Omicron Update

Author : Dr. Christopher Murray, Director of IHME

India

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New Delhi, December 22, 2021 :

How is Omicron different?

1. More transmissible and with 40-60% immune escape combine to lead to rapid increases in reported case counts.
2. A much larger fraction of infections are symptomatic – likely up from 40% for Delta and prior variants to 90-95% for Omicron
3. Based on the best available data we have, the infection-hospitalization rate is dramatically lower (note the infection-hospitalization rate is not the case-hospitalization rate), likely 90-96% lower than for Delta.
4. The infection-fatality rate is dramatically lower, likely 97-99% lower than for Delta.

How has our model changed?

1. To understand Omicron and to reflect timing of past infections, vaccinations and third doses, we have substantially revised our model.
2. Waning of immunity preventing infection and the slower waning immunity for preventing hospitalization and death are explicitly incorporated in the model.
3. Waning of vaccine-derived immunity is brand specific, Moderna has the slowest waning curve.
4. Waning of infection-derived immunity is slightly slower than vaccine-derived immunity.
5. We explicitly model ancestral, Alpha, Beta, Gamma, Delta, Omicron and other variants including the matrix of protection each type of infection gives to each other variant. 

We expect a huge increase in infections:

1. The Omicron variant is highly transmissible. We project around 3 billion infections will occur in the next 2 months. That’s as many infections as we saw in the first 2 years of the pandemic.
2. Peak transmission should be in mid-January with over 35 million global infections a day, nearly three times the Delta wave peak in April.
3. Given the immune escape and transmissibility, we extent Omicron to eventually reach all countries.  Even countries with strict border controls based on the Delta experience are likely to eventually see Omicron surges.

Detected infections (reported cases) will increase but not as much as infection:

1. Detected infections at the global level will reach 3 times previous peaks.  In the US, the peak will be over 400,000 a day. 
2. Reported cases (detected infections) will increase less than infections, because we expect the much higher fraction asymptomatic will lower the infection-detection rate.

Hospitalizations and deaths will increase much less than reported cases:

1. At the global level, hospitalizations and deaths will be lower than the prior Delta wave or Northern Hemisphere winter peak. 
2. For the US, hospitalizations and deaths will be below the Delta peak in September and well below the winter 2020/21 peaks.

Policy interventions

1. Our analysis shows that increasing mask use to 80% will have a huge effect on cases, hospitalizations and deaths.
2. More rapid and extensive delivery of third doses of vaccine will also reduce the burden of hospitalization and death. 
3. Given the rapid spread and increase in Omicron and the high fraction asymptomatic combined with much lower infection-hospitalization and infection-fatality rates, employers and schools will need to reevaluate their approach to testing and quarantine. 
4. In the future, tracking hospitalizations rather than reported cases will be a more relevant measure for local action than case counts.

Individuals can protect themselves:

1. The vaccinated getting a third dose will substantially increase protection. 
2. The unvaccinated and never infected are at greatest risk.  Vaccination for the unvaccinated is a powerful way to reduce personal risk.
3. Mask wearing remains a very effective strategy to avoid omicron transmission and infection. 
4. For those at increased risk due to age or comorbidities, avoiding indoor gatherings can further reduce risk.

Huge uncertainties:

1. There is huge uncertainty particularly about the severity of Omicron which has a critical impact on the forecasts of hospitalization and death.  More data in the next 3-4 weeks may change our view. 
2. Our more severe scenario provides a possible trajectory of data emerges suggesting the IFR and IHR is higher than the ranges we have used in our reference scenario. 
3. Based on 2020, however, data collected during the last 10 days of December and first days of January may be substantially biased.  More clarity will likely have to wait until the second week of January.
4. Currently the Omicron factors we are watching most closely are fraction asymptomatic, degree of immune escape, and severity.

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