This is a summary, written by members of the CITF Secretariat, of:

Jennifer Gommerman, Omicron breakthrough infection induces superior mucosal and humoral immunity to SARS-CoV-2 variants than booster vaccination, presented at the CITF Scientific Meeting, March 8-10, 2023.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study that presented results at the CITF scientific meeting in Vancouver found that an Omicron breakthrough infection (an infection after a full vaccine series) induces a stronger overall immune response than booster vaccination alone. Both mucosal and humoral immunity contribute to the overall immune response to SARS-CoV-2. Assessing mucosal immunity involves measuring antibodies in saliva, which have been found to correlate well with antibodies found in the blood. Dr. Jennifer Gommerman (University of Toronto) led the study and presented the results.

Key findings:

  • A second mRNA vaccine dose induces a weak, transient, and variable IgA antibody response in saliva that declines in most people. In contrast, the IgG antibody response increases after the second dose.
  • People with breakthrough infections (infection after vaccination) had lower levels of serum and mucosal anti-Spike IgA.
  • Individuals with two vaccine doses and a breakthrough Omicron infection had higher neutralizing antibodiesAntibodies that bind to cell-free virus and prevent it from infecting cells against different SARS-CoV-2 variants compared to individuals with two or three vaccine doses only.
  • Omicron breakthrough infections increased anti-Spike IgG and IgA salivary antibody to Omicron.
  • Omicron breakthrough infections increased anti-Spike IgA to Wuhan SARS-CoV-2 and SARS-1.

Altogether, an Omicron breakthrough infection induces a stronger overall immune response than booster vaccination alone. It is still recommended that individuals take all the necessary precautions and continue getting booster vaccines to reduce the risk of future infections.