Post-COVID-19 pandemic increased incidence of invasive bacterial infections: potential links with altered herd trained immunity.

Abstract

There has been a global increase in the incidence of various infectious diseases observed since the end of the COVID-19 pandemic. It could be hypothesized that this increase results from two independent phenomena. One is related to impaired immunity of long Covid patients. The second, the major, is associated with the long-term isolation of many people during the global pandemic lockdown resulting in an extreme reduction of contact with natural environmental human microbiota. This, in turn, led to a silencing state of the body's defense systems, including a decline of the pre-pandemic trained immunity (innate memory) that persists only for weeks to months after exposure. This decrease in trained immunity may be especially important for morbidity of infectious diseases without currently available vaccines, such as invasive Group A Streptococcus pyogenes (GAS) infections, primarily streptococcal toxic shock syndrome (STSS). This review discusses the data that support the important role of trained macrophages in host defense and demonstrates the potential clinical implications of β-glucan, the major inducer of trained macrophages, for prophylactic and therapeutic use in a case of impaired personal innate immunity. Altogether, it might be speculated that trained innate immunity within an entire population can lead to the development of Herd Trained Immunity, the novel coined the medical term. HTI can supplement classical antigen-specific herd immunity (memory B and T cells) and plays a key role in preventing various infectious diseases, including invasive GAS infections. Unfortunately, the global HTI has been overthrown during the COVID-19 pandemic but it should be restored shortly.