Saturday, September 16, 2023

CDC COVID Nowcast & BA.2.86 Update


Just over a year ago, the CDC Nowcast from late August of 2022 (see below) featured 1 hugely dominant variant (BA.5), and a short list (n=3) of rising and falling competitors (BA.4.6, BA.4, BA.2.12.1).  

As we discussed a couple of weeks ago in Viral Anarchy, over the past 12 months we've seen a 6-fold increase in the number of circulating variants in the United States. 

And we've not seen a truly dominant variant in months, after the sharp decline of XBB.1.5 over the summer. 

Today, due to the explosion of recombinant (XBB) variants and their offshoots, the CDC is tracking over 25 variants circulating in the United States, including at least one (i.e. BA.2.86) which doesn't even appear on the Nowcast chart.  

For now, EG.5 at 24.5% is the largest contributor to the COVID pool, and while HV.1 (in 5th place) has shown a 40% increase over two weeks ago, there are no hugely dominant contenders for the viral throne.  Unless and until that changes, this viral diversity is likely to continue. 

Our current surge in infections and hospitalizations is likely driven by a combination of factors, including waning community immunity, and a smorgasbord of EG, XBB, and FL variants.  The good news is, most should be at least partially mitigated by the new XBB.1.5 based vaccine. 

But in the wings, there is a potential wildcard; BA.2.86, which boasts the largest number of mutations we've seen since the emergence of Omicron nearly 2 years ago. Despite the huge amount of hype it has received over the month, its impact so far appears to be small, and its future is far from assured. 

That doesn't mean we can afford to ignore it.  It is still reorganizing itself, picking up small mutations as it spreads, and it - or its descendants - still have the potential to be game changers. 

But first, it has to out-compete the plethora of variants already in circulation, and we've not seen clear evidence of that happening.  Nor do we know whether it will be more - or less - severe (or immune evasive) than existing Omicron variants. 

The CDC continues to monitor the variant, even though it isn't prevalent enough to show up on the bi-weekly Nowcast.  Late yesterday afternoon the CDC posted the following update:

Update on SARS-CoV-2 Variant BA.2.86 Being Tracked by CDC

September 15, 2023, 3:00 PM EDT
CDC is posting updates on respiratory viruses every week; for the latest information, please visit CDC Respiratory Virus Updates.

CDC is tracking a SARS-CoV-2 variant called BA.2.86 and working to better understand its potential impact on public health. This update follows CDC’s previous BA.2.86 update on September 8, 2023.

Moving forward, we will share updates on BA.2.86 when significant additional information becomes available. It is anticipated that this will be our last routine weekly update for this variant.

Read about CDC’s recommendations for updated COVID-19 vaccines, and learn more about ways to keep you and your loved ones safe as we head into the fall and winter respiratory virus season.

What’s New?
  • During the Advisory Committee on Immunization Practices meeting on September 12, 2023, manufacturers of the 2023-2024 COVID-19 vaccines presented laboratory evidence demonstrating that their vaccines are expected to provide protection against the virus that causes COVID-19, including the BA.2.86 variant.
  • At this time, BA.2.86 does not appear to be rapidly increasing or driving increases in infections or hospitalizations in the United States.
  • There are likely low levels of community transmission of BA.2.86 occurring within several countries, including parts of the United States. We are concluding this because some of the people infected with BA.2.86 do not have known links to other infected individuals and did not recently travel to an area with known cases of illness from BA.2.86.
  • It is unclear how easily BA.2.86 spreads compared to other circulating variants. An investigation of a recent outbreak in a long-term care facility in the United Kingdom showed that, like other variants, transmission can occur in congregate settings.
CDC will continue monitoring BA.2.86 and other circulating variants of the virus that causes COVID-19.

The remainder of CDC’s assessment remains unchanged from the September 8 update.

The late summer surge in COVID is difficult to quantify, given the dismantling of testing, surveillance, and reporting of cases (including hospitalizations and deaths).  For the 6th week running, there are huge swaths of the country not reporting enough data to be utilized in the Nowcast (see map below)

Anecdotally, I'm hearing of a lot of cases here in Florida, including two of my relatives, who - due to their age and comorbidities - are having a rough time of it.  While many people may be lucky enough to only experience mild-to-moderate illness, for some people this remains a life-threatening disease.

As to what the fall will bring, yesterday the CDC released a preliminary 2023-2024 Respiratory Disease Season Outlook, which anticipates a similar number of hospitalizations to what we saw last winter.

But they are quick to point out, there are a lot of unknowns, including the future impact of BA.2.86. Which is why they are only attaching a low-to-moderate level of confidence to this early assessment.