Following a long period of Zero COVID tolerance, China and Hong Kong are witnessing faster and widely spreading waves compared to earlier waves. Despite the current lower death rate, these countries may face a transient shortage of medical resources in the short term.
Any wave in any part of the world occurs when the susceptible pool of uninfected people crosses a population-level threshold. This is a defining feature of any infectious disease outbreak. Almost every wave may be characterised as a state of disequilibrium caused by the interaction of three elements of the epidemiological triad. Understanding the virus (agent), the human (immune) response (host), and environmental factors is required to comprehend how susceptible pools are formed. The agent (SARS-CoV-2) is distinguished by the emergence of newer variants, whereas at the host level, the duration of protection provided by antibodies dwindles over time. Compliance with mask and crowding restrictions, as well as proactive actions implemented during waves are examples of environmental influences.
In China and Hong Kong, imposing severe restrictions such as lockdown changed only the environmental factors, transiently protecting the susceptible pool and eventually postponing the waves. Air cannot be shut down; the virus has an unrestricted global pass disregarding geographical boundaries. With Omicron and its stealth form, any person with an infectious variant, once connected to a susceptible pool can cause massive outbreaks. South Korea, which was initially lauded for its better control, is reeling under pressure, with hospital bed occupancy reaching 64%, despite 63% of the country’s 52 million population receiving booster shots. China, on the other hand, has achieved 38% booster dosage coverage and is at the tipping point, to witness significant number of infections, when it has to open up eventually.
Several factors influence the natural course of the COVID-19 pandemic. Among them, the action taken in the first and subsequent waves play a significant role. Velásquez et al from the Universidad Nacional de San Agustín de Arequipa, Perú, use the example of three countries that experienced identical illness transmission dynamics during the first month, then differed due to government policies such as quarantine, closed borders, and other restrictions. As a result, rather than local strategies, a viable exit strategy for COVID-19 should take the form of a global control program. A few countries that tried Zero COVID policies locally (New Zealand, Australia, and now China) were unsuccessful and will be compelled to abandon this plan.
Lessons for India
The goalposts for attaining herd immunity have shifted with COVID-19. The fallacy of herd immunity is perpetuated by an incorrect characterisation of a similar strategy against stable viruses, as well as the belief in long-lasting immunity, both of which have been disproven. A ‘wave’ arises when there is a substantial enough number of cases in a specific period.
The lesson from ongoing waves is that the Omicron variant is unstoppable, both in its original and modified forms, and is destined to spread to nearly every part of the planet. China’s Zero COVID approach and South Korea’s early success can no longer deter its spread. Is that a good sign? Uncertainty is the only certainty at this point, depending on what happens next in the virus’s evolution. It would be a relief if this is the last of the virus’s iteration, attuned to cohabit with humans. Alternative trajectories in viral evolution are equally likely, if not more probable, to result in either a more contagious or virulent newer version.
The problem in identifying future waves or other infectious disease outbreaks is that some areas do not have robust surveillance systems. Without knowing the expected number of cases of an illness, predicting the extra cases, which constitute a wave, is difficult. Areas with missed circulation provide a fertile ecosystem for the development of newer variants. More than ever, creating and strengthening surveillance systems to identify and tackle future disease outbreaks are essential lifesaving investments. Creating such systems must include enhanced spending by States in hiring and sustaining trained manpower, who can manage decentralised epidemiological and genomic surveillance programmes, using standard definitions and processes.
Monitoring the virus
Data from such this system can provide an expected and excess number of cases, to warrant initiating appropriate actions. Monitoring the virus and host-related factors over time necessitate the need of enhanced use of epidemiological tools enabled by strengthened and sustained efforts in syndromic and genomic surveillance, conducting regular serosurveys or establishing sentinel-based serosurveillance platforms. Given the uncertainty around how the virus will adopt, what is in our control is to track each of the constitution of epidemiological triad, and act proactively and early enough. We cannot afford to blame the new variant next time, not if, but when there is one.
(Giridhara R. Babu is a Professor and Head, Life course epidemiology at the Indian Institute of Public Health (PHFI), Bengaluru.)
