The SARS-CoV-2 virus may create a viral toxin that causes severe Covid-19 infections, a recent study published in the journal Nature Communications has cautioned even as people across the countries have dropped their guard against the pandemic.

The researchers of the study which comes in the backdrop of the WHO warning that a lethal pathogen may replace the Covid-virus, demonstrated how the SARS-CoV-2 "spike" protein can harm cell barriers that line the interior of blood veins within bodily organs like the lungs, causing what is known as a vascular leak.

One of Covid-19's deadliest symptoms, pulmonary oedema, which contributes to acute respiratory distress syndrome, may be avoided by blocking the function of this protein (ARDS). "In theory, by specifically targeting this pathway, we could block pathogenesis that leads to vascular disorder and acute respiratory distress syndrome without needing to target the virus itself," said study lead author Scott Biering, a postdoctoral scholar at the University of California, Berkeley.

"In light of all the different variants that are emerging and the difficulty in preventing infection from each one individually, it might be beneficial to focus on these triggers of pathogenesis in addition to blocking infection altogether."

While many vaccine sceptics have stoked fears about the potential dangers of the SARS-CoV-2 spike protein -- which is the target of Covid-19 mRNA vaccines -- the researchers say that their work provides no evidence that the spike protein can cause symptoms in the absence of viral infection.

Instead, their study suggests that the spike protein may work in tandem with the virus and the body's own immune response to trigger life-threatening symptoms. In addition, the amount of spike protein circulating in the body after vaccination is far less concentrated than the amounts that have been observed in patients with severe COVID-19 and that were used in the study.

"The amount of spike protein that you would have in a vaccine would never be able to cause a leak," said study senior author Eva Harris, a professor of infectious diseases and vaccinology at UC Berkeley. "In addition, there's no evidence that [the spike protein] is pathogenic by itself. The idea is that it's able to aid and abet an ongoing infection."

By examining the impact of the SARS-CoV-2 spike protein on human lung and vascular cells, and on the lungs of mice, the research team was able to uncover the molecular pathways that allow the spike protein to disrupt critical internal barriers in the body. In addition to opening new avenues for the treatment of severe COVID-19, understanding how the spike protein contributes to vascular leak could shed light on the pathology behind other emerging infectious diseases.