Discover more from Your Local Epidemiologist
Omicron Update: Dec 17
Well, Omicron cases are growing really fast. Like explosive, skyrocketing, vertical growth fast. If we continue this rate of spread, I would venture to say that there is no modern day virus that has spread this fast and this far ever before.
We continue to see case growth in South Africa, although I’m convinced they’ll hit their peak soon due to several indicators (like test positivity rate and acceleration slowing). While previous waves have averaged 2 months, Omicron will hopefully result in a shorter wave due to high transmissibility and change of behavior.
Omicron in Europe is well on its way. The UK continues to breaks case records. On Wednesday, the UK reported 78,610 new cases—their biggest one-day increase on record. Then, on Thursday they broke that record again and reported 88,376 new cases. France also recorded their biggest one-day increase on record with 65,713 cases. Denmark has the highest case load they’ve ever had. In all of these places, Omicron is largely driving explosive spread, but Delta is still around too. Dr. Trevor Bedford, virologist, graphed the cases by variant type and country below.
In the United States, the latest (Dec 14) projection is displayed below. Given CDC estimated 2.9% Omicron cases on Dec 11, which was up from 0.4% on Dec 4, models suggest that Omicron will start spiking case rates between Christmas and New Years. On a national level, we will probably peak in the second week of January.
I do disagree with this graph hitting 1 million cases. We don’t have the testing capacity to record this many cases. We will run out of tests, reagents, and plastic. Lab capacity is finite. We would hit a plateau in case reporting, while the “true” cases may continue to increase.
That’s a national level. But Omicron in areas like New York is well on its way. New York/New Jersey has the highest proportion of Omicron cases in the United States (13%). We are starting to see the impact of this already. Yesterday New York reported 18,276 cases- their biggest one-day increase since January 2021. 8,318 are in New York City alone.
Why is Omicron more transmissible?
While I’m convinced from the epidemiological data that Omicron is highly transmissible, we’ve been waiting on lab data to confirm on a micro-level. The first two lab studies came yesterday.
In the first, a group of scientists in Hong Kong took human tissue from the bronchus and lung and infected it with Omicron. They measured how quickly the virus replicated compared to other variants like Delta. What did they find?
At 24 hours after infection, Omicron replicated 70 times higher than the Delta variant and the original SARS-CoV-2 virus in the bronchial tissue.
Interestingly, Omicron replicated less efficiently (10 times lower) in lung tissue than the original SARS-CoV-2 virus
This rate is important because someone is only contagious once they reach a certain threshold of virus. The quicker the virus reaches this threshold, the quicker the host (i.e. human) is infectious. While it’s important to note a petri dish isn’t a human body, this study sure corroborates the case growth we’re seeing on the ground. The second study found largely the same thing.
But this is only part of the transmissibility puzzle. Omicron is also partially escaping vaccine immunity and infection-induced immunity. At this point we’ve had more than 10 studies showing this. So, even the vaccinated (especially those with only two doses) will get infected and spread the virus.
But high case loads from rapid replication and escaping antibodies is only half the story. It’s essential that we remain out of the hospital. Immunity has positively and drastically impacted hospitalizations prior to Omicron. Below is a graph from the UK showing the fanning effect: cases differentiated from hospitalizations and deaths after vaccines were rolled out.
For those without a booster, the first line of defense is down: neutralizing antibodies aren’t going prevent infection nor transmission of Omicron. However, T-cells should still keep a lot of people out of the hospital.
Those with boosters will be most protected. That’s because boosters restimulate the immune system and increase the number of antibodies. The more antibodies we have, the more they can find the the limited landing spots on Omicron. This will decrease breakthrough cases and decrease transmission.
Boosters also generate a much broader level of immunity. In other words, boosters develop antibodies against more parts of the virus than the primary series. A lab study yesterday confirmed. The authors noted:
“The antibody response after boosting is fundamentally different than it was before. It's not just raising the level of the existing antibodies, it's doing a lot more than that. Calling the third shot a booster is oversimplifying.”
In places that don’t have boosters (like South Africa) or good booster coverage (like the United States), the question remains: How well does infection-induced immunity and two doses keep people out of hospitals? And how many people have zero protection at all?
We are seeing hospitalizations and deaths increase in South Africa, but they are at lower rates than before. In Gauteng— South Africa’s epicenter— hospitalizations are about 45% than what they were for Delta. Excess deaths are now gaining speed, but still much lower than before. On a national or global scale, a small percentage can add up quickly when we are talking about an incredibly fast moving virus.
I am increasingly concerned about older adults. Earlier this week, the Kaiser Family Foundation released a report describing severe breakthrough cases in the United States. They found that more than two-thirds (69%) of breakthrough COVID-19 hospitalizations occurred among people ages 65 and older. Given that only 52% of Americans 65+ have a booster, this population is going to have a lot of breakthrough cases. And I really hope they don’t also end up at the hospital.
0-4 year old hospitalizations
South Africa continues to report a higher rate of hospitalizations among the 0-4 year old group. A few days ago we got an update from a hospital— kids have a 20% higher rate of hospitalizations with Omicron compared to Delta.
The hospital gave important context though: “Incidental COVID19 diagnoses among children exceeded COVID19 specific admissions.” In other words, more children are hospitalized “with COVID19” (e.g. injury and test positive) than “for COVID19” (i.e. SARS-CoV-2 taking over the body). So the increase in admissions is likely reflective of high community transmission. I don’t know if this is necessarily good news, but it’s not bad news either.
Case counts are going to get very high. As high as our testing capacity can take. While the severity of disease is reduced (due to immunity or intrinsic changes, we don’t know), the mere number of infections will increase hospitalizations.
Please use a layered approach this holiday season. There are still 75 million Americans relying on the “herd” to protect them through no choice of their own. While your individual risk may be low, Omicron presents significant societal risk.
“Your Local Epidemiologist (YLE)” is written by Dr. Katelyn Jetelina, MPH PhD— an epidemiologist, biostatistician, professor, researcher, wife, and mom of two little girls. During the day she has a research lab and teaches graduate-level courses, but at night she writes this newsletter. Her main goal is to “translate” the ever-evolving public health science so that people will be well equipped to make evidence-based decisions. This newsletter is free thanks to the generous support of fellow YLE community members. To support the effort, please subscribe here: