New Danish study of about 12,000 households found that Omicron spreads faster than Delta among those who are fully vaccinated

The Omicron variant continues to spread around the world and has been reported to be three to six times as infectious as previous variants. Unlike earlier variants like Delta, Omicron has proven to cause mild symptoms and fewer hospitalizations.

However, the latest Danish study of about 12,000 households conducted in December 2021 found that Omicron spreads faster than Delta among those who are fully vaccinated than the unvaccinated.

The study, which was conducted in December 2021, included 11,937 Danish households (2,225 with the Omicron VOC), researchers discovered 6,397 secondary infections during a 1-7 day follow-up period. The SAR was 31% and 21% in households with the Omicron and Delta VOC, respectively.

According to the study conducted by researchers at the University of Copenhagen, Statistics Denmark, and Statens Serum Institut, researchers found that the Omicron variant evades the immunity of vaccinated individuals at a much faster pace compared to Delta, and at a higher rate than the unvaccinated.

However, there is also a silver lining in the study for the vaccinated. The study also found “increased transmission for unvaccinated” than those who are fully vaccinated, while there was reduced transmission between people who received booster shots.

“We found an increased transmission for unvaccinated individuals, and a reduced transmission for booster-vaccinated individuals, compared to fully vaccinated individuals. Comparing households infected with the Omicron to Delta VOC, we found an 1.17 (95%-CI: 0.99-1.38) times higher SAR for unvaccinated, 2.61 times (95%-CI: 2.34-2.90) higher for fully vaccinated and 3.66 (95%-CI: 2.65-5.05) times higher for booster-vaccinated individuals, demonstrating strong evidence of immune evasiveness of the Omicron VOC.”

To date, the variant has spread to 90 countries worldwide and has become the dominant variant in the United States. From the study:

“The Omicron VOC (variant of concern) has been reported to be three to six times as infectious as previous variants, with a short doubling time, including early estimates from countries with a high vaccination coverage indicating doubling times of 1.8 days (UK), 1.6 days (Denmark), 2.4 days (Scotland) and 2.0 days (United States).”

It’s not all bad news. Instead of putting all the eggs in the vaccine basket, the researchers also have some recommendations for the government and health officials to combat the infection. “Our data indicate that the non-pharmaceutical interventions that were used to control the previous variants of SARS-CoV-2 are also likely to be effective against the Omicron VOC.”

Meanwhile, data from highly vaccinated countries suggests that vaccinated people are at higher risk of infection from Omicron. For example, on Wednesday Denmark, a country with fewer than 6 million people or about 1/60th as many as the United States, reported 28,000 Covid infections – equal to about 1.7 million in the United States. The figures are similar in the United Kingdom, and all over Western Europe.

To date, 78 percent of Danish citizens are fully vaccinated with two doses, while almost half have received a booster shot. More than 80 percent have received Pfizer-BioNTech’s vaccine. However, the effectiveness of vaccines is reduced to around 40 percent for symptoms and 80 percent for severe disease with the Omicron variant.

With booster shots,  the effectiveness of the vaccine was reduced to 86 percent for symptoms and 98 percent respectively for those suffering from severe infection.

Below is the abstract of the study.

Abstract

The Omicron variant of concern (VOC) is a rapidly spreading variant of SARS-CoV-2 that is likely to overtake the previously dominant Delta VOC in many countries by the end of 2021.

We estimated the transmission dynamics following the spread of Omicron VOC within Danish households during December 2021. We used data from Danish registers to estimate the household secondary attack rate (SAR).

Among 11,937 households (2,225 with the Omicron VOC), we identified 6,397 secondary infections during a 1-7 day follow-up period. The SAR was 31% and 21% in households with the Omicron and Delta VOC, respectively. We found an increased transmission for unvaccinated individuals, and a reduced transmission for booster-vaccinated individuals, compared to fully vaccinated individuals. Comparing households infected with the Omicron to Delta VOC, we found an 1.17 (95%-CI: 0.99-1.38) times higher SAR for unvaccinated, 2.61 times (95%-CI: 2.34-2.90) higher for fully vaccinated and 3.66 (95%-CI: 2.65-5.05) times higher for booster-vaccinated individuals, demonstrating strong evidence of immune evasiveness of the Omicron VOC.

Our findings confirm that the rapid spread of the Omicron VOC primarily can be ascribed to the immune evasiveness rather than an inherent increase in the basic transmissibility.