SARS’ fingerprints on COVID-19 pandemic

My 7/18/2020 blog first wondered what explains the differences in SARS and COVID-19 consequences, and how the global responses have been guided or affected by the previous SARS experience.  The second question, in particular, had not been asked before.

For background, both SARS and COVID-19 are caused by CoVs, 80% identical, with similar transmission mechanisms and symptoms.  SARS has a higher fatality rate (10%) than COVID-19 (<1%).  SARS is a faster onset and more severe disease, while COVID-19 is more sneaky, producing many pre-symptomatic patients who are infectious.  Between SARS and COVID-19 there was MERS, which impacted primarily the Middle East and South Korea, and was by all accounts like SARS.  Before SARS there were also several CoVs known to cause mild cold/flu like symptoms.   

The contrast in SARS and COVID-19 outcomes couldn’t have been starker.  SARS led to “merely” 8K infections and 800 deaths around the world, with the most cases and 400 deaths in China.  Guangdong had the first known SARS case in Nov 2002.  For months it went under the radar, with a cause unknown until well into 2003.  Only when SARS caused local transmission in Beijing hospitals in Feb and March 2003 did the Chinese government acted.  Even then, neither Guangdong nor Beijing was locked down, and most people didn’t wear a mask.  Once SARS was over in June 2003, it was considered too deadly, even though cold/flu kills far more people each year.  Well, nobody has seen nothing yet.

Here lie the questions: Why was SARS a smaller outbreak than COVID-19?  Why didn’t SARS infect more people when nobody paid attention for months, when SARS and COVID-19 are on the surface similarly contagious?  Can the differences in symptom onsets and severity, which likely means that COVID-19 carriers were harder to identify, adequately explain why the COVID-19 pandemic was so much worse?  At this moment there are no studies analyzing and quantifying these questions.  May also involve some pure chance or good/bad luck as well.  But I propose that our prior experience with SARS (and other CoVs) influenced our responses in 2020, likely can explain some of the early judgements and actions, and led in part to the current situation.

When the Wuhan doctor Zhang Jixian realized that the 7 patients she saw might have a new disease on Dec 26, 2019, she alerted the authority because of a connection to the Wuhan Huanan Seafood Market, as a disease jumping from animals to humans, like SARS, was suspected.  Still, how do you ascertain it is a new disease, especially when the symptoms are cold/flu like, in the midst of a high cold/flu season?  There are dozens of known pathogens that cause cold/flu, so one has to rule them out one by one, verify in multiple patients, not an easy task.  But by Jan 3, 2020 all the usual suspects were out, and it was indeed a new disease, so WHO officially notified.  Sequencing was performed, coupled with a novel CoV isolation on Jan 7.  On Jan 11 the new CoV and genome was announced (the first sequence was uploaded on Jan 5).  Compared with SARS, which took months.  So far so good.

Now the prior experience with SARS set in further.  It is a CoV, so likely human-to-human transmission, but of the close contacts of the first generation patients, few had showed any symptoms.  If it was like SARS, why hadn’t we seen more sickness earlier?  But if not, why were the enrolled patients as sick as SARS?  These questions must have vexed the doctors in Wuhan and the first two teams of experts sent by Beijing.  

This was the backdrop of the fateful statements by the experts on Jan 14 that human-to-human transmission can’t be ruled out or may be limited.  In hindsight, mid Jan was the time when the 2^nd generation of COVID-19 transmission would start to get sick.  Moreover, being sick still doesn’t mean human-to-human transmission, as one could get the virus from the animals or meat brought home, another SARS lesson.  Test kits were being developed around this time, which would identify more patients, not just among the close contacts, and the most importantly, tell COVID-19 from other diseases.  Recognizing more patients finally allowed the 3^rd team of experts to conclude human-to-human transmission on Jan 19.

By this early junction, one can see the SARS experience already made huge impacts.  The first is that by raising the awareness of a possible zoonotic jump it helped to identify a new disease, a positive.  The second is that by looking for quick and acute symptoms like in SARS, the possibility of presymptomatic and asymptomatic COVID-19 was not considered, a negative.  The third is that trying to rule in or out a zoonotic jump led to a dead end, and like the second point above, delayed the human-to-human transmission assessment, another negative.  Of course, presymptomatic and asymptomatic would be known soon afterwards, and without testing one can’t diagnose more infections, so it always takes time to gather evidence.  Crucially, the two negatives were well within the normal learning curve, while nothing followed without the first positive. 

Unlike SARS, when the Chinese government knew or did little for months, on Jan 23, 2020 Beijing ordered a Wuhan lockdown, determined to avoid the repeat of 2003.  Other measures soon enacted, and everybody wore a mask.  But because of the spread, fueled by the presymptomatic and asymptomatic, COVID-19 likely already infected thousands, including medical staff, in Wuhan by Jan 23.  

The goal now turned to treat the patients and stop the transmission, as in any infectious disease.   Hence the Chinese COVID-19 response was similar to the SARS response, only with effort 10x or more.  With the situation more serious than in 2003, medical staff around the country soon poured into Wuhan and Hubei, and two hospitals were built in about 10 days in Wuhan, with more buildings converted to shelter hospitals to treat and monitor the mild cases.  One thing different from SARS, though, is that the Chinese doctors and scientists this time contributed the most to the understanding of COVID-19.  Obviously the identification and sequencing of the virus within 2 weeks.  Then elucidating the transmission routes, symptoms, presymptomatic and asymptomatic carriers, who are susceptible and who are not, fatality, etc, by the end of Jan, and various treatment options during Feb.   

   

By early Feb COVID-19 in China was already worse than SARS globally.  By Feb 20, when COVID-19 was dying down, it was clearly the worst China has seen in living memories, but most people in the world would think we’d just survived a badder SARS, and that was it.  Yet how other countries had applied their SARS experience would show the results soon.

For every country, the only historic reference for COVID-19 was SARS (MERS lesser).  The following reasoning by the West and US was hard to fault.  China didn’t do much for a few months with SARS, and ended up with most of the SARS cases and half of the deaths in the world.  Chinese reported COVID-19 death rate lower than SARS.  China actually acted much faster in 2020.  So if the SARS precedent holds, other countries will do no worse than China.  And by banning Chinese entry, we would do even better than in 2003.

Many statements and (in)actions by the West from Jan to March can now be finally explained or understood in light of this logic.  Remember a lot of people were saying it was just a flu?  Getting it was no big deal?  Because it was a flu or SARS, masks were not needed, per Western traditions.  Since it would end up better than SARS, little preparation was needed.  And why miss a chance to bash China when you can?

Now the outcomes have been so dramatically different, what went bust?  The Chinese data are not wrong.  Their fatality rate is in line with rest of the world.  The critical scientific findings out of China have been confirmed time and time again by later studies from other countries.  Perhaps what the West missed was that, despite China’s drastic measures, COVID-19 still ended up inflicting a much heavier toll than SARS, indicating that COVID-19 is on a different level from SARS.  Cases are easy to miss, and superspreading can get out of control quickly.  These should have raised a big red flag early on for everybody, never a license for complacency.  Should have paid attention to what China did: lockdowns, masks, etc, rather than taking it as a fact-free article of faith that China always screws up (7/18/2020 blog).  If China did, did the West, with a 1-2 months’ head start, not? 

There are also countries that do well.  East and SE Asians started to wear masks quickly.  South Korea, experiencing MERS a few years back, planned for COVID-19.  Germany also had an early surveillance and testing program.  They were still hit harder than by SARS for a couple of reasons.  First is COVID-19 is just difficult to tame.  Second is bad luck, and once the virus has gone global and long-lasting, repeated importation and superspreading become unavoidable.  A superspreading event led to cascades of almost 10K cases in South Korea.  Japan was the most affected by cases from the US.  Germany was heavily impacted by its neighbors that didn’t prepare as well as Germany.     

     

Past experience plays an integral part in learning.  Undoubtedly the SARS saga in 2003 has greatly influenced the global COVID-19 responses, both positively and negatively.  Looking back 17 years ago is important, so is looking at two months ago, one month ago, or in real time.  At the end of the day, (mis)applying the SARS experience is only one of the many intertwined reasons that have got us here (7/18/2020 blog).