Avian Flu Diary: Denmark SSI: Omicron Variant BA.2 Rising - Expected To Soon Comprise 100% Of Cases

COVID Infection Rate 6 Times Higher In Denmark than UK & UK -

Credit Our World In Data

#16,546

Although the United States and the UK have endured a steep rise in COVID cases over the past 60 days due to the emergence of the Omicron variant, their experiences pale in comparison to Denmark, which right now is reporting an infection rate (per million people) 6 times higher.

These numbers are based on officially reported test results, and likely under represent the true incidence in all three nations.

Today, Denmark's SSI announced that based on a relatively small blood donation analysis, one in three adults has likely been infected since November (see Every third adult Dane has probably been infected since November).

Denmark - unlike most of the rest of the world - is dealing with a new subvariant of Omicron, dubbed BA.2. Four days ago, in Preprint: Transmission of SARS-CoV-2 Omicron VOC subvariants BA.1 and BA.2: Evidence from Danish Households, we looked at a study suggesting BA.2 was substantially more transmissible than the globally dominant BA.1.

Today Denmark's SSI projects BA.2 will supplant BA.1 by the middle of the month, and that will likely delay the expected decline in cases.

Assuming BA.2 performs similarly in other countries, that could have serious ramifications for nations outside of Denmark which currently appear to be seeing a decline in cases.

First, the summary report from Denmark's SSI, followed by some (translated) excerpts from their latest Risk Assessment.

(Translated)

The omicron variant "BA.2" outperforms "BA.1". It is soon expected to be up to 100% in Denmark

The prevalence of the omicron variant BA.2 continues to increase in Denmark. It became dominant in week 2 and accounted for 69% in week 3. BA.2 is expected to account for up to 100% of infections in mid-February 2022.

Last edited on February 3, 2022

The Statens Serum Institut (SSI) has prepared a risk assessment for the omicron variant BA.2 (pdf).

BA.2 has a higher growth rate than BA.1

The preliminary projections show that the growth rate for BA.2 is significantly higher than for BA.1. This equates to BA.2 being approximately 30% more contagious than BA.1.

This means that the emergence of BA.2 may lead to a steeper epidemic curve with a higher peak for the number of daily cases of infection. Similarly, BA.2 may postpone the time of the expected decline in infection until into February.

Read more in the note Growth rates for the omicron variants BA.1 and BA.2 (pdf)

BA.2 is more contagious than BA.1

A new Danish study from SSI, the University of Copenhagen and DTU shows that BA.2 is more contagious than BA.1.

The study shows that if a person in your household is infected with BA.2, there is generally a 38% risk that another household member will be infected within the first week. If, on the other hand, the person is infected with BA.1, the risk is 29%.

The study is based on 8,541 households with 17,945 other residents in the period from 20 December to 18 January.

It also shows that the risk of becoming infected is highest for unvaccinated compared to vaccinated for both BA.1 and BA.2. However, vaccinated people have a relatively higher risk of becoming infected with BA.2 compared to BA.1.

Read the entire new study (pdf)

From the 7-page Risk Assessment Risikovurdering af omikron BA.2 - den 28. januar 2022:

Conclusion
The incidence of the Omikron variant BA.2 continues to increase, and the variant has now become dominant. BA.2 is expected to account for up to 100% of infections in the middle of February 2022, as the growth rate for BA.2 is significantly higher than for BA.1, corresponding to approx. 30% more contagious.

This means that the emergence of BA.2 may result in a steeper epidemic curve with a higher peak for the number of daily cases of infection, just as BA.2 can postpone the time of the expected decrease in infection until into February.
Preliminary data show that BA.2 infects a higher proportion of members in a household than BA.1, which supports that BA.2 has a higher infectivity than BA.1. Unvaccinated are significantly more contagious if they are infected with BA.2 compared to BA.1, where the reverse is true the case of the vaccinated. At the same time, vaccinated individuals are generally seen more susceptible to BA.2 relative to BA.1, but there is a lower risk of transmission.
There is still no evidence that BA.2 is associated with an increased risk of hospitalization.
SSI is in the process of trying to grow BA.2 in order to make antibody neutralization studies, but it has been shown to be very difficult to grow.
It is still relevant to follow the variant closely and make / continue supplementary studies of variant properties (eg antibody neutralization studies and vaccine efficacy). It is recommended on a current basis that infection detection BA.2 on same level as the other variants.

While making predictions about what COVID will do next is admittedly a mug's game, it is hard to see how Denmark's experience won't be duplicated in many other countries around the globe over the next few months.