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

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 most recent BA.2.86 update on September 15, 2023.

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What to know about BA.2.86

• The virus that causes COVID-19 is constantly changing over time. Sometimes these changes allow new variants to spread more quickly or effectively. If that occurs, the new variant may become more common relative to other variants that are circulating.
• Since CDC’s first post on BA.2.86 in August 2023, the proportion of infections caused by BA.2.86 has slowly increased. In the CDC Nowcast posted Nov. 27, 2023, BA.2.86 is projected to account for 5-15% of currently circulating variants.
• CDC projects BA.2.86 and its offshoots like JN.1 will continue to increase as a proportion of SARS-CoV-2 genomic sequences.
• At this time, BA.2.86 does not appear to be driving increases in infections or hospitalizations in the United States.
• CDC contributed to and agrees with the World Health Organization’s recent risk assessment about BA.2.86 suggesting that the public health risk posed by this variant is low compared with other circulating variants, based on available limited evidence.
• Updated COVID-19 vaccines are expected to increase protection against BA.2.86, as they do for other variants.
• As mentioned in previous updates, COVID-19 tests and treatments are expected to be effective against this variant, including its offshoot JN.1.
• It is not possible at this time to know whether BA.2.86 infection produces different symptoms from other variants. In general, symptoms of COVID-19 tend to be similar across variants. The types of symptoms and how severe they are usually depend more on a person’s immunity than which variant causes the infection.
• Regardless of what variants happen, CDC will continue to track them, working closely with partners around the world to understand how they are spreading and how they respond to vaccines and treatments.

 More information for data mavens

• On Nov. 27, 2023, BA.2.86 is being shown separately for the first time on CDC’s SARS-CoV-2 Nowcast. In previous Nowcast updates, BA.2.86 was too uncommon to be shown separately and was grouped with other BA.2 strains.
• In the most recent weighted estimates, which are directly based on observed genomic sequencing data weighted by geography, BA.2.86 comprised an estimated 1.3% of U.S. sequences, with a 95% confidence interval (a measure of uncertainty) ranging from 0.7% to 2.1%.
  • These data are from the two-week period ending October 28, 2023. See this page for a more detailed explanation of weighted estimates.
  • Before this period, BA.2.86 comprised less than 1% of U.S. sequences.
  • CDC makes Nowcast projections for variants that have been at or above this 1% threshold, which is why BA.2.86 was not shown separately before.
  • There are SARS-CoV-2 sequences available for more recent weeks, but using those data can lead to less reliable projections because of differences between which sequences are submitted earlier compared with later. There is an inherent lag in the time it takes to receive specimens for sequencing, do the sequencing, and analyze and report the results.
  • CDC analyses have shown that using more complete sequencing data, even if older, provides a more accurate Nowcast than more recent, partial data.
• In CDC’s Nowcast, which forecasts the current situation (i.e., “now”) based on the older, weighted estimates, BA.2.86 is projected to comprise between 5-15% of currently circulating variants in the United States.
  • Currently, our best estimate indicates about 9% of circulating viruses may be BA.2.86.
  • These numbers are based on a relatively small number of BA.2.86 sequences, so should be interpreted with caution, as should BA.2.86 growth rates and other extrapolations based on these numbers.
  • It is important to note that early projections tend to be less reliable, since they depend on examining growth trends of a smaller number of sequences, especially as laboratory-based testing volume for SARS-CoV-2 has decreased substantially over time. For this reason, this projection may be revised as more data become available in future weeks.
• In these estimates and projections, offshoots of BA.2.86, including JN.1, are grouped with BA.2.86. JN.1 is still below the 1% threshold in weighted estimates, which is why it is shown grouped with BA.2.86.