A new study published in The Lancet is offering the most thorough investigation to date into the increased virulence of the SARS-CoV-2 Delta variant. The research found those infected with the Delta variant were twice as likely to be hospitalized compared to those infected with prior variants, however, vaccination still effectively protected individuals from severe disease regardless of variant.
Over the last few months the rapid spread of the Delta variant has profoundly changed the course of this global pandemic. In just a few months the variant quickly became dominant, affirming just how much more infectious it is compared to prior forms of the virus. But, while it is clear Delta is more infectious it hasn’t been clear if it causes more severe disease.
The new study, peer-reviewed and published in The Lancet Infectious Diseases, investigated data from around 43,000 confirmed COVID-19 cases in the United Kingdom between March and May this year. The researchers looked at hospital admissions, comparing patients with the Delta variant to those with the previously dominant Alpha variant (also known as the UK variant).
After accounting for factors such as age and vaccination status, the study concluded those infected with the Delta variant were 2.26 times more likely to be hospitalized compared to those infected with Alpha. Including those patients who were not hospitalized but still ill enough to present to an emergency room for treatment, Delta infections were still 1.45 times higher than Alpha.
Perhaps most importantly, this increased hospitalization risk was not detected in vaccinated subjects. A striking 98 percent of all hospitalizations tracked in this study were in unvaccinated or partially vaccinated subjects. Only two percent of all hospitalizations were in fully vaccinated individuals.
"Our analysis highlights that in the absence of vaccination, any Delta outbreaks will impose a greater burden on healthcare than an Alpha epidemic,” says Anne Presanis, from the University of Cambridge and one of the lead authors on the new study. “Getting fully vaccinated is crucial for reducing an individual's risk of symptomatic infection with Delta in the first place, and, importantly, of reducing a Delta patient's risk of severe illness and hospital admission."
David Strain, a researcher from the University of Exeter, says it is not surprising to confirm the Delta variant causes more severe disease. He says it makes sense the two factors that make Delta more infectious lead to greater virulence.
This combination of more viral copies and better cellular penetration makes it more likely that the cells, tissues and organs will become overwhelmed before the immune system, particularly that of an unvaccinated individual, has had chance to mount a defence
The first factor, Strain explains, is Delta’s ability to replicate more rapidly in the early phases of infection. The means alongside greater transmission to others it can also spread more swiftly through a human body. The second part of Delta’s mutated toolkit is a spike protein modification allowing it to penetrate cells faster.
“This combination of more viral copies and better cellular penetration makes it more likely that the cells, tissues and organs will become overwhelmed before the immune system, particularly that of an unvaccinated individual, has had chance to mount a defence,” says Strain, who did not work on this new study.
A previous study from the same UK research team tracked COVID-19 cases between November and January to quantify the severity of the Alpha variant. That research found Alpha cases were 52 percent more likely to be hospitalized compared to the original strain of SARS-CoV-2.
While these new findings are a pertinent reminder of the importance of vaccination in protecting one from severe, COVID-19 the study is also a worrisome portent of the danger unvaccinated countries face from the Delta variant. A commentary on the new study by researchers Jerome Lechien and Sven Saussez argues these findings should add urgency to global vaccination efforts.
“The most important finding from Twohig and colleagues' study is that outbreaks of the Delta variant in unvaccinated populations might lead to a greater burden on health-care services than the Alpha variant,” writes Lechien and Saussez. “This information is important for future decision making, providing additional arguments to strengthen vaccination programmes worldwide before the spread of a new variant with resistance to the vaccines.”
The new study was published in the journal The Lancet Infectious Diseases.
Source: University of Cambridge