Immune Imprinting Risk Following COVID-19 Vaccination Reported

The World Health Organization (WHO) today announced that in vitro evidence shows that immune imprinting occurs with repeated exposure to the same antigen from COVID-19 vaccines.

Also known as original antigenic sin, immune imprinting is a phenomenon in which immune memory recall biases the immune response towards previously encountered antigens.

However, the clinical impact of immune imprinting in observational epidemiological studies to date is unclear due to limited data and the possibility of bias reported by the WHO's Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) on April 14, 2023.

Additionally, the TAG-CO-VAC concluded:

Booster doses of index virus-based vaccines continue to confer high levels of protection against severe disease and death caused by all SARS-CoV-2 variants, including contemporary Omicron descendent lineages.

Protection from severe disease and symptomatic infection induced by index virus-based vaccines and BA.1- or BA.4/5-containing bivalent mRNA vaccines declines over time. However, protection from severe disease is maintained longer than protection from symptomatic infection.

Compared to index virus-based vaccines, booster doses of BA.1- or BA.4/5-containing bivalent mRNA vaccines may modestly increase vaccine effectiveness against symptomatic disease. At the same time, the small number of studies assessing severe outcomes show similar results estimates of vaccine effectiveness.

Both BA.1- and BA.4/5-containing bivalent mRNA vaccines enhance the magnitude and elicit a greater breadth of cross-reactive immune responses to SARS-CoV-2 variants when used as a booster dose, as compared to the index virus-based vaccines.

BA.4/5-containing bivalent mRNA vaccines induced higher neutralizing antibody titres against recent descendent lineages of Omicron (BQ.1, XBB.1) compared to BA.1-containing bivalent mRNA vaccines when used as a booster dose.

The role of the TAG-CO-VAC is to recommend whether updates to vaccine composition are needed so that they continue to protect against SARS-CoV-2 variants safely.

WHO recommendations on vaccination policies are issued by the Strategic Advisory Group of Experts on Immunization (SAGE). 

The latest SAGE recommendations on COVID-19 boosters can be found at this link.