likely, residual infection. 3 Not only has the morbidity of this disease stressed patients, families, and underprepared healthcare systems, but it also has the potential to enact long-term, fundamental change in daily life for billions of people. 4 The observed morbidity of COVID- 19 will be further magnified in vulnerable populations: namely the elderly, patients with cancer undergoing treatment, patients of low socioeconomic status with poor access to care and chronic conditions, as well as in countries in which health system preparedness is lacking and where the economic impacts might be devasting. [5] [6] [7] [8] Successful management of this pandemic requires: containment, therapies to reduce clinical morbidity and mortality, and ultimately, vaccination to prevent infection. Currently, multiple therapeutic agents are being evaluated to lessen the clinical morbidity of COVID-19 with varying degrees of success. 9 These include anti-malarial medications, 10 antiviral medications, 11 and convalescent serum harvested from patients recovered from the infection. 12 The rational development of a vaccine is of paramount importance. 13 New vaccine development, however, will take time, trial, and error and must be developed and distributed on a global scale. [14] [15] [16] The bacillus Calmette-Guerin (BCG) vaccine has been administered for the prevention of tuberculosis (TB) in many countries worldwide to almost four billion persons since its first human use was described in 1921. 17 The BCG vaccine provides protection from TB infection in 40- 60% of recipients and has demonstrated relative safety with a rate of serious adverse events approaching zero. 18 In both animal and human studies, BCG vaccination provides a non-specific benefit to the immune system, relative protection against, and reduced mortality from infections by other microbes (bacteria and viruses) which may occur by epigenetic reprogramming and induction of trained immunity. 19, 20 Bacillus Calmette-Guerin is a well-known medication to urologists as it is administered intravesically as therapy for many patients with non-muscle invasive bladder cancer (NMIBC). Emerging evidence suggests that BCG vaccination might reduce the rate of infection and mitigate the rate of mortality in countries with BCG vaccination programs. 21 Herein, we review the current literature regarding BCG vaccination and COVID-19, currently enrolling clinical trials, and the potential to leverage the expertise of the urologist and the urology clinic in supporting these trials.
Clinical trials have shown that BCG immunotherapy prevents cancer recurrence, progression, reduces the need for cystectomy, and prolongs survival for patients with NMIBC. 22 For intravesical therapy, the schedule of BCG treatment comprises an induction course (6 weekly treatments) and a maintenance courses of three instillations spaced one
week apart, at 3 and 6 months after induction and then every 6 months thereafter, for a total of seven sets of maintenance. Thus, a complete treatment of induction and maintenance adds up to 27 instillations over 3 years. 23 Since BCG is a live, attenuated mycobacterium, it must be handled appropriately. Urologic clinics, pharmacists, and nurses are familiar with the safe preparation, handling, and disposal of BCG.
Over 95% of treated patients have no significant toxicity, however, serious and even fatal toxicity can occur if BCG is not administered appropriately. Because of the sheer number of installations per patients, urologists are experienced in caring for patients with complications of BCG instillation and, should such complications occur with BCG vaccination, may be uniquely positioned to manage such complications. The SWOG PRIME trial evaluating priming patients with subcutaneous BCG 3 weeks prior to intravesical BCG is ongoing. This trial was somewhat prescient since, while urologists do not routinely perform BCG vaccination, trial sites will have additional expertise with vaccine administration. 24 There are reasonable concerns about allocation of BCG for COVID-19 given the shortages of both the intravesical and vaccination formulations worldwide. 25, 26 When Kamat and colleagues were designing the BADAS study in early March, they reached out to the bladder cancer patient community and Bladder Cancer Advocacy Network (BCAN), for input and support for diversion of some of the drug (BCG) to the study.
As always, the patients and BCAN were altruistic and supportive.
Additionally, some consider BCG as a class I-II pathogen and it is recommended that it be reconstituted in a certified biological cabinet and used within 2 hours per the manufacturer's label. 26 Recently, we presented evidence for TICE® BCG (Merck, Kenilworth, NJ) that BCG organisms remain viable for at least 8 hours after reconstitution when stored on ice and in the absence of light. 27 Additional support for a longer duration of viability was demonstrated for at least 4 hours, 28 and guidance from the World Health Organization (WHO) on administration of BCG vaccination for TB suggests that the vaccine may be administered up to 6 hours after reconstitution. 29 Such considerations are important as one vial of BCG is used for one patient with bladder cancer but can be used to inoculate 500 individuals for vaccination (which is 1/500th the dose, based on CFU). In order to deliver 500 doses from one vial within 2 hours, 4.2 vaccines would need to be administered every minute. For clinical trials, extending BCG reconstitution time may be important to ensure that vaccine is not wasted in times of shortage for either bladder cancer patients or TB vaccination. 30 
Members of our group recently also described differences in the observed crude case fatality rates (CFR) of COVID-19 between countries with active BCG vaccination programs for tuberculosis when compared to those that do not routinely vaccinate. 21 Starting from data extrapolated from March 22, 2020, the daily incidence of COVID-19 was 0.8/million in countries with a BCG vaccination program compared to nearly 34.8/million in countries without such a program (Table 1 ). There was considerable observational overlap between the countries without an active BCG vaccination program and those that are most affected by COVID-19 in Europe, with CFR estimates around 4.1% in countries with a BCG vaccination program compared to 5.1% in those without. These analyses may in part be explained by numerous confounding factors, including heterogeneity, likely lower testing rates within these countries, the lack of a confirmation of true BCG vaccination status among those affected, and an underestimation of asymptomatic cases, but highlight the need for further study.
The World Health Organization (WHO) acknowledges the potential bias of the aforementioned ecological study and recommends studying the potential impact of BCG on COVID-19 in clinical trials, such as the BADAS trial (www.bcgba das.org), rather than simply recommending BCG vaccination to all, as is being done in some countries. 31 Given BCG supply shortages for both intravesical and vaccine formulations, the WHO additionally cautions that overuse of the BCG vaccine for COVID-19 prevention without additional, prospective data may prove harmful.
Evidence supports the immunomodulatory potential of BCG administration. Neonatal BCG vaccination has been associated with a 50% reduction in neonatal mortality in developing nations, with vaccinated infants having fewer cases of respiratory infections and sepsis. 32 Arts and colleagues were able to demonstrate additional heterologous benefits of BCG vaccination by performing a randomized controlled study in which 30 healthy Dutch men received either placebo or BCG (Denmark strain), following which all participants received yellow fever vaccination after 30 days. 19 Participants who had received BCG vaccination were found to have a reduction in yellow fever viremia. Furthermore, in this study, when the participants were BCG vaccinated and then later challenged with yellow fever virus, they had decreased "cytokine storm," -IFNa, IFNg, IL1Ra, IL8, and TNF all decreased. 19 This would be expected because it is well known that BCG stimulates a TH1 response; whereas, yellow fever (and most likely COVID-19) stimulates at TH2 response. Tipping the response one way or the other usually mitigates the other response, so it is not surprising that a TH1 stimulant reduces a TH2 response. This is particularly of in- vaccine strain compared to placebo-treated participants, with increased production of IFN-y and IL-6. 33 The reasons for this variability in response mechanisms governing these findings are not known. (NCT04350931). The ultimate goal of all these studies is to inform the decision to use BCG as a vaccine for all individuals at high risk of exposure, for example, healthcare workers, law enforcement, food delivery and supply workers, the elderly, nursing home residents etc.
Indeed, this is being proposed in many parts of the world already;
however, we believe that sound studies are needed before such blanket recommendations can be made.
Virus-specific memory T cells are crucial in broad and long-term protection against SARS-CoV infection 34 and this has been clearly documented in several animal models. 35 Structural antigens of SARS-CoV act as a major antigen for both humoral and cellular immunity. 36 These studies, thus, suggest a potential mechanistic rationale for protective effect of BCG against the cytokine storm induced by COVID-19 infections, which will be studied in the ongoing trials.
Bacillus Calmette-Guerin is currently administered by several routes including: intravesically, sub-dermally, directly injected into certain tumors, intra-nasally, pharyngeally or as an inhalation spray directly into the lungs. There presents an opportunity to re-purpose intravesical BCG for use as a potential protective agent against SARS-Cov-2. In addition to consideration for intradermal injection, inhalation or nebulization may be considered as, similarly to the bladder, this may allow BCG to act directly the upper and lower respiratory system affected by SARS-Cov-2. A potential inhalational form of BCG has already been developed and BCG may induce pulmonary mucosal immune responses at the point of entry of the pathogen. 44 The safety of the aerosolized BCG vaccine is well established without reported side effects. 45 
Many opportunities exist for the urologist and urology infrastructure to contribute to translational and basic scientific correlates to further the understanding of BCG vaccination in preventing COVID- 19 . Several animal models focusing on SARS-CoV-1 have previously been described. Viral replication has been reported in mice, hamsters, cats, civets, and primates, however, recreation of human disease in these models without viral passage to produce animaladapted variants has proven difficult. 46 For SARS-CoV-2, research efforts have identified that viral replication occurs in the respiratory tract of ferrets and cats when directly inoculated with virus. 47 Infection and rapid transmission of SARS-CoV-2 has been demonstrated in ferrets. 48 Utilizing BCG vaccination in emerging animal models may help to better understand the rate of generation of immunity, the mechanism of possible immunity and/or disease severity reduction, and the optimal dose of BCG to administer 49 on a timescale allowing for more rapid understanding and deployment with the caveat that animals models do not fully recapitulate human disease pathogenesis. 50 For translational efforts, the urologist and urology facilities may play a pivotal role in BCG reconstitution and administration including opportunities to play a pivotal role on, or in leading the research team.
The administration of the BCG vaccine, both for bladder cancer and for the prevention of TB, is safe and has been utilized in over four billion people. There is an association between BCG vaccination and decreased childhood lung-related mortality as well as improved vaccination efficacy for yellow fever and some influenza strains. While the exact mechanism of action is non-specific, im- 
This research project was supported by the Wayne B. Duddlesten
Professorship and the Maria Floyd Research Award to Dr. Kamat. 