Quick nowcast and forecast on situation awareness of HK Covid 5th wave…1/n
Since beginning of 5th wave, there have been about 1.7 (0.32 – 2.86) million people already infected as of February 28, 2022…2/n
We expect this wave to peak in the coming week or so, at 182,738 (36,794 – 263,300) new infections per day or 35,121 (9,985 – 46,091) newly reported cases per day…3/n
The lagged daily number of deaths is projected to peak around 156 (46 – 184) by mid-March and the cumulative number of deaths by the end of April could be as high as 4,645 (3,143 – 5,568)…4/n
Estimates of death assume: 1) our health system surge capacity continues to be overwhelmed, 2) there is no dramatic and rapid improvement in vax coverage amongst institutionalised elderly, 3) no immediate and widespread novel antivirals (e.g. Paxlovid or molnupiravir) use…5/n
Spread will speed up if PHSMs were to be relaxed before April. If virus is not locally eliminated by late April, ongoing PHSMs with at least 35% reduction in social mixing would be needed to prevent case numbers from resurging albeit unlikely at currently observed levels…6/n
Therefore, if compulsory universal PCR testing were to be implemented under “dynamic zero-covid policy”, it should be deployed mid- to late-April when case numbers will already be at very low levels in order to truly achieve elimination, or “zero covid”…7/n
Doing so earlier, especially when case numbers will still be too high to properly and appropriately isolate and care for, paying particular attention to population mental and emotional wellbeing in HK’s unique context, would not be recommended…8/n
Another update on HK’s Omicron BA.2 (“5th”) wave nowcast and forecast (we’ve made some important methodological improvements - see med.hku.hk/en/news/press/… for full details)…1/n
5th wave has peaked on March 4. Estimated no of people infected by March 7 = 1.8M (1.0-2.7M). No of daily infections to fall below 1,000 by end Apr and to below 100 by mid May…2/n
Final size of 5th wave ~4.3M (3.8-4.7M) infections and ~5000 deaths…3/n
HK has almost no natural immunity. We estimated ~1% had prior infection. We skipped over alpha and delta, unlike many other places around the world. We are experiencing Omicron BA.2 - the most transmissible VOC to date (R0 >3x ancestral strain) with +++ immune escape potential.
In addition, during the exponential surge, one would expect to observe the very frail and vulnerable succumb first. Prelim data shows onset-to-death interval shrunk from 18d (average of HK’s first 4 waves of the ancestral strain) to around 6d (current Omicron BA.2 wave).
“...infectiousness only started to rise substantially 5-6 days before symptom onset, around the average time of infection assuming an incubation period of about 6 days...”
“...only <0.1% of transmission would occur before 7 days, 1% before 5 days and 9% before 3 days prior to symptom onset...”