PMID: 35815463

In early 2020, a global emergency was upon us in the form of the coronavirus disease 2019 (COVID-19) pandemic. While horrific in its health, social and economic devastation, one silver lining to this crisis has been a rapid mobilization of cross-institute, and even cross-country teams that shared common goals of learning as much as we could as quickly as possible about the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and how the immune system would respond to both the virus and COVID-19 vaccines. Many of these teams were formed by women who quickly realized that the classical model of "publish first at all costs" was maladaptive for the circumstances and needed to be supplanted by a more collaborative solution-focused approach. This review is an example of a collaboration that unfolded in separate countries, first Canada and the United States, and then also Israel. Not only did the collaboration allow us to cross-validate our results using different hands/techniques/samples, but it also took advantage of different vaccine types and schedules that were rolled out in our respective home countries. The result of this collaboration was a new understanding of how mucosal immunity to SARS-CoV-2 infection vs COVID-19 vaccination can be measured using saliva as a biofluid, what types of vaccines are best able to induce (limited) mucosal immunity, and what are potential correlates of protection against breakthrough infection. In this review, we will share what we have learned about the mucosal immune response to SARS-CoV-2 and to COVID-19 vaccines and provide a perspective on what may be required for next-generation pan-sarbecoronavirus vaccine approaches.

PMID: 35468942

Although SARS-CoV-2 infects the upper respiratory tract, we know little about the amount, type, and kinetics of antibodies (Ab) generated in the oral cavity in response to COVID-19 vaccination. We collected serum and saliva samples from participants receiving two doses of mRNA COVID-19 vaccines and measured the level of anti-SARS-CoV-2 Ab. We detected anti-Spike and anti-Receptor Binding Domain (RBD) IgG and IgA, as well as anti-Spike/RBD associated secretory component in the saliva of most participants after dose 1. Administration of a second dose of mRNA boosted the IgG but not the IgA response, with only 30% of participants remaining positive for IgA at this timepoint. At 6 months post-dose 2, these participants exhibited diminished anti-Spike/RBD IgG levels, although secretory component-associated anti-Spike Ab were more stable. Examining two prospective cohorts we found that participants who experienced breakthrough infections with SARS-CoV-2 variants had lower levels of vaccine-induced serum anti-Spike/RBD IgA at 2-4 weeks post-dose 2 compared to participants who did not experience an infection, whereas IgG levels were comparable between groups. These data suggest that COVID-19 vaccines that elicit a durable IgA response may have utility in preventing infection. Our study finds that a local secretory component-associated IgA response is induced by COVID-19 mRNA vaccination that persists in some, but not all participants. The serum and saliva IgA response modestly correlate at 2-4 weeks post-dose 2. Of note, levels of anti-Spike serum IgA (but not IgG) at this timepoint are lower in participants who subsequently become infected with SARS-CoV-2. As new surges of SARS-CoV-2 variants arise, developing COVID-19 booster shots that provoke high levels of IgA has the potential to reduce person-to-person transmission.

DOI: 10.1101/2021.08.22.21262168

Vaccination induced antibody and T-cell immune responses are important for systemic protection from COVID-19. Because SARS-CoV-2 infects and is transmitted by oral-pharyngeal mucosa, we wished to test mucosal antibodies elicited by natural infection or intramuscular vaccine injection. In a non-randomized observational study, we measured antibodies against the SARS-CoV-2 RBD in plasma and saliva from convalescent or vaccinated individuals and tested their neutralizing potential using a replication competent rVSV-eGFP-SARS-CoV-2. We found IgG and IgA anti-RBD antibodies as well as neutralizing activity in convalescent plasma and saliva. Two doses of mRNA vaccination (BNT162b2 or mRNA-1273) induced high levels of IgG anti-RBD in saliva, a subset of whom also had IgA, and significant neutralizing activity. We detected anti-RBD IgG and IgA with significant neutralizing potential in the plasma of single dose Ad26.COV2.S vaccinated individuals, and we detected slight amounts of anti-RBD antibodies in matched saliva. The role of salivary antibodies in protection against SARS-CoV-2 infection is unknown and merits further investigation. This study was not designed to, nor did it study the full kinetics of the antibody response or protection from infection, nor did it address variants of SARS-CoV-2.