High-quality studies suggest that the Lactobacillus rhamnosus, LGG^®, Lactobacillus paracasei, L. CASEI 431^® and Bifidobacterium, BB-12^® strains (hereafter referred to by use of the trademarks LGG^®, L.CASEI 431^® and BB-12^®) may support the immune system, and are associated with reduced incidence, duration and severity of flu-like symptoms and flu-like sickness in children and adults.^{1, 2, 3, 4, 5} 

Respiratory and flu-like sickness 

Probiotics may help a healthy immune system

The L. CASEI 431^®, BB-12^® and LGG^® strains have all been studied in high-quality clinical studies. In children and adults, supplementing with these strains has been associated with a promotion of the immune system and may lower incidence of respiratory and flu-like sickness.^{1, 2, 3, 4, 5, 8, 9, 10}

But how do we know how strong our immune system is? 

Studies suggest that LGG^® may help promote the immune system and may help reduce the incidence of flu-like symptoms

A study of healthy adults investigated how supplementing with the LGG^® strain affected the number of antibodies the body produced in response to a vaccine challenge.⁹ Compared to taking placebo, 29% more participants who took LGG^® produced a number of specific antibodies that is associated with increased immune system function. This suggests that the LGG^® strain may help promote immune responses by increasing the number of antibodies the body makes to fight against foreign invaders.⁹  

In another study, children who consumed the LGG^® probiotic strain for three months had a significant reduction in the incidence of flu-like sickness.¹ The length of time that children experienced symptoms was also reduced, and they had significantly fewer days away from daycare due to illness, compared to the placebo group.¹ Similarly, children who consumed LGG^® for the length of a hospital stay had a significantly lower incidence of digestive system illness and flu-like sickness.¹⁰  

Studies suggest that BB-12^® may help support the immune system and reduces the incidence of certain types of illness 

L. CASEI 431^® may help promote good health

Several studies have associated the L. CASEI 431^® probiotic strain with a healthier immune system response to vaccine challenges. Three high-quality studies administered the L. CASEI 431^® strain to healthy adults prior to a vaccine challenge. In all three studies, the group supplemented with the L. CASEI 431^® probiotic strain had an increase in specific antibodies associated with the vaccine challenge compared to the placebo group.^{2, 3, 4} 

In a large study, 1104 volunteers received the L. CASEI 431^® strain or placebo for 42 days. In those who received L. CASEI 431^®, the duration of flu-like illness was significantly reduced compared to placebo.⁸

LGG^®, L. CASEI^® and BB-12^® may play an important role in how the immune system supports our health

These high-quality clinical studies have associated the LGG^®, L. CASEI^® and BB-12^® probiotic strains with a promotion of the immune system and support the way it responds when confronted with an immune challenge that could affect our health. Additionally, clinical studies show that the probiotic strains are associated with a reduced incidence, risk, duration and severity of respiratory and flu-like sickness.  
Read what to look for when choosing a probiotic. 

L. CASEI^®, LGG^® and BB-12^® are registered trademarks of Chr. Hansen A/S. 

Reference list

References
1. Hojsak I, et al. Lactobacillus GG in the prevention of gastrointestinal and respiratory tract infections in children who attend day care centers: a randomized, double-blind, placebo-controlled trial. Clin Nutr. 2010;29(3):312-6. (PubMed)
2. Rizzardini G, et al. Evaluation of the immune benefits of two probiotic strains Bifidobacterium animalis ssp. lactis, BB-12^® and Lactobacillus paracasei ssp. paracasei, L. casei 431^® in an influenza vaccination model: a randomised, double-blind, placebo-controlled study. Br J Nutr. 2012;107(6):876-84. (PubMed)
3. Trachootham D, et al. Drinking fermented milk containing Lactobacillus paracasei 431 (IMULUS^™) improves immune response against H1N1 and cross-reactive H3N2 viruses after influenza vaccination: A pilot randomized triple-blinded placebo controlled trial. J Funct Foods. 2017;33:1-10. (Source)
4. de Vrese M, et al. Probiotic bacteria stimulate virus-specific neutralizing antibodies following a booster polio vaccination. Eur J Nutr. 2005;44(7):406-13. (PubMed)
5. Smith TJ, et al. Effect of Lactobacillus rhamnosus LGG^® and Bifidobacterium animalis ssp. lactis BB-12^® on health-related quality of life in college students affected by upper respiratory infections. The British journal of nutrition. 2013;109(11):1999-2007. (PubMed)
6. Biggerstaff M, et al. Systematic Assessment of Multiple Routine and Near Real-Time Indicators to Classify the Severity of Influenza Seasons and Pandemics in the United States, 2003-2004 Through 2015-2016. Am J Epidemiol. 2018;187(5):1040-50. (PubMed)
7. Putri WCWS, et al. Economic burden of seasonal influenza in the United States. Vaccine. 2018;36(27):3960-6. (PubMed)
8. Jespersen L, et al. Effect of Lactobacillus paracasei subsp. paracasei, L. casei 431 on immune response to influenza vaccination and upper respiratory tract infections in healthy adult volunteers: a randomized, double-blind, placebo-controlled, parallel-group study. Am J Clin Nutr. 2015;101(6):1188-96. (PubMed)
9. Davidson LE, et al. Lactobacillus GG as an immune adjuvant for live-attenuated influenza vaccine in healthy adults: a randomized double-blind placebo-controlled trial. Eur J Clin Nutr. 2011;65(4):501-7. (PubMed)
10. Hojsak I, et al. Lactobacillus GG in the prevention of nosocomial gastrointestinal and respiratory tract infections. Pediatrics. 2010;125(5):e1171-7. (PubMed)