COVID-19 and the great Chinese puzzle

China does not know, or is not revealing, the magnitude of infection in the country

The pandemic is spreading like wildfire. What started surreptitiously in late 2019 in Wuhan, China, has engulfed 172 countries and regions by March 25, 2020. Globally over 4,35,000 have been reported as infected, over 19,500 have died, and around 1,11,000 have recovered.

To be clear, the virus is SARS-CoV-2; the clinical illness is COVID-19. When not specified, reported numbers may pertain to either infection or disease or a mix, misleading decision-makers to conflate the two.

The numbers of test results put out from China have helped the world get a sense of the seriousness of COVID-19 and SARS-CoV-2 infection. In China, about 81,600 had confirmed disease; there were about 3,100 deaths. The crude estimate of case fatality was 3.7%. All diseased are infected, the reverse is not true. Not all infected are sick or tested. Hence, information from China is unhelpful to confidently project the probabilities/proportions that will get infected; get COVID-19 symptoms; develop pneumonia; die.

Virus spread in China has reportedly stopped. China is now gearing up to prevent virus transmission from citizens returning from other countries. If only 90,000 were infected among a 1.4 billion population, the proportion was only 0.0065%. Here is the puzzle: for any epidemic, its downturn consequent to high herd immunity requires about 70% infected and immune. Every second person in the community will then be a dead-end for virus spread. What proportion of the Chinese was actually infected? The proportion of 0.0065% is unrealistically low for the visible shift in epidemiology. If 70% were infected, there were 980 million infections. This extraordinary range is the puzzle.

The beginning

The story began unfolding in December 2019 with cases of pneumonia without an identifiable cause. One physician saw this and alerted his colleagues. He was reprimanded by the authorities for spreading fear. Soon they realised that the alarm was true. Among the first 41 cases, most were workers in, or had direct contact with, the Hunan Seafood Wholesale Market. On December 31, health officials informed the World Health Organization (WHO) of the outbreak of a suspected zoonosis (vertebrate-to-human transmitted infectious disease). That market and all other similar markets nationally were closed the next day. On January 7, WHO was notified that the pathogen was a novel coronavirus. Soon Chinese scientists mapped its full genome sequence and gene sequence for primers needed for diagnostic tests and made these data publicly available. The International Committee on Taxonomy of Viruses re-named it SARS-CoV-2 because of its close genetic similarity to the SARS coronavirus. By mid-January, several countries reported COVID-19. It was no longer zoonosis but had become anthroponosis (person-to-person transmitted infectious disease). But when did this epidemic actually start in Wuhan? How long did it remain unrecognised? The number of cases at a given time could reflect the duration of the outbreak. The numbers are not available, which is a problem.

Only on January 11 did China record the first death from COVID-19. Considering that the test had just become available, any earlier death would not have been attributed to SARS-CoV-2 infection. More than a week later China counted 26 deaths among 830 diagnosed with COVID-19. By end-January, it alerted the world that COVID-19 was widely prevalent in all 31 provinces. By February 2, the infection had already spread to 24 countries outside China-Hong Kong-Macau. Given time this contagious anthroponosis was already a pandemic by definition. But WHO declared a pandemic only on March 11. Did WHO get misled by the 0.0065% risk? Countries like India that depend heavily on WHO guidance for public health action had apparently mistaken the non-declaration as a signal that it was short-lived/ non-serious. On March 12, fear gripped India as it had not done homework to face the pandemic and invoked the Epidemic Diseases Act giving the state extraordinary powers.

Growth pattern

Epidemiologists have estimated the transmissibility of SARS-CoV-2. The term basic reproduction number (R0) denotes the number of new infections that an infected person could seed, during the infective period, if all contacts exposed were non-immune and susceptible. For this infection, R0 has been estimated to be between 1.5 and 3.5. If we accept conservatively R0=2, one infected person will, on an average, infect two other people; next generation will be 4, then 8, 16, 32 and so on. When a large proportion is infected, hence immune, the scene changes. An infected person will encounter a majority of immune and a minority of non-immune among contacts, and virus transmission will slow down.

Experts outside China are projecting infection to reach 30-70% of the world’s population. Data from China indicate that 80% of the infected are likely to be not very ill. Around 14% would develop severe disease, and around 6% would require critical care. Consider these figures against a total of 90,000 reported infected in all of China and extrapolate to a probable 980 million infected. If countries use these estimates to plan resource demand, no country can claim to be prepared to meet these requirements. This is why the Chinese puzzle needs exploration. If only <1 % will be infected when the numbers begin to fall, countries like India have reason for optimism.

Or does this puzzle indicate that although 70% of Chinese were actually infected with SARS-COV-2 by the third week of March, only about 90,000 of the 980 million infected (0.0092%) developed COVID-19? This could also provide reason for optimism, but is highly speculative without necessary information. Why are the data missing? For infection rate to decline, the proportion of immune, hence non-susceptible people among the whole population should be fairly high. To determine how large the COVID-19 epidemic was in China is information that we need urgently. The only way to get it is by careful antibody prevalence surveys.

China claimed success in interrupting transmission because Hubei province was under lockdown fairly early in the course of the epidemic, and China also imposed travel restrictions on other provinces. Is its claim credible? What if the epidemic had actually started, say, in August?

Since the lockdown occurred later than it should have, travellers attending the Chinese Lunar New Year celebrations transmitted the infection wherever they went. Most countries have focussed on identifying infections brought by travellers from such high-risk countries but the majority with COVID-19 infections now are showing increasing rates of local transmission. The signal from the Chinese puzzle could be that widespread infection is not inevitable and with stringent public health measures infection rate could be brought down to zero. That scenario does not make epidemiological sense. We have to conclude that China does not know, or is not revealing, the magnitude of infection in all of China.

All countries that expected very small numbers to be at risk of infection based on the China puzzle must anticipate about 70% to be infected in the first wave of the epidemic. If summer heat dampens transmission, we may not reach 70% until autumn or winter. After that, the infection may stay on as endemic and seasonal. We have to catch up for lost time because of our optimistic reading of data that were not verified or even checked for plausibility.

T. Jacob John is retired Professor of Virology and Prathap Tharyan is Adjunct Professor, Christian Medical College, Vellore

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