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

Sheikh-Mohamed S, Chao GYC, Isho B, Zuo M, Nahass GR, Salomon-Shulman RE, Blacker G, Fazel-Zarandi M, Rathod B, Colwill K, Jamal A, Li Z, Quin de Launay K, Takaoka A, Garnham-Takaoka J, Fahim C, Paterson A, Xinliu Li A, Haq N, Barati S, Gilbert L, Green K, Mozafarihashjin M, Samaan P, Siqueira W, Mubareka S, Ostrowski M, Rini JM, Rojas OL, McGeer A, Weissman IL, Caspi Tal M, Straus S, Gingras AC, Gommerman JL.  Systemic and mucosal IgA responses are variably induced in response to SARS-CoV-2 mRNA vaccination and are associated with protection against subsequent infection. Mucosal Immunology. Apr 25 2022. Doi: 10.1038/s41385-022-00511-0

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

A paper now published in Mucosal Immunology examines whether mRNA vaccines induce antibodies in saliva. The study, partially funded by the CITF and led by University of Toronto researcher Drs. Jennifer Gommerman and Sharon Straus from Unity Health Toronto, suggests that vaccinated individuals elicit a modest immunoglobulin A (IgA) response in the saliva, but a robust immunoglobulin G (IgG) response, which mirrors what is found in blood. Low levels of serum IgA against SARS-CoV-2 in vaccinated individuals, which correlates with saliva IgA, was found to be associated with breakthrough infections. As the respiratory tract is the first site of contact for airborne pathogens such as SARS-CoV-2, the presence of protective IgA antibodies in the saliva helps in fighting off infection.

Key findings:

  • The antibody class immunoglobulin G (IgG) recognizing SARS-CoV-2 spike and receptor binding domain (RBD) were detected in the saliva of nearly all individuals after one dose of Pfizer-BioNTech or Moderna vaccines. Salivary IgG levels increased further after dose two, similar to what is observed in blood.
  • Salivary IgG levels had decreased substantially by six months following the second dose.
  • Modest levels of immunoglobulin A (IgA) – a different class of antibody that plays a big role in the immune response of the respiratory and digestive tracts – targeting spike and RBD were detected in the saliva of vaccinated individuals after one dose. However, only approximately 30% of participants had detectible salivary IgA against spike and RBD after the second dose. These findings are consistent with the fact that the currently approved COVID-19 vaccines are administered intramuscularly (i.e., injection in the arm) and not via the nasal route (such as a nasal spray), meaning the antibody response in the blood will be stronger than that in the saliva.