Study assesses effectiveness of lactobacillus throat sprays against COVID-19

A recent study published on medRxiv* The preprint server evaluated the effectiveness of lactobacillus throat sprays against coronavirus disease 2019 (COVID-19).

Study: Evaluation of a throat spray containing lactobacilli in outpatient COVID-19 patients in a randomized, double-blind, placebo-controlled trial for symptom and viral load reduction. Image Credit: Orawan Pattaraminchai/Shutterstock


Various studies have noted the negative impact of viral respiratory illnesses, such as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections, on outpatients with unbalanced immune activation, severe inflammation, and tissue disruption. respiratory. This requires the development and implementation of therapeutic or prophylactic measures against COVID-19.

About the study

The present study investigated the clinical effectiveness of a throat spray containing Lacticaseibacillus casei AMBR2, Lactiplantibacillus plantarum WCFS1, and Lacticasibacillus rhamnosus GG versus COVID-19 in mildly symptomatic outpatients.

The team performed a double-blind, placebo-controlled clinical trial on outpatient COVID-19 patients who tested positive for the polymerase chain reaction (PCR) within 96 hours of the trial. Patients used verum spray or placebo spray for 14 days. A follow-up was carried out for a week, during which the participants answered online questionnaires.

Ten common symptoms of SARS-CoV-2 were monitored throughout the study, and summary scores for the different symptoms were compared for the verum and placebo groups. The time taken for patient symptoms to improve was assessed based on when patients reached their symptomatic tipping point.

Self-sampled throat or nose swabs were collected to perform microbiome analysis, determine SARS-CoV-2 viral loads, detect administered Lactobacillaceae strains by quantitative PCR (qPCR), and perform amplicon sequencing. The team also obtained finger prick blood samples for SARS-CoV-2 immunoglobulin G (IgG) antibody analysis.

The change in COVID-19 disease severity after treatment with the microbiome spray was the primary outcome of the study. Secondary outcomes were change in time for COVID-19 symptoms to improve, difference in SARS-CoV-2 particle levels in outpatients, change in number of specific bacterial pathogens and changing the microbiome of the nose or throat.

The study was followed by post-hoc analyzes that investigated the association between viral load and reported symptoms of COVID-19, the impact of the presence of administered strains in the human respiratory tract, and the effect of several variables on the microbiome.


The study results showed that of the 78 patients eligible for the study, 41 were randomly assigned to the verum treatment group and 37 to the placebo group. Overall, both sprays were well tolerated; however, the verum group reported an unpleasant taste and texture while the placebo group noted only the unpleasant texture of the spray. About 31% of total participants fully complied with their online questionnaires, while these online diaries were found to be complete on 20 of the 21 days of the study period. Nearly 80.5% of participants self-collected nose and throat samples, while 83.5% provided finger prick blood samples.

At the start of the study, 68% of patients reported having a cough, 70% had a runny or stuffy nose, 65% had headaches and 75% suffered from fatigue. In addition, the mean total symptom score at the same time point was 15.2 ± 9.3 in the placebo group and 13.4 ± 8.6 in the verum group. Similar symptom severities were observed in the treatment and placebo groups, while the time taken for symptoms to improve had no significant differences between the two groups with respect to total scores, pathways upper respiratory (URT), system and acute. In both groups, 59% of the total number of participants experienced symptoms 21 days after diagnosis of COVID-19, with 5% having acute symptoms, 39% having systemic symptoms, and 41% suffering from URT symptoms.

One week into the trial, 73% and 77% of the verum and placebo groups tested positive by qPCR for COVID-19, while 17% and 32% tested positive after two weeks, respectively. Additionally, at the end of the study, 6.7% of the verum group and 26% of the placebo group tested positive for SARS-CoV-2. Additionally, although a significant correlation was observed between the presence of symptoms and COVID-19 positivity, symptoms like cough and fatigue were reported even after a negative PCR result.

Analysis of finger-prick blood samples collected at the start of the study showed that approximately 6.5% of COVID-19 patients were positive or borderline positive for the presence of anti-SARS IgG -CoV-2. However, at the end of the study, almost 84% of participants had anti-SARS-CoV-2 IgG, with no significant difference observed between the verum and placebo groups.


The results of the study showed that throat sprays containing lactobacilli strains could be used effectively against COVID-19, as this method of treatment lowered respiratory viral loads and, in turn, reduced viral transmission. The researchers believed that future in-depth studies could investigate the effectiveness of this method in reducing household transmission of SARS-CoV-2 infections.

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, guide clinical practice/health-related behaviors, or treated as established information.

Sara H. Byrd