Vaccinated immune system response to new SARS-CoV-2 variants

A/Prof Menno van Zelm in the lab

Associate Professor Menno van Zelm was invited by the prestigious journal Science Immunology to write a Commentary on two papers that deal with immune memory after vaccination and recognition of Omicron variants of SARS-CoV-2. 

A/Prof van Zelm said, "What I suggest is that 'original antigenic sin' - that means that the body's original response to an antigen is remembered and used when a variant antigen is encountered - might be in place, so that it will be a challenge for the immune system to generate new responses on top of the existing (vaccine-induced) memory."

In the commentary, A/Prof van Zelm discusses two recent publications in Science Immunology by Quandt et al. and Kaku et al. that both evaluate the vaccine-induced antibody response in double- or triple-dose mRNA-vaccinated individuals (Pfizer or Moderna). 

Both demonstrate that antibody amounts decline between one and six months after the second dose but are boosted by the third dose. Importantly, A/Prof van Zelm says, the relative recognition of variants of concern (VoC) is strongly boosted, demonstrating an improved capacity for protection including against Omicron. 

However, he says, both show also that immune memory to other Omicron variants (BA.2 and BA.4/BA.5) are lower. "Interestingly, a breakthrough infection with Omicron BA.1 after double-dose vaccination showed similar degrees of immune memory boosting, also with reduced recognition of other omicron variants. 

"Furthermore, all immune memory after Omicron breakthrough infection also recognised the original Wuhan strain with high affinity, thus showing that the breakthrough infection only boosted previous vaccine-induced memory. Thus, no new memory was formed that responded specifically to Omicron."

In summary, A/Prof van Zelm says, "The good news is that the current vaccine still works and booster doses improve immune memory, also to Omicron.

"The potential bad news is that changing the vaccine to a variant, e.g. Omicron, might not have additional boosting effects to protect against variant forms of SARS-CoV-2. This is at least what the current data suggest, but more studies and longer follow-up in recovered individuals are needed to draw a firm conclusion."
 
A/Prof Menno C. van Zelm is Head, Laboratory for Allergy and Clinical Immunology, Deputy Head (Research) Dept. Immunology and Pathology and Chair Nomenclature Committee International Union of Immunological Societies (IUIS).

Reference
van Zelm MC. Immune memory to SARS-CoV-2 Omicron BA.1 breakthrough infections: To change the vaccine or not? Sci Immunol. 2022 Jun 2:eabq5901. doi: 10.1126/sciimmunol.abq5901.