It is known that existing COVID-19 vaccines trigger the production of neutralizing antibodies in blood. However, since SARS-CoV-2 first enters the body via the upper respiratory tract, if antibodies were located in this area, they could potentially start fighting the virus immediately. A recent preprint, not yet peer-reviewed, examines whether COVID-19 vaccines induce antibodies in saliva. The study, partially funded by the CITF and led by University of Toronto researcher Jennifer Gommerman, suggests that there is a modest neutralizing capacity in the saliva of vaccinated individuals – which may contribute to reducing transmission of SARS-CoV-2.

Researchers analyzed antibodies against the SARS-CoV-2 Spike (S) and its receptor binding domain (RBD) in the saliva of people who had recovered from COVID-19 or who had received any of the approved COVID-19 vaccines.

When analyzing samples from people who had had two doses of an mRNA vaccine (Pfizer-BioNTech or Moderna), the authors observed that:

  • IgG antibodies Immunoglobulin G (IgG) is the most common type of antibody found circulating in blood (representing approximately 75% of antibodies found in blood). recognizing S were detected in the saliva after dose 1 and increased further after dose 2; this is similar to what is often observed in blood with the systemic immune response.
  • Levels of IgG antibodies against the SARS-CoV-2 S protein in the saliva were comparable between people who recovered from COVID-19 and people who received two doses of an mRNA vaccine.
  • Soluble IgA antibodies Immunoglobulin A (IgA, also referred to as sIgA in its secretory or soluble form) it can be found bound to cells or soluble; in blood, saliva, tears, respiratory and gastric secretions, and breast milk. It represents up to 15% of total antibodies produced throughout the body. in saliva (sIgA) recognizing S or RBD were detected in nearly all vaccinated participants after one dose of the mRNA vaccines, but diminished after dose 2.

When analyzing samples from people who had had a first dose of the Oxford-AstraZeneca adenovirus vaccine (Ad) followed by a second dose of either of the mRNA vaccines, similar levels of anti-S/RBD IgG and IgA were found in saliva when compared to two doses of an mRNA vaccine. All vaccine combination regimes (mRNA/mRNA or Ad/mRNA) nevertheless triggered a modest neutralizing capacity in saliva.

The authors conclude that SARS-CoV-2 mRNA/mRNA and Ad/mRNA vaccination induces antibodies in saliva, but that the antigen-specific sIgA response is compartmentalized (found in certain fluids, with limited presence in the blood), transient (thus, cannot be boosted with a second dose) and does not equate to systemic immunity (i.e., other layers of immunity may be present despite the waning of antibodies in the saliva). Therefore, although the vaccine-induced antibodies found in saliva may not be enough to neutralize the virus, they may contribute to reducing person-to-person transmission of SARS-CoV-2.

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. A mucosal antibody response is induced by intra-muscular SARS-CoV-2 mRNA vaccination. medRxiv 2021.08.01.21261297; doi: https://doi.org/10.1101/2021.08.01.21261297