The anatomy of a pandemic: Silent infections could erode containment efforts’ efficacy

By: |
March 13, 2020 2:00 AM

Silent infections could erode containment efforts’ efficacy; developing anti-virals and vaccine must be part of the near-term vision.

covid 19, coronavirusCOVID-19 is likely to have multiple viral shedding routes.

It has been little more than three months since the novel coronavirus, now called SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), and the disease it causes (COVID-19), first emerged in Wuhan, Hubei, China, in December 2019. On January 30, 2020, the World Health Organization (WHO) declared the outbreak a “public health emergency of international concern”, and on March 11, 2020, it declared it a pandemic. As of March 11, over 126,000 cases have been confirmed in more than 110 countries. More than 4,600 people have died from the disease, and 67,000 have recovered.

Data from China and Italy, the top two countries in terms of confirmed cases and deaths, indicate that COVID-19, in initial stages, increases exponentially. Italy, for instance, had 62 identified cases on February 22. This increased to 888 cases by February 29, 4,636 by March 6, and 12,462 cases by March 11. So, in the first week it increased by a factor of 14, in the second week, by five and in the third week, by a factor of three. The question is, why is there such rapid increase despite massive containment efforts? To answer this, we have to analyse data, and studies (most of them being preliminary) to discern the characteristics of this outbreak.

The first trend that emerges is that mild and asymptomatic cases characterise COVID-19. More than 80% of the patients worldwide with confirmed COVID-19 have a mild symptom. Though an estimate of asymptomatic cases is complicated to ascertain, the results from the Diamond Princess cruise ship—the coronavirus-stricken ship disembarked in Japan—indicate that more than 10% of confirmed cases were asymptomatic (an infected person producing or showing no symptoms). A large proportion of mild and asymptomatic cases suggests that we might have many more infected people than is being reported. Prevalence of asymptomatic cases also means that the temperature screening at the exit and entry points on borders (like on airports) is likely to miss some infected people.

Studies indicate that COVID-19 infectious period (a period during which an infected person infects others) starts quite early in the disease cycle. In many viral diseases, the peak viral shedding (when an infected person releases the maximum amount of virus from the body into the environment) occurs after patients are already quite ill. So, it is easy to identify and isolate them. Preliminary data shows that in COVID-19, viral shedding starts in the early phase of the disease, when the patient has not got a full-blown illness. This means that the isolation of only severely ill patients is too late. Infected patients should be quarantined from the very beginning.

COVID-19 also seems to have high transmissibility. R0 is a unit to measure how contagious an infectious disease is. R0 measures the average number of people who will catch a disease from one infected person. If R0 is less than 1, the disease will decline, and eventually die out. If it is equal to 1, the disease will stay alive and stable, but there won’t be an outbreak, or an epidemic. If R0 is more than 1, then the infection will spread between people, and there may be an outbreak or epidemic. A preliminary review found the average R0 of COVID-19 to be 3.28. This is higher than that of the 2003 SARS, or the 2009 swine flu epidemic. It is important to remember that this is a preliminary estimate, and this number might reduce by the time the pandemic is over. High transmissibility indicates that the person-to-person infection, or community spread, is a prominent feature of COVID-19. The Chinese experience also substantiates this.

China has been able to contain the spread by enforcing the most extensive community quarantine in history. It has forced people to stay at home, and imposed movement restrictions through an exit-entrance permit. To feed people, it has organised logistics on a vast scale to deliver food to homes. With these draconian measures, it has been able to exercise some control on the number of “reported” infected people. But, some models indicate that China might already have several hundred thousand ‘silent’ infections.

Lastly, COVID-19 is likely to have multiple viral shedding routes. Apart from the airborne transmission, initial studies indicate that the infected person is also likely to shed the virus through faeces. This has huge implications for a country like India, where faecal-oral transmission is a prominent source of diseases like diarrhoea, typhoid, cholera, and hepatitis.

The ramifications of the above characteristics are enormous. The first is that we might be missing asymptomatic patients, and those with very mild symptoms. These infected people might spread the disease silently, similar to the swine flu pandemic of 2009.

The second is that this virus will remain in the human environment, and would continue to infect people, like swine flu. Though swine flu is no more a pandemic, it is now more or less an annual feature in a country like India. We have had more than 25,000 cases of swine flu in 2019.

The third ramification is that the preventive measures we have instituted, like isolation, social distancing, travel control, and improved hygiene, will reduce the speed of the spread of infections, but might not reduce the total number of infected persons. Still, the slower pace of the outbreak will save the lives of most of the infected people because the healthcare system will be able to cater to the patients. If there is a rapid outbreak, the healthcare system will be overwhelmed, and this would lead to more fatalities.

Lastly, as we might not be able to halt human-to-human transmission, we need to very quickly develop anti-viral drugs, and a vaccine to cure this disease. This can only happen through a global collaborative effort. Countries must quickly come together and pool resources in this endeavour. We do not have 1.5-2 years for vaccine development.

SARS: How a global epidemic was stopped is a book published in 2006 by the WHO Regional Office for the Western Pacific Region (WPRO). In the final chapter, Brian Doberstyn, who was the Director, Division for Combating Communicable Disease, WPRO in 2003, has penned some crucial lessons learned during SARS. One of the lessons he mentions is that “twenty-first century science played a relatively small role in controlling SARS; nineteenth-century techniques proved their value”. The nineteenth-century techniques he is referring to are preventive measures like quarantine, travel ban, and social distancing. Many people are referring to the experience of SARS to tackle COVID-19 as both are caused by coronavirus. I believe comparing SARS and COVID-19 is wrong. COVID-19 is displaying tendencies more similar to the swine flu than to SARS. We, therefore, will need both the nineteenth-century techniques (prevention), and twenty-first century science (drugs and vaccines) to control a disease like COVID-19. Relying on one would be foolhardy.

The writer is CEO, iFOREST. Twitter: @Bh_Chandra. Views are personal.

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