Limosilactobacillus reuteri DSM 17938 supplementation and SARS-CoV-2 specific antibody response in healthy adults: a randomized, triple-blinded, placebo-controlled trial

Abstract

Studies have shown that probiotics can decrease the symptoms of respiratory tract infections as well as increase antibody responses following certain vaccinations. We examined the effect of probiotic supplementation on anti-SARS-CoV-2 specific antibody responses upon SARS-CoV-2 infection as well as after COVID-19 vaccination. In this randomized, triple-blinded, placebo-controlled intervention study with a parallel design, 159 healthy adults without prior SARS-CoV-2 infection or COVID-19 vaccination and any known risk factors for severe COVID-19 were randomly allocated into two study arms. The active treatment arm consumed a probiotic product containing a minimum of 1 × 10⁸ colony-forming units of Limosilactobacillus reuteri DSM 17938 + 10 μg vitamin D3 twice daily for 6 months. The placebo arm consumed identical tablets containing only 10 μg vitamin D3. Anti-SARS-CoV-2 specific antibodies and virus neutralizing antibody titers were analyzed from blood samples collected at baseline, after 3 months, and after 6 months. Differences in serum antibody titers between the two study arms were tested with independent t-test using log-transformed values. In the intention-to-treat (ITT) analysis, SARS-CoV-2 infected individuals in the active treatment arm (n = 6) tended to have higher serum anti-spike IgG (609 [168-1480] BAU/ml vs 111 [36.1-1210] BAU/ml, p = 0.080) and anti-receptor binding domain (RBD) IgG (928 [212-3449] BAU/ml vs (83.7 [22.8-2094] BAU/ml, p = 0.066) levels than individuals in the placebo arm (n = 6). Considering individuals who were fully vaccinated with mRNA-based COVID-19 vaccines, the active treatment arm (n = 10) exhibited significantly higher serum levels of anti-RBD IgA (135 [32.9-976] BAU/ml vs 61.3 [26.7-97.1] BAU/ml, p = 0.036) than the placebo arm (n = 7) >28 days postvaccination. Supplementation with specific probiotics might improve the long-term efficacy of mRNA-based COVID-19 vaccines via enhanced IgA response.

Keywords: COVID-19; Probiotics; SARS-CoV-2; antibody; immunology.

Figure 1.

Flowchart showing the number of study participants from the start of the trial to the analyzed populations. ITT=Intention-to-treat, PP=Per-protocol.

Figure 2.

Serum anti-SARS-CoV-2 specific antibody (a-f) and virus-neutralizing antibody levels (g) in study participants who were infected during the study period (intention-to-treat population). S = spike, RBD = receptor-binding domain, N = nucleocapsin, nAB = neutralizing antibody. Statistical comparisons between the groups were performed with independent t-test using log-transformed values except nAB titers which were compared with non-parametric Mann-Whitney test. The bar plots show median, and the dots represent individual values within the group.

Figure 3.

Serum anti-SARS-CoV-2 specific antibody (a-d) and virus-neutralizing antibody levels (e) in study participants who received two vaccine doses during the study period (intention-to-treat population). S = spike, RBD = receptor-binding domain, nAB = neutralizing antibody. Statistical comparisons between the groups were performed with independent t-test using log-transformed values except nAB titers which were compared with non-parametric Mann-Whitney test. The bar plots show median, and the dots represent individual values within the group.

Figure 4.

Serum anti-SARS-CoV-2 specific antibody (a-d) and virus-neutralizing antibody (e) levels in study participants who received two vaccine doses during the study period and were sampled more than 14 days after the second dose (intention-to-treat population). The red dots represent individuals who were either partly or fully vaccinated with the Astra-Zeneca’s AZD1222 vaccine. S = spike, RBD = receptor-binding domain, nAB = neutralizing antibody. Statistical comparisons between the groups were performed with independent t-test using log-transformed values except nAB titers which were compared with non-parametric Mann-Whitney test. Black p-values refer to the whole population and red p-values to the population who received only Pfizer-BioNTech’s BNT162b2 vaccine or Moderna’s mRNA-1273 vaccine. The bar plots show median, and the dots represent individual values within the group.

Figure 5.

Serum anti-SARS-CoV-2 specific (a-d) and virus-neutralizing (e) antibody levels in study participants who received two vaccine doses during the study period and were sampled more than 28 days after the second dose (intention-to-treat population). The red dots represent individuals who were either partly or fully vaccinated with the Astra-Zeneca’s AZD1222 vaccine. S = spike, RBD = receptor-binding domain, nAB = neutralizing antibody. Statistical comparisons between the groups were performed with independent t-test using log-transformed values except nAB titers which were compared with non-parametric Mann-Whitney test. Black p-values refer to the whole population and red p-values to the population who received only Pfizer-BioNTech’s BNT162b2 vaccine or Moderna’s mRNA-1273 vaccine. The bar plots show median, and the dots represent individual values within the group.

Figure 6.

Study design.