Tackling two pandemics: a plea on World Tuberculosis Day.

We are facing an unprecedented pandemic. A quarter of the world's population is infected and, between 2020 and 2021, it is predicted that 10 million people will have fallen ill, 3 million will not have been diagnosed or received care, and more than 1 million—mainly the most vulnerable—will have died. This pandemic is not COVID-19 but tuberculosis. On World Tuberculosis Day, it is worth comparing the COVID-19 and tuberculosis pandemics to ensure that, while we focus on the former, we do not forget the latter.

A pandemic is defined as a disease that spreads across whole countries or the whole world. Tuberculosis and COVID-19 are both pandemics that show ongoing, sustained community transmission across continents. Indeed, no country is tuberculosis-free and this is likely to be the case soon for COVID-19.

There are striking similarities between the two pandemics. Both cause major infection-related morbidity and mortality around the world. Tuberculosis was the leading cause of mortality from an infectious disease worldwide in 2018, causing 1·2 million deaths. COVID-19 has infected more than 300 000 people and caused over 13 000 deaths in the first quarter of 2020 alone. Both COVID-19 and tuberculosis can present with respiratory symptoms, and diagnosis and treatment of people with tuberculosis, or tuberculosis and COVID-19 co-infection, are likely to be compromised during the COVID-19 pandemic. Older people and those with comorbidities are at increased risk of severe disease and adverse outcomes in both diseases.3, 4 And, as we are discovering for COVID-19, both diseases have considerable social impact—including stigma, discrimination, and isolation—in addition to the economic impact from country productivity losses and catastrophic costs to individuals and households.

There are also stark differences. While tuberculosis is a slow pandemic and has accompanied humankind for millennia, the coronavirus (SARS-CoV-2) that causes COVID-19 is new and spreading rapidly around the world. Tuberculosis has been labelled a pandemic many times over the past three centuries, whereas this is the first COVID-19 pandemic. Children are less severely affected by COVID-19, whereas 1·1 million children had tuberculosis disease in 2018, of whom 200 000 died. The vast majority of cases and deaths from tuberculosis occur in low-income and middle-income countries, whereas high-income countries have low rates. By contrast, Europe became the second epicentre of COVID-19 after China, which might explain, in part, why COVID-19 can be expected to mobilise more global resources and person-power in a year than tuberculosis has in decades. However, underprepared and vulnerable countries in sub-Saharan Africa and Central and South America might soon see substantial rises in COVID-19 cases and deaths, and concerted, collective action must be taken now to avoid catastrophe.

There are many unknowns. The clinical and epidemiological interactions of COVID-19 with tuberculosis (with or without HIV) are likely to be highly complex. Simply put, tuberculosis transmission might rise because of increased respiratory symptoms associated with COVID-19, or decline owing to COVID-19-related self-isolation and quarantine. There is increasing recognition of the millions of people treated for tuberculosis who have residual, long-term lung damage who are likely to be at a higher risk of severe disease and death from COVID-19. Because of extreme pressures on health systems, exacerbated by COVID-19, people with tuberculosis are likely to face decreased access to diagnostic and treatment services, which might also result in adverse outcomes.

Tuberculosis disproportionately affects men and boys compared with women and girls. Early data show that more men are dying from COVID-19, potentially due to sex-based immunological differences or gender-based factors such as prevalence of smoking. The association between COVID-19 and poverty is also unclear but, as more data become available, we will be able to better understand the differential effects of COVID-19 according to socioeconomic position. COVID-19, like tuberculosis, will almost certainly be associated with the medical poverty trap, in which poorer people have a higher likelihood of infection, disease, and adverse outcomes. Moreover, unemployed populations and informal or so-called zero-hours contract workers will experience further impoverishment, which increases risk of tuberculosis.

Amid the expanding COVID-19 pandemic, our plea on World Tuberculosis Day is that we do not forget the tuberculosis pandemic, which, at present, is still the leading cause of infectious disease mortality. We need to continue to mobilise funding for research for better tuberculosis diagnostics, vaccine development, novel therapeutics, equitable access to care, and innovative social protection interventions for tuberculosis-affected households. We should drastically increase and sustain investment in health systems that are responsive to the needs of the poor and resilient to the threat of infections, especially those that are air-borne and require isolation facilities. We need to continue to inform, advocate for, and empower local communities and to lobby governments and policymakers to ensure that tuberculosis, as well as COVID-19, remain high on the global agenda. These two pandemics, one old and one new, remind us of the need to be proactive and long-sighted, to plan ahead, and to not become complacent.