COVID-19 in Sydney - timing, infectiousness and why New Year's Eve may be the mother of all super-spreading events

Sydney Fireworks - Wikimedia

A week before Christmas, Sydney is facing an outbreak of SARS-COV-2.  What makes it so hard to contain is that about half SARS-COV-2 infections are asymptomatic – infected people may not know they are infected and nor will others.  Further, 80% of transmission of the virus occurs indoors. Epidemics grow exponentially over a short period. Although the incubation period is 14 days, 90% of people incubate by 5-6 days, so that is the expected time between one generation of cases and the next. Unchecked, 40 new cases on Monday will be 120 new cases by Friday, Christmas day. Half of them will have no symptoms and the rest will be very early in the illness and have mild symptoms, so will carry on as normal.  The peak infectiousness of SARS-COV-2 is very early in the infection, usually before there are symptoms – making Christmas day a ticking time bomb. The people infected this week will travel halfway across Sydney for the family Christmas lunch on Friday and maybe to another household for dinner, infecting a minimum of 360 new people in their wake, maybe more, as the rate of social contact increases on Christmas day.  More Boxing Day parties will follow. Then, the 360 people infected on Christmas day will be at their peak infectiousness on New Year’s Eve.  Without any serious symptoms, they will party on at New Year’s eve events, not to mention all the parties between Christmas and New Year, and infect over a 1000 new cases. New Year’s Eve will seed a much bigger epidemic than Christmas day. You could not plan a disaster more perfectly if you tried.

 

The combination of silent infections, exponential growth and the calamitous timing of New Year’s Eve  being within 1 incubation period of Christmas day is a tinder-box, and the Sydney outbreak could not have come at a worse time.  Unlike most outbreaks in progress, we can pinpoint the exact date of expected super-spreading - December 25th and 31st - two days of massive cross-city movement and social gatherings.  We can then predict that about 400 newly infected people will be at peak infectiousness on December 31st, and that we could be looking at 3000 cases by January 8th. This is far more serious than the Crossroads hotel outbreak in July, because it has occurred during the peak festive season and we know the exact dates when super-spreading, mostly indoors, will occur. Christmas and New Year are when people mingle more than ever and attend gatherings more than ever.  So during this time, we may expect one person to infect more than the average of 2-3 other people.  The localised lockdown of the Northern Beaches may or may not work, as we have already heard of cases in other parts of Sydney.  They tried localised lockdown in Melbourne, but the epidemic had already spread beyond those suburbs.  Growing clusters in the rest of Sydney or other States may not be apparent for another week or two. Wastewater surveillance must continue to provide early warnings of hot spots.

 

If we do not act urgently, Christmas day will be a super-spreader event, with people traveling far and wide across the city, the state (and already beyond), followed by the mother of all super-spreading events, New Year’s Eve. The exhausted NSW public health team may begin 2021 with the largest COVID-19 epidemic the state has ever faced.  The happy thoughts of “living with a bit of COVID-19” and soldiering on is a falsehood, because of exponential growth of epidemic infections. Cases grow from 40 to 120 to over a 1000 in days to weeks, and the health system is the weak link in every society – it is the first part of society to break during pandemics.  When hospital and ICU beds are full, health workers dead, dying, ill or quarantined, then all other medical care becomes compromised.  If you are having a heart attack, you may not get your coronary arteries unblocked in time, and may not even get a bed.  Health workers will be in short supply. Even in the Ruby Princess related outbreak in Tasmania, over 1000 health workers were quarantined after being exposed to infected colleagues, forcing a shut down of the hospital. Every country or city that has laboured under the misapprehension that they can happily carry on with a bit of community transmission has been forced into lockdown when the health system collapsed and refrigerator trucks full of bodies were lined up at the back of hospitals.

 

So what can we do? It is still possible to prevent this predictable chain of events in Sydney.  Firstly, the testing capacity must be increased substantially – reports of people waiting in line for 5-6 hours in the last few days indicate many may lose patience and leave without testing.  Secondly, we need to rapidly ensure we have digital contact tracing methods, so that if the epidemic gets large and we cannot keep track manually, we will not fall behind. That was the biggest lesson from Melbourne. We can mandate the QR codes at every public venue, including dining, retail and entertainment and on public transport. Mandation must be accompanied by enforcement and penalties. We can also automate the data download so that all that is needed is one scan. No hanging around and filling in data on a website.  These extra steps complicate the process and decrease compliance. At the moment, it is all too easy to enter a retail or dining premise and not use the QR code, if the premise is compliant at all.  A colour coded QR code system as was used in China during the Wuhan epidemic would help – if it were mandatory for every air crew and passenger exiting Sydney airport to use the QR code and be triaged accordingly, you would not have mistakes made, such as recent arrivals who skipped quarantine and went straight to Melbourne.

 

Masks mandate across greater Sydney will make a difference, especially as people are flooding shopping malls in huge numbers for their Christmas shopping. Without a mandate, we can expect 30-50% at most to wear masks. With a mandate, it will be close to 100%. A mask mandate early in an epidemic will be far more effective than one issued at the peak, and will prevent many more infections and deaths.

 

If numbers are looking worrying in the next few days, a short, sharp lockdown (Monday to Thursday) for greater Sydney may prevent a worst-case scenario and still allow Christmas gatherings to occur. However, it’s time we provide people with instructions on safe holiday gatherings. Distorted messaging and hygiene theatre have seen people frantically washing their hands, wiping surfaces and social distancing, but unaware of other critical measures to reduce airborne transmission, which is the dominant mode of spread.  Started by WHO, unscientific and active anti-mask messaging early in the pandemic has made the policy backflips confusing for the community around the world, as countries faced with large epidemics finally turned to mask mandates when nothing else was working.  What else can people do to make the festive season safer? Restricting numbers of people at your Christmas gathering, having a backyard BBQ instead of eating indoors, keeping windows and doors open if indoors, wearing masks while not eating or drinking, and social distancing within the home. People need to be informed that home air conditioners cannot draw in fresh air, and simply recycle the air, so AC is not a solution. Church services are also high risk, as Christmas is usually the most crowded that churches become. As we did at Easter, back up plans for virtual or televised services should be made.  If services can be held outdoors, this is also an alternative. If held indoors, recorded choral music would be safest, or having singing only by the choir (with social distancing) and not the congregation. Singing generates high amounts of respiratory aerosols and there have been numerous church and choir outbreaks of COVID-19 documented. We know that breathing and speaking generate aerosols, but shouting generates much more. So the shouting of "Happy New Year" at midnight in mass gatherings is also a high risk moment that may result in super-spreading.

 

Given the high risk of indoor transmission, if this epidemic has not dwindled to single digit numbers by Christmas, we need to ban indoor mass gatherings on New Year’s Eve, including dance parties, nightclubs, pubs and restaurants. If we don’t, these businesses may face even longer closures in the months ahead, as occurred in Melbourne with a three month lockdown. 

 

Finally, we must prepare and protect our health and aged care workers. When we are ill or need care, we expect them to be there for us, so their occupational safety matters.  Over 7000 health workers had died of COVID-19 by September this year globally, and we showed that Australian health workers had 3 times the risk of COVID-19 compared to the general community.  We should not wait until 3500 of them are infected (as occurred in Victoria) before reluctantly offering them better respiratory protection.  We should be changing the guidelines now, using the precautionary principle and ensuring they are safe, well protected to face the epidemic and provide care for people. The occupational health and safety of health workers lags far behind other industries.

 

All planning must consider the exponential growth of epidemics, the role of social mixing and movement in transmission of SARS-COV-2, the calamitous timing of New Year’s Eve within 1 incubation period of Christmas day on an epidemic timeline, and the magnitude of risk this poses. At the same time, we must aim high and aim for herd immunity through vaccination, so that we do not have to face this situation again.

 

By Raina MacIntyre

Comments

Lucid, unadulterated advice. Those that ignore the implications, will simply relive historic events from the recent past.

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