Laboratory research from South Africa strongly suggests that the SARS-CoV-2 Omicron variant escapes antibody immunity induced by the Pfizer-BioNTech (Comirnaty) vaccine, but that considerable immunity is retained in people who were both vaccinated and previously infected.

The research, led by Professor Alex Sigal from the Africa Health Research Institute (AHRI), has been accepted for publication in Nature and is available as an advance article preview here.

The research confirms predictions that the large number of mutations in the spike protein and elsewhere on the Omicron variant would translate into some evasion of the immune response induced by current vaccines. It also shows that Omicron – despite its many mutations – still requires binding to the angiotensin-converting enzyme 2 (ACE2 ‘receptor’) in order to infect cells.

For this work Sigal’s team used plasma, which is a blood product which contains antibodies, from 12 vaccinated people and added either live Omicron or live ancestral (original) SARS-CoV-2 virus. The ability of the antibodies in the plasma to control the two viruses was compared – a so-called ‘neutralisation’ test. They found that there is an extensive, 40-fold decrease in the ability of antibodies from the Pfizer-BioNTech vaccine to neutralise the Omicron variant, compared with the ancestral virus. However, the plasma of those who had both been vaccinated and had a previous infection show relatively high neutralisation against Omicron.

“This was better than I expected of Omicron,” said Sigal. “The virus is so changed, there was concern that it uses a different receptor, not ACE2. If that were the case, many of our pharmacological tools to control this virus would become useless. But this is not the case. Instead, previous infection, followed by vaccination – or likely a booster – is probably protective against Omicron, and almost certainly against severe disease. So, Omicron is a tractable problem with the tools that we have already got.”

“The clinical implications of these important laboratory data need to be determined. It is likely that less vaccine-induced protection against infection and disease would be the result. Importantly, most vaccinologists agree that the current vaccines will still protect against severe disease and death in the face of Omicron infection. It is therefore critical that everyone should be vaccinated,” said AHRI executive director Professor Willem Hanekom.

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Top figure: Neutralization of the Omicron virus compared to D614G ancestral virus participants vaccinated with BNT162b2 and infected by ancestral SARSCoV-2 (green) or vaccinated only. 14 samples from 12 participants were tested. Red horizontal line denotes most concentrated plasma tested. Numbers in black above each virus strain are geometric mean titers (GMT) of the reciprocal plasma dilution (FRNT50) causing 50% reduction in the number of infection foci. Number in red denote fold-change in GMT between virus strain on the left and the virus strain on the right of each panel. p=0.0018 as determined by the Wilcoxon rank sum test.