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Difficulty in sustaining Zero Covid in 2022

Source: Peng et al. 2023 SSRN https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4317640#

In a Zero Covid strategy, it’s preferable to stay at zero daily cases as much of the time as possible

In 2021 (Delta), most parts of China had zero daily cases most of the time

In 2022 (Omicron), increasing incidence of outbreaks, requiring on average twice as long to control

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Incidence of infections in past 2 months

Peak in late Dec with minimal control measures – epidemic ended after running out of susceptibles
Inactivated vaccines do not prevent COVID infection (except for during a short time after receiving a dose), and very few vaccine doses have been administered in recent months
High transmissibility of Omicron (overwhelming even stringent Zero Covid measures)
THEREFORE likely that more than 80% of population infected, perhaps much more than 80%

Source for peak in late Dec: https://en.chinacdc.cn/news/latest/202301/t20230126_263523.html

Source for low vaccine effectiveness against infection unless recently jabbed: Tsang et al. 2023 Lancet Infect Dis

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Omicron severity – observations from HK

In Hong Kong’s large wave in early 2022 – around 4 million BA.2 infections and 10,000 deaths = 2.5 deaths per 1000 infections, but most of those deaths occurred in unvaccinated older adults which comprised a much smaller fraction of the population
In Hong Kong’s large wave, case fatality rates increased 3x during the peak, perhaps because of limited healthcare resources at that time

We estimate similar intrinsic severity of Omicron to the original Wuhan strain, where in unvaccinated older adults the risk of mortality was around 1%-5%

Unpublished data on severity in Hong Kong

Various estimates of Wuhan strain infection severity are available in the literature

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Vaccine effectiveness in HK vs severe Omicron BA.2

McMenamin et al. 2022 Lancet Infect Dis

This analysis is for effectiveness of mostly recent second doses and recent third doses because of the timing of vaccinations and Omicron spread in HK

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Mortality in recent wave – general observations

For adults ≥60 years, cumulative vaccination rates for first, second, and third doses were reported as 90.7%, 86.4%, and 68.8%, respectively, as of 28 November 2022.

25 million unvaccinated
57 million with only a first dose or second dose (mostly not recent) but not a third dose

If >80% infected among these 82 million people and a CFR of >1.5% (?), mortality would exceed 1 million
Then think about the impact of crowded hospitals on care of COVID patients, and other patients

Source for vaccine uptake: http://www.nhc.gov.cn/xcs/s3574/202211/6fedb556a9324cd3b5b986446ee7ca34.shtml

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COVID mortality – NYT

Source: https://www.nytimes.com/interactive/2023/02/05/world/asia/china-obits-covid.html

All-cause mortality rate of a group of 1700 eminent scholars (typically older adults) increased by a factor of 4-5 in Dec and Jan

One estimate I have seen is that there were around 10.4 million deaths in China in 2022 overall (?) which is 860,000 per month

Even a doubling of monthly mortality for two months, nationwide, would correspond to an excess of 1.7 million deaths (just for reference, not an estimate)

Note that excess mortality this winter would not only be due to COVID infections but also due to disruption of the emergency care pathway for other conditions (e.g. strokes)?

Excess above baseline

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Population immunity

When talking about population immunity it's important to distinguish immunity from infections versus immunity from severe disease

Vaccination doses and infections provide short-lived boosts in immunity against infection, but this wanes, partly because the virus continues to evolve, and new strains can escape from existing immunity.

Vaccination doses and infections provide longer-lasting immunity against severe disease.

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Whats next?

COVID fairly unpredictable
Next peak perhaps in 4-6 months? Could be earlier, unlikely to be as synchronized nationwide as the just-finished wave
Infections will have lower average severity because of higher population immunity against severe disease, some mortality will still occur in older adults and particularly those not recently vaccinated

as an illustration

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