Pneumonia outbreakwith novel coronavirus in China COVID-19 – update

Seven weeks have passed since the World Health Organization (WHO) on 5 January 2020 for the first time announced an outbreak of pneumonia of unknown cause in Wuhan in the Hubei Province of Eastern China.

The outbreak was linked to a fish market where other non-domesticated animals were also sold. Already on 7 January, it was announced that the cause of the outbreak was a novel type of coronavirus similar to the coronaviruses found in bats, but also similar to SARS coronavirus.

It was established that the new virus could be transmitted effectively between humans. Now - approx. one and a half month after the outbreak was acknowledged - a total of 75,000 cases and 2,000 deaths have been detected worldwide. Even so, 98.8% of all cases have so far been detected in China (74,279/75,197), and only six deaths have been recorded outside of China.

Changed registration in China triggered considerable increase

On 13 February, China changed the manner in which cases are recorded in the Hubei Province to also include suspected cases with image-diagnostic signs of pneumonia.

This caused the number of recorded cases to increase by 13,332 clinical cases and a total of 245 deaths in a single day. Nevertheless, these clinical cases and deaths were, in fact, distributed on a longer period, and were therefore not a sign that the epidemic was expanding rapidly.

New study from China indicates that the outbreak has peaked

Rather, the daily number of new recorded cases in China follows a slightly decreasing trend and has done so since 6 February. Furthermore, there are no signs of substantial spread of the infection in other countries than China.

On 17 February, the Chinese Center for Disease Control and Prevention (CCDC) published its first detailed epidemiological analysis of the Chinese outbreak. The report is based on 72,314 cases recorded in the national monitoring system from the outbreak started on 8 December 2019 to 11 February 2020.

The majority (78%) of the recorded cases have occurred in the 30-69-year age group. More than four out of five (81%) of these cases have experienced a mild disease course, whereas less than 5% have been critically ill. Most patients (86%) are considered to have become infected in Wuhan or by persons associated with the province.

Finally, the report shows that with respect to onset of symptoms among confirmed cases, the epidemic peaked in China in the period from 23 to 27 January.

“Much therefore indicates that the outbreak of novel coronavirus in China is receding and that the outbreak did, in fact, peak in late January. This is extremely encouraging news as it shows that all of the measures implemented in China probably have an impact,” notes Division Head Kåre Mølbak, Statens Serum Institut (SSI).

If a vaccine is achieved, it will not be available for another year

Currently, no approved vaccines are available against SARS-CoV-2, the name coined for the novel coronavirus.

Work is underway to develop several types of experimental vaccines, including so-called DNA, RNA and subunit vaccines, which will possibly start being used in trials in the course of some months. Initially, though, the vaccines need to be tested on animals and then on a small group of humans to explore their effect and establish any side effects.

“Another year will probably pass before the vaccines are tested in larger groups of people,” notes Kåre Mølbak.

What we do not know yet

Many aspects of the new virus currently remain unknown.

Among others, it is still unknown from which animal SARS-CoV-2 originated.

It also remains unknown if an intermediary host was in play. An intermediary host is another species of animal that has become infected before the virus adapted to become capable of being transmitted to humans. Additionally, it has become clear that cases of COVID-19 that were not linked to the fish market were also detected in Wuhan in December 2019. This may mean that the virus had already been transmitted to humans in this period. It may also mean that the spread via the fish market was not due to animal-to-human transmission but rather human-to-human transmission.

Despite the recent Chinese study, it therefore remains unclear exactly how many unrecognised mild cases of COVID-19 have occurred in China. Both within and outside of China, a range of asymptomatic and mild cases has been detected. It is therefore probable that the real number of infected people in China is far higher than suggested by the official figures. This is underpinned by mathematical modelling studies, which have estimated the number of disease cases to be 10-20-fold higher than the official estimates.

“If the real number of infected people is considerably higher than the reported number of cases, overall mortality will be lower than the currently recorded approx. 2.3% mortality. On the other hand, there are also indications that the serious COVID-19 cases may remain ill for many weeks before they succumb to the infection. This may mean that the mortality would instead increase,” notes Kåre Mølbak.

Finally, the infectious period of COVID-19 also has to be fully elucidated. Virus has been found in the upper airways in people presenting with mild symptoms. Similarly, examples have been observed of infection prior to symptom onset. But the possible effect of transmission from asymptomatic or mild cases on the spread of the infection remains unknown.

Read more

Read more about the current state of the coronavirus outbreak in EPI-NEWS.

Read more about the coronavirus outbreak on the SSI’s outbreak page.