Thread by @awong37

"Hi Alex, what's BA.2? Is it a little bad or is it REALLY bad?"

BA.2 is a sub-lineage of Omicron. The 'original' lineage of Omicron is designated as BA.1 & remains the dominant strain circulating in most parts of Canada currently.

A brief 🧵 of what we know thus far. /1

BA.1 & BA.2 are both classified by @WHO as Omicron, but are distinct viruses. See the phylogenetic diagram below (thx @kallmemeg).

BA.2 has over 25 mutations that differentiate it vs BA.1.

Many questions still exist around how similar BA.1 & BA.2 are clinically. /2

Danish pre-print data comparing transmission of BA.1 vs BA.2 in household settings suggests BA.2 IS more transmissible than BA.1.

BA.2 also LIKELY possess more immune-evasive properties vs BA.1 that could reduce vaccine efficacy. /3

medrxiv.org/content/10.110…

Recent @UKHSA report from Feb 16 also suggests BOTH transmissibility AND immune-evasiveness properties that drive the growth of BA.2 vs. BA.1.

Nice summary below @kallmemeg.

So STRONG evidence to support overall growth advantage of BA.2 over BA.1. /4

https://twitter.com/kallmemeg/status/1494100170195312646

Because of these growth advantages over BA.1, BA.2 WILL quickly become the dominant variant just as Omicron dominated Delta worldwide.

Graph courtesy @JeffGeeChartz below shows how BA.2 now dominates in many countries including India, Denmark, etc. /5

BA.2 has been reported across Canada, including Saskatchewan. None of this is surprising. We fully expect BA.2 to eventually dominate BA.1 across Canada.

Wastewater analysis throughout January 2022 has identified BA.2 in multiple #SK communities. /6

cbc.ca/news/canada/sa…

BA.1 was ALREADY super transmissible. BA.2 looks to be even more so. Not great.

Here are BIG clinical questions re: BA.2.

- How do vaccines protect against BA.2?
- If you've recovered from BA.1, are you protected vs BA.2?
- Does BA.2 cause MORE severe illness than BA.1?

/7

The caveat with all things #COVID19 is that data & our understanding continues to rapidly evolve.

What we think is right today, could be wrong tomorrow.

That said, right now data looks REASSURING that BA.2 is NOT worse than BA.2 clinically. /8

Recent @UKHSA data showed that serum from triple-vaccinated persons DID neutralize BOTH BA.1 & BA.2 equally well.

Also, NO difference in most recent real-world vaccine effectiveness analysis from UK for BA.1 vs. BA.2. Early times, though. /9

https://twitter.com/kallmemeg/status/1494100176465760256

Evidence base for BA.2 is very immature, so need to take this in the appropriate context, but so far UK data has shown ZERO persons infected with BA.1 who then acquired BA.2.

All reinfections w/ BA.2 occurred in persons with Alpha, Delta, or original SARS-CoV-2 strain. /10

A recent Japanese preprint on BA.2's pathogenicity in hamsters suggests possibly increased virulence vs BA.1, as well as decreased vaccine efficacy.

How this translates clinically in humans, difficult to know.

IMO, not reason for mad panic. /11

biorxiv.org/content/10.110…

Recent preprint data from South Africa provides the first CLINICAL evidence that BA.2 DOES NOT cause more severe illness vs. BA.1.

Caveats again with regards to comparing South Africa's epidemiology vs that of other settings.

Still, encouraging. /12

https://twitter.com/EricTopol/status/1495413545386713094

What about protection vs BA.2 *if* you're triple vaccinated? Or is different than protection vs BA.1?

Limited preprint data encouraging.

Neutralizing antibody responses w/ 3 doses in BA.2 were only ~1.4 times lower than BA.1, but still protective. /13

medrxiv.org/content/10.110…

Same preprint. 6 persons w/ 2 or 3 doses of mRNA & recovered from BA.1 developed neutralizing Ab responses vs BA.2 ~1.3 times lower vs BA.1, but STILL protective.

This suggests reinfection risk w/ BA.2 is VERY LOW if you have 2 or 3 doses *AND* recovery w/ BA.1.

Phew. /14

The problem is that we know that protection vs. Omicron infection wanes quickly, more so than with past variants.

Here is recent UK data showing how protection w/ 3 mRNA doses wanes vs Omicron infection over time (h/t @AdamJKucharski). /15

https://twitter.com/AdamJKucharski/status/1495334451286614018

Similarly, protection w/ 3 doses vs. severe illness & hospitalizations w/ Omicron also wanes over time, though not as significantly compared to infection.

Here is recent UK data that shows this trend vs. hospitalization.

h/t @AdamJKucharski. /16

https://twitter.com/AdamJKucharski/status/1495334456932114433

So, to summarize, BA.2:

- IS more transmissible & immune evasive vs BA.1, meaning BA.2 WILL inevitably dominate BA.1 worldwide.
- Doesn't clearly cause more severe illness vs BA.1, but data is immature.
- 3 doses +/- BA.1 recovery DOES provide significant protection vs BA.2

/17

Much credit once again goes to the superb work from South Africa (@Tuliodna & @nicd_sa) along with excellent UK surveillance for informing the world regarding BA.2 thus far.

Ongoing worldwide surveillance remains critical via PCR testing & analysis. /18

https://twitter.com/Tuliodna/status/1495419027962974209

In our local context, is BA.2 something to worry about in Saskatchewan? I'd say "maybe".

It's MORE transmissible than BA.1. With masking & other protections out the window & hospitals / ICUs still struggling, we'll likely see a prolongation OR new spike when BA.2 hits. /19

How do you protect yourself & loved ones from BA.2? Nothing new.

- Get fully vaccinated / boosted!!
- Mask appropriately indoors (ideally w/ respirator)
- Use RATs before indoor gatherings
- Upgrade ventilation / filtration
- Stay home & test if symptomatic

Be safe, all.

/end