Infectious Diseases Have Rules: Lessons from the Past for Facing COVID-19

 

COVID-19

 

By Drs. Myron Cohen and Wafaa El-Sadr

As the global community finds itself increasingly overwhelmed with COVID-19 developments, it’s a good time to go back to basics and review public health strategies that have proven successful for generations. Humans have since time immemorial been confronted by new microbes – “emerging pathogens.” Whenever this happens, it brings great alarm. But we have been here before with HIV, Zika, SARS and many other microbes, each of which lives (and dies) by its own rules. The same steps that led to discovering how to prevent the transmission of earlier emerging pathogens are being put to work to fight COVID-19.

As with any disease, the goals for COVID-19 are prevention and treatment. The first priority in prevention is to understand what governs the behavior of the organism and its intersection with us, the human host. To prevent COVID-19, we must understand how SARS-CoV-2, the virus that causes the disease, is transmitted, who gets infected, under what conditions, and how much virus is needed to cause infection. These parameters define how infectious someone with COVID-19 is and should clarify the risk of acquiring the infection from person to person or environmental (surface) exposure. Is everyone equally susceptible to the SARS- CoV-2 virus? Are some people immune, and if so, why? We have yet to answer these questions reliably, but effective and efficient prevention strategies depend on getting these answers.

Fortunately, for most people, COVID-19 is a mild illness. But for a minority of people, the infection progresses to severe symptoms and even to death. Some of the risk factors for progression of disease have been described: men have fared worse than women, as have people with high blood pressure, diabetes, and heart and lung diseases. But we don’t know why. Understanding the progression of the disease defines what we call the rules of the “pathogenesis” of the organism. Progression of disease depends on a delicate balance between the virus and our immune defenses. Understanding what shifts this balance is critical to developing strategies to reduce morbidity and mortality.  

Before we learn the answers to transmission and pathogenesis questions, we have to proceed with prevention and treatment. With every new infection, attention immediately shifts to the need for a vaccine. 

Preventive vaccines are perhaps the greatest advance in the history of our species. They have been used to control smallpox, polio, measles, and many other diseases. But vaccines take time to design and test, and they don’t always work or work as well as we would like. Vaccine development for preventing COVID-19 is already progressing. Such development requires an evaluation of safety for healthy volunteers and then testing the vaccine compared to a placebo in a highly exposed population.  

Given the challenges of vaccine development, we need an alternative means of prevention. The first line of defense is changing human and population behaviors. If we understand and communicate the rule of transmission of a microbe, humans have proven very adaptable. For HIV infection, we saw massive changes in sexual behavior once people realized how HIV was being transmitted. For COVID-19, we have deployed increased hygiene, social distancing, mass testing, and isolation of people with the disease. While these may seem like crude tools, they proved remarkably effective in China, Singapore, and Korea, as well as in previous epidemics of influenza. Conversely, the rapid spread of COVID-19 in Europe and the US reflects how difficult it can be to deploy these strategies rapidly and universally.

And finally, we must develop an effective treatment for COVID-19, emergently. Currently, the most effective way to handle COVID-19 is supportive care in the absence of proven anti-viral drugs. Oxygen and ventilators to deliver oxygen to the most severely ill people with COVID 19 pneumonia are lifesaving. Pharmaceutical drugs that can stop the replication of the virus and prevent the disease from progressing are desperately needed. If treatment can stop viral replication, it should decrease a person’s infectiousness, i.e., prevent them from transmitting to others. This is what has been coined as “treatment as prevention.” Treatment of people living with HIV virtually eliminates the transmission of the virus, and “treatment as prevention” is currently the lynchpin of HIV prevention.

Effective treatments for COVID-19 likely will be identified much more rapidly than vaccines. The large number of persons with COVID-19 and the fact that it is an acute infection should allow us to quickly test promising drugs and measure their effects. 

However, treatment studies must be rigorously designed and implemented to provide convincing scientific evidence of a drug’s safety and effectiveness. Anecdotal experiences are provocative and hopeful but can be very misleading. Once effective drugs are identified, making them available to all individuals with COVID-19 will be vital, benefitting not just those who are sick and perhaps concomitantly decreasing transmission of the virus to others.  

SARS-CoV-2, an emerging pathogen, has reshaped the world in just three months. But as devastating as this virus has proven, it must live (and die) by the traditional rules that govern all infectious diseases. We need to deploy strategies for prevention and treatment that we know will work. We have no time to waste.   

 

Dr. Myron Cohen is HPTN co-principal investigator, and Yeargan Bates Professor of Medicine, Microbiology, and Immunology at the University of North Carolina at Chapel Hill, where he directs the Institute for Global Health and Infectious Diseases. 

Dr. Wafaa El-Sadr is HPTN co-principal investigator, and founder and director of ICAP at Columbia University and a professor of epidemiology and medicine at Columbia’s Mailman School of Public Health.