What we know about asymptomatic cases of Covid-19 

  1. What is an asymptomatic carrier?

An asymptomatic carrier is a person who is infected with SARS-CoV-2 (tests positive for it), which is the virus that causes Covid-19, but displays no clinical symptoms. There are two possibilities: 1. Some people never develop any symptoms throughout the course of the infection, and the body just clears the virus on its own. 2. Some people develop symptoms later  —  the pre-symptomatic phase is called the incubation period, which is usually between 2 and 14 days.

Here we are talking about the first category: those who never develop symptoms.

  1. Can asymptomatic carriers of SARS-CoV-2 pass it on to other people?


  1. How many asymptomatic cases out there?

We don’t know. But here is a summary of some of the existing evidence.

(Note that when the screening is aggressive, the number of true asymptomatic carriers can be overestimated, because some people might test positive when they are in the incubation period. The share of asymptomatic cases on Diamond Prince was around 50% at some point, but some developed symptoms later.)

Taken together, most existing evidence seems to suggest between 20–30%.

  1. How are asymptomatic cases discovered? 

In South Korea and Iceland, mass testing.

In China, the NHC says there are four main ways: 1. monitoring of close contacts; 2. investigation of clusters; 3. investigation of source of infection; 4. screening of population groups who have been to high-risk areas.

More recently, a few publicly reported cases were discovered through “get back to work” screenings (employers ask employees to test for coronavirus or offer free tests before they can get back to work). In Henan Province, three doctors tested positive without displaying symptoms in the screening organized by the hospital they work at in order to resume normal healthcare services. A resident in Wuhan tested positive without symptoms on 17 March after his employer required all employees who had infected family members to provide testing proofs. This resident’s father was diagnosed in January. He was not tested back then because of shortage of testing kits in January.

  1. What is China’s policy on reporting asymptomatic cases?

The NHC confirmed that asymptomatic carriers can be infectious in its “Covid-19 Diagnosis and Treatment Plan” (5th Edition), published on 4 February.

On 5 February, the NHC instructed that asymptomatic cases should be included in confirmed cases.

However, since 7 February, with the publication of the “Covid-19 Prevention and Control Plan” (4th Edition), asymptomatic cases have been excluded from the count of confirmed cases. They become counted as “confirmed cases” if symptoms are developed. The numbers are still reported to healthy authorities, but not disclosed to the public.

Since 31 March, the NHC has been disclosing the daily active number, but not the cumulative number.

  1. What is China’s policy on the management of asymptomatic cases?

According to the “Prevention and Control Plan”, once detected, asymptomatic cases should be reported to the CDC system within 2 hours. Local health authorities should complete the epidemiological investigation for each individual case within 24 hours. Asymptomatic carriers should be put in centralized quarantine and monitored for 14 days. In principle, the quarantine can end after 14 days and if the person tests negative twice. But the quarantine period should be extended if they still test positive. The close contacts of asymptomatic carriers should also be quarantined for 14 days.

The Wuhan resident mentioned earlier shared his own experience as an asymptomatic carrier. He was sent to Jinyintan Hospital – the specialist infectious diseases hospital that has treated the most severe cases during the outbreak – and hospitalized for some 7-8 days even without displaying any clinical symptoms. He was given antiviral medication. After discharged from hospital, he was quarantined in a hotel. His mother was also quarantined in a hotel for 14 days and tested several times (negative).

7. Lessons?

Wear a mask.

never forget.

All makeshift hospitals in Wuhan have closed as of today (10 March 2020).

The darkest hour is finally gone.

But it’s not time to celebrate, but to remember. Remember the lives lost and millions of hearts broken.

Remember the daughter and the wife chasing the hearses carrying their loved ones.

Remember the woman playing the gong on the balcony crying for help because her mom was dying and nowhere to be treated.

Remember the disabled boy who starved to death at home because his father was taken to quarantine.

Remember the person who killed himself because no hospital bed for him and he dared not return home for fear of passing it on to his family.

Remember the migrant workers who helped build this city and have been forced to sleep rough since the lockdown.

The migrant care workers who had no home to return after they got infected while caring for patients, and no shequ (community) to apply for hospitalization for them because they don’t have Wuhan hukou.

And the migrant workers who helped build a hospital miraculously in 10 days only to face discriminations and dreadful quarantine conditions when returned home.

Remember the woman medical workers who shaved their head and then their body was used by state media as a propaganda tool.

Remember the person who donated all the masks that were substitute for his unpaid salary.

Remember the director whose entire family of 4 were killed by the virus.

Remember the family of 5 – a young couple and their 3 children – who travelled from Hubei to Quanzhou and were all killed by the collapsing of the quarantine hotel they were placed in.

Remember the pregnant woman from rural Hubei who gave up treatment after her family had borrowed and spent 200k CNY on health care and they couldn’t afford it anymore. The doctor said her conditions were improving. The next day after she died, authorities announced free treatment for all covid-19 patients.

Remember the grandpa who learned to use weibo to seek for help after his daughter had already died from covid-19 and both granddaughter and himself were infected. He died a month after he sent that first “nihao” post.

Remember the 29-year-old doctor who died of covid-19, leaving behind her 2-year-old son and her husband and first love. They had met in medical school and planned to “grow old together”.

Remember the doctor who wrote “I can” & “I understand” on that “letter of reprimend”.

We’ll never know the full extent of it. But for the tip of iceberg we know: Never forget. Never forgive.


Crowd-sourced online archives:



Politics and the Chinese language

I doubt if I’ll have time for any ‘serious’ blogging here but for now I might use this place for organizing and recollecting some of my tweets – or, fragments of thought in the time of fragmentation. Today’s theme is politics and the Chinese language, including political “newspeak”, internet slang terms, and some other stuff.

If interested I also wrote something about how censorship has corrupted the Chinese language on my 中文博客.

Beijing, 2014