Unvaccinated people are at more risk of catching BA.2, the new Omicron lineage, than any prior type of COVID-19, Danish data indicates

Unvaccinated people are at more risk of catching BA.2, the new Omicron lineage, than any prior type of COVID-19, Danish data indicates
A person receives a COVID-19 test in New York City on December 15, 2021.David Dee Delgado/Getty Images
  • A Danish household study suggested that Omicron BA.2 is even better at spreading than BA.1.
  • Unvaccinated people are likely at the highest risk, the study suggests.

The emerging subvariant of Omicron, BA.2, is even better at spreading than Omicron BA.1, a study of households in Denmark suggests.

Unvaccinated people were at the highest risk of both catching and passing on the subvariant, per data collected by Danish officials and shared with Insider.

Fully vaccinated and boosted people were also more likely to catch BA.2 than BA.1, but they were less likely to transmit it to someone else.

"We feel quite confident that BA.2 must be more transmissible to some extent," Dr. Camilla Holten Møller, the head of the SSI's expert group for COVID-19 modeling, told Insider.

"The good news is that we do see an effect of vaccination."


The fastest

The results suggest that Omicron BA.2 is the most transmissible of the major types of coronavirus seen so far, given that BA.1, since BA.1 was already known to be more transmissible than prior variants like Delta and Alpha,

The study, led by Denmark's leading public health body the Statens Serum Institut (SSI), was published on pre-print server medRxix on Sunday and has not been peer-reviewed.

Using health data from about 8,500 Danish households, the study looked at how likely people were to test positive within seven days of one of the members of the household catching either BA.1 or BA.2.

It ran from December 20, 2021 to January 11. It did not focus on the symptoms of disease, only on whether the participants tested positive.

BA.2 is not thought to cause more severe disease than BA.1, the Danish health ministry has said.


The first set of data compared households that caught BA.1 to those that caught BA.2, and showed BA.2 spreading more quickly.

When exposed to someone with BA.2, household members were two to three times as likely to catch it as BA.1, regardless of whether they were unvaccinated, fully vaccinated, or boosted, the study found.

However, unvaccinated people were 2.6 times as likely to pass on BA.2 as BA.1. Fully vaccinated and boosted people were less likely to pass it on.

The second set of data also suggests the subvariant spreads more easily among unvaccinated people. It looked only at households that were infected with BA.2 and split the data by vaccination status.

Here's the data:

  • Unvaccinated: about 10% more likely to catch the coronavirus from someone with BA.2 than the fully vaccinated household members, and about 20% more likely to pass it on
  • Boosted: about 20% less likely to catch it than fully vaccinated (two doses), and about 20% less likely to pass it on.

There was some overlap in the confidence intervals between fully vaccinated and unvaccinated groups in this dataset. That means that the difference between these two groups was not statistically very solid, so could change with more data.

It's unclear how bad BA.2 is

BA.1 still makes up more than 98% of infections worldwide, the SSI reported Wednesday. But it outcompeted BA.1 in Denmark in January, causing the country to investigate whether it is inherently more transmissible.

Last Wednesday, the SSI reported that BA.2 spread about 1.5 times more quickly than BA.1 in Denmark.

Hospitalization rates of people with COVID-19 have been rising. But Møller told Insider that Denmark was seeing more people being admitted for other reasons who happen to have COVID-19 than in previous waves.

It's too early to know for sure how much protection the vaccines are offering against severe disease and death from BA.2.


Early data from the UK Health Security Agency published Thursday suggested that boosters greatly reduce the rate of symptomatic disease against BA.2, by about 70%, whereas two doses only reduced that rate by about 13%.

This is comparable to rates seen with BA.1.