccine era.’