Thread by @DrTomFrieden

What are the facts on Omicron? The picture is getting clearer: Omicron spreads faster and is better able to escape immunity than other variants. Severity is still unknown, although it's likely vaccination reduces severe disease. The virus has adapted; we must as well. 1/thread

Today’s technical briefing from @UKHSA has a wealth of info. Encouraging to see quick research and action from scientists and health agencies in South Africa, UK & other places, and CDC. Too little credit often given for great work under great pressure. bit.ly/31QLILV 2/

Omicron will almost certainly overtake Delta and cause new waves of infection globally. This happened within weeks in South Africa. In the UK, Omicron cases are projected to reach parity with Delta by mid-December, according to the briefing, and are doubling every 2-3 days. 3/

What does this mean? Omicron spreads FAST. Studies of household contacts find a higher risk of transmission—more than double—when index case is caused by Omicron than when it is caused by Delta. That’s a striking finding. 4/

https://twitter.com/kallmemeg/status/1469352389706719234

To avoid infection, we have to be very careful in the weeks ahead. Several reports, including from a Christmas party outbreak in Oslo, indicate that the variant can infect with ease. bit.ly/3pT4daW 5/

Emerging data indicate that Omicron evades immunity to some degree and causes infection in people who have already had Covid and/or been vaccinated. 6/

Vaccines provide excellent protection against severe disease caused by other variants and that will likely be the case for Omicron—but we can’t be certain yet. As with so many important questions: patience, rigorous analysis, and understanding that it’s too soon to say. 7/

Across five preliminary studies on how antibodies from fully vaccinated people fare versus Omicron, there was 20-40X reduction in neutralization of the virus compared to earlier variants. Antibodies aren't the only indicator of protection, so we have to await real-world data. 8/

Unfortunately, four months after primary series AstraZeneca vax offered no protection from infection with Omicron and effectiveness of Pfizer vaccine waned quickly & dramatically, according to @UKHSA technical brief—but more important question is protection vs. severe disease. 9/

But the good news is that an mRNA booster dose resulted in an increase of protection irrespective of primary vaccination type. After two weeks of a Pfizer booster, vaccine effectiveness was restored. 10/

This is a small but striking sample that points to how evasive Omicron may be. 11/

https://twitter.com/EricTopol/status/1469295967019036672

It’s not only vaccine protection that Omicron is eroding—it’s also infection-induced immunity. Omicron poses about a 5X greater risk of reinfection than Delta among people who have had Covid previously. Get vaccinated as soon as possible, and get boosted when you’re eligible. 12/

Omicron MAY be less severe—we don’t know yet. @nataliexdean has a great explanation of one reason why determining severity is complex. This will take time to figure out, but we can’t wait for definitive data to act. 13/

https://twitter.com/nataliexdean/status/1468988174693289994

A note of caution: the characterization of Omicron from this early data will evolve, but early data can provide clues, and it’s helpful to monitor so we can prepare as well as possible. We’ll continue to learn more in the days ahead. 14/

Bottom line: Omicron poses a serious threat but we’re not back to square one. We’ve got vaccines, masks, tests, treatment, ventilation. Get vaccinated and boosted, mask up indoors, test if exposed or sick, modulate activities based on risk and how much Covid is spreading. 15/

Let’s learn from the lesson of Omicron—this virus moves fast. Mutations are in effect innovations by the virus. To keep up and blunt disease spread and deaths, we need to learn quickly, communicate well, and act effectively. 16/end