Variants of SARS-CoV-2, the virus causing COVID-19, are constantly emerging and will likely continue to, driven by community carriers.1 Immunity to the virus is attained through vaccination or prior infection, which produces antibodies against the SARS-CoV-2 spike protein.2 However, viral mutation is inevitable and may lead to a risk of emergence of either a more transmissible variant, or one with spike protein mutations that could help it evade immunity.2 Initially detected in November 2021, Omicron is the most recent variant to be discovered. The rapid spread of Omicron infections raises concerns, with the infections accounting for approximately 59% of all COVID-19 cases in the United States as of 25 December 2021.3 Given its high transmissibility and >30 spike protein mutations, experts believe Omicron will soon replace the Delta variant as the globally dominant SARS-CoV-2 strain.4
Current data suggests that Omicron does not predispose to more severe disease compared to the original viral strain and earlier variants.4,5 However, as observed with the Delta variant, the rapid surge in cases and increased hospitalisation rates will pose a strain on healthcare systems, possibly increasing deaths, with the unvaccinated population being most vulnerable.6 The Alpha, Beta and Delta variants continue to be of concern, with some evidence suggesting that the Alpha variant predisposes to more severe disease.7 It is thus important for us to understand effectiveness of our current vaccines against emerging variants, and the level of protection resulting from prior infections.
Ibarrondo FJ and colleagues (University of California, LA) examined serum antibodies of 10 unvaccinated individuals with prior infection (before May 2020, preceding the period when variants appeared and became prevalent in the US) and 15 vaccinated individuals without prior infection.2 The serum neutralising activity of variants with common spike mutations was measured i.e., how effectively the antibodies in these sera could sequester the virus.2 The 10 individuals with previous infection were vaccinated approximately one year following symptoms onset, and their sera were re-tested.2 Most participants in either group received two doses of either the Pfizer-BioNTech or Moderna COVID-19 vaccines.
The study showed that2:
The findings from the Ibarrondo FJ et al. study suggest that prior exposure through infection confers greater protection when combined with added antigenic exposure through vaccination.2 This also points to the importance of booster shots, as these could improve vaccination efficacy against spike variants not just in quantity or antibody titre, but also the potency of antibodies produced.2