Reduced Covid severity in hamsters on re-infection with Delta variants: ICMR-NIV study

Re-infection with a high-virus dose of the Delta and B.1 variants three months after B.1 variant infection resulted in reduced virus shedding, disease severity and increased neutralising antibody levels in the re-infected hamsters, the researchers said. “The present findings show that prior infection could not produce sterilising immunity but that it can broaden the neutralising response and reduce disease severity in case of reinfection,” they said.

The study ‘Protective Immunity of the Primary SARS-CoV-2 Infection Reduces Disease Severity Post Re-Infection with Delta Variants in Syrian Hamsters’, was published on March 13 in ‘Viruses’.

The B.1.617.2 lineage of SARS-CoV-2 was first detected in the country on September 22, 2020. It was later categorised as a variant of concern and named the Delta variant by the WHO on May 31, 2021. The variant spread at an alarming rate to become the most dominant Covid-19 lineage circulating globally and spread to 201 countries by December 2, 2021. The amino acid substitutions in the spike protein of the Delta variant, such as D614G, T478K, P681R and L452R, are known to affect transmissibility and neutralisation.

The Delta variant has been further subdivided into Delta AY.1 and AY.127, according to the Pango lineage designation system. Among these sub-lineages, AY.1 and AY.2 possess the K417N substitution, which is also present in the B.1.351 variant, suggesting that it plays a role in immune evasion. As of December 6, 2021, the AY.1 lineage has been detected in at least 43 countries and AY.2 in eight countries.

SARS-CoV-2 generates a neutralising antibody (NAb) response after infection in humans, but the protective immune titre required to prevent subsequent infection is not yet known. In this study, researchers have studied the pathogenicity of the Delta AY.1 variant in comparison with the Delta and B.1 variants and also assessed the re-infection potential of these variants in B.1 infection-recovered hamsters three months after initial infection.