Weekly epidemiological update: Omicron variant of concern (VOC) – week 2 (data as of 20 January 2022) EU/EEA

Epidemiological update

As of 20 January 2022, the Omicron variant has been identified in all EU/EEA countries. From 20 December 2021 to 9 January 2022, there were 23 EU/EEA countries with adequate sequencing volume that reported an estimated prevalence of Omicron VOC of 69.4%. Across studies from various settings, the risk of hospitalisation has been found to be lower for Omicron than for the Delta VOC. However, prior immunity from natural infection, vaccination including booster doses, and improved treatment options contribute to less severe outcomes, making it challenging to estimate the inherent risk of severe infection for Omicron. While studies have used slightly different data, analysis approaches and adjustments for confounding factors, most studies found risk reduction in the range of 50-60%. Still, among Omicron cases reported to TESSy, 1.14% were hospitalised, 0.16% required ICU admission/respiratory support, and 0.06% died. Early studies suggest that current vaccines may be less effective against Omicron infection, although they still provide protection against hospitalisation and severe disease. Given the exponential growth advantage of Omicron and the high numbers of cases, any potential benefits of a lower observed severity can be outpaced by the sheer number of severe outcomes over time.

This weekly epidemiological update provides an overview of the extent to which SARS-CoV-2 Omicron VOC is prevalent in EU/EEA countries, based on the best currently available evidence (as of 20 January 2022). The data are collected from The European Surveillance System (TESSy) or the GISAID EpiCoV database. Please refer to the ECDC Variants of interest and concern in the EU/EEA dashboard for more details. In cases of missing data, EU/EEA countries’ official national or regional websites are used, which are linked to the country name below. As a result, the data presentation and completeness might be different depending on the data sources and availability.

As of 20 January 2022, the Omicron variant has been identified in all EU/EEA countries. From 20 December 2021 to 9 January 2022, 23 EU/EEA countries with adequate sequencing volume reported an estimated prevalence of Omicron of 69.4% (range from 5.7% to 99.9%), over 20% higher than in the previous week.

Countries where Omicron has become the dominant variant (accounting for more than 50% of sequenced viruses) include Austria (95.4%, 2022-02), Belgium (99.7%, 2022-02), Cyprus (93.9%, 2022-01)*, Czechia (66.7%, 2022-02), Denmark (98.8%, 2022-02), Finland (99.9%, 2022-02), France (90.8%, 2022-02), Germany (62.5%, 2022-01), Greece (85.6%, 2022-01), Hungary (64.7%, 2022-02),  Iceland (90%, 6 January 2022), Ireland (89.2%, 2021-52)*, Italy (81%, 2022-01), Liechtenstein (88.5%, 2022-01)**, Lithuania (40.5%, 2021-52)*, Luxembourg (89.6%, 2022-01), Malta (99.3%, 2022-01)*, the Netherlands (95.3%, range between labs 93.3% - 98.6%, 10 January 2022), Norway (93.8%, 2022-02), Portugal (86.3%, 2022-01), Slovenia (67% of cases sequenced on 5 January 2022), Spain (87.4%, 2022-01), and Sweden (91.8%, 2022-01).

Countries where the Omicron variant is present but not dominant include Bulgaria (43.5%, 2022-02), Croatia (no national proportion available), Estonia (45.8%, 2022-02), Latvia (5.8%, 2022-02), Poland (26.2%, 2022-02), Romania (37.8%, 2022-02), and Slovakia (29.9%, 2022-02).

Large (20% or higher) increases in the number of cases since last week have been reported in the following countries: Bulgaria, Cyprus, Czechia, Estonia, Germany, Hungary, Italy, Luxembourg, Malta, Spain, and Sweden. For a general overview of the epidemiological COVID-19 situation in the EU/EEA, please see the ECDC weekly Country Overview ReportECDC Country Overview Report.

Based on case-based data, 155 150 Omicron cases were reported to TESSy between weeks 2021-46 and 2022-02 from: Austria (number of cases 84 537; proportion of all cases 54%), Cyprus (343; 0%), Estonia (27; 0%), Finland (8 149; 5%), Ireland (1 404; 1%), Italy (3 231; 2%), Liechtenstein (35; 0%), Luxembourg (974; 1%), Malta (296; 0%), Norway (50 534; 33%), Poland (37; 0%), Portugal (570; 0%), Romania (92; 0%), Slovakia (112; 0%), and Sweden (4 809; 3%).

  • The median (interquartile range) age of these Omicron cases was 30 (20–33) years, 7% were aged 60 years and above, and 50% were male.
  • Among 111 946 (72%) Omicron cases with complete data on symptom status, 84 662 (76%) cases were reported as symptomatic and 27 284 (24%) as asymptomatic.
  • Complete data on vaccination status were available for 2 369 (2%) Omicron cases, among which 211 (9%) were reported as one dose, 1 646 (69%) were reported as two doses, 255 (11%) were reported as three doses, 239 (10%) were reported as unvaccinated, and 18 (1%) were reported as vaccinated (unknown doses).
  • Among 124 849 (80%) Omicron cases with complete data on importation status, imported or travel-related cases accounted for 9 159 (7%) cases and 115 690 (93%) cases were locally acquired.
  • Among Omicron cases with known outcomes, 884 (1.14%) were hospitalised, 120 (0.16%) required ICU admission/respiratory support, and 48 (0.06%) died. The status of COVID-19 outcomes was known for 77 233 (50%) cases for hospitalisation, 76 744 (49%) for ICU admission/respiratory support, and 81 912 (53%) for death (some incomplete reporting of these variables is expected for more recent cases).

*Insufficient precision at less than 5% prevalence (more information available here).

** Seven-day average. Please note that the data for Liechtenstein are reported together with Swiss data.

Disease severity related to Omicron

Evidence from a variety of settings suggests that infections with the Omicron VOC have a less severe clinical presentation than those due to the Delta VOC. It is important to highlight that lower age, prior immunity from natural infection, vaccination including booster dose, and improved treatment options will contribute to less severe outcomes from subsequent infection. Therefore, the true risk of severe infection for Omicron may be underestimated by the large numbers of vaccinated or previously infected people, which was not the case in the beginning of preceding waves. Most studies do not account for waning immunity, or for the likely large amount of under-ascertained reinfections. This could lead to an underestimation of severity.

Among Omicron cases with known outcomes reported to TESSy as of 19 January 2022, 884 (1.14%) were hospitalised, 120 (0.16%) required ICU admission/respiratory support, and 48 (0.06%) died. The pattern of higher rates of hospitalisation, ICU admission, and death with increased age is apparent for Omicron cases, as it has been for Delta and previous variants. Similarly, low hospital admission rates (0.3%) and case fatality (<0.1%) for Omicron cases have been observed in Canada, and in Texas, California, and Denmark a shorter median length of hospital stay and/or significantly reduced need for respiratory support were reported for Omicron. This observed severity in TESSy data and in the studies cited is at least partially likely due to the protective effect of vaccination, time since vaccination, co-morbidities, and/or previous infection in some of the individuals and does not necessarily reflect the inherent severity of Omicron.   

Across studies from various settings, the risk of hospitalisation was found to be lower for Omicron than for Delta or other previous variants. While studies used slightly different data, analysis approaches, and adjustments for confounding factors, most studies found risk reduction in the range of 50-60%.

Preliminary analysis of case-based data submitted by 15 EU/EEA countries to TESSy between week 46-2021 and week 02-2022 was performed to compare the overall adjusted odds ratio (aOR) of hospital admission for infection with Omicron compared to infection with Delta among symptomatic cases. Logistic regression models adjusted for age group, sex, preconditions, reporting country, reporting week and vaccination status showed that Omicron infection was less likely to be reported with admission to hospital compared to infection with Delta (aOR 0.41; 95% CI: 0.37-0.46). More in-depth analysis will be performed over the course of the upcoming weeks to better assess the impact of Omicron on severe outcomes reported to TESSy.       

A Danish observational cohort study of 188 980 SARS-CoV-2 positive individuals during November-December 2021 compared the risk ratio of admission for Omicron compared to Delta infection and stratified by vaccination status and found that Omicron was associated with an adjusted RR of hospitalisation of 0.64 (95% CI: 0.56-0.75) compared to Delta infection. RR was 0.57 (95% CI: 0.44-0.75) among cases with none or one vaccination, 0.71 (95% CI: 0.60-0.86) among two-dose vaccinated, and 0.50 (95% CI: 0.32-0.76) among three-dose vaccinated. Similarly, Omicron had lower risk than Delta cases with regard to vaccination status, age, comorbidity, and reinfection. The lower hospitalisation risk for Omicron cases among both vaccinated and unvaccinated individuals suggests a reduced severity of Omicron, but Omicron patients in this study were younger and had fewer comorbidities than those with Delta.

In the United Kingdom, after adjusting for sex, age, travel, vaccination status and, where ascertained, previous infection, presentation to emergency care or hospital admission with Omicron was approximately half of that for Delta (Hazard Ratio 0.53, 95% CI: 0.50 to 0.57). They also found a 65% lower hospitalisation risk for Omicron cases who had received two doses of a vaccine and 81% reduction with three doses, compared to unvaccinated Omicron cases.

In Scotland, symptomatic individuals who were S-gene negative (a proxy for Omicron infection) had a two-thirds reduced hospitalisation risk compared to S-gene positive (Delta) cases, while the rate of possible reinfection for Omicron was 10 times that of Delta. People who had received three vaccine doses had a 57% (95% CI 54-60) lower risk of experiencing symptoms following Omicron infection compared to Delta.

In Southern California, the United States, the risk of hospital, ICU admission, and mortality were 0.48 (0.36-0.64), 0.26 (0.10-0.73) and 0.09 (0.01-0.75) higher, respectively, among cases with Omicron infection compared to cases with Delta infection.

It usually takes several weeks for the accumulation of clinical outcomes to make conclusions on the impact of a specific variant on hospital admissions, intensive care needs, and death rates. It is also essential to account for the relatively young age of most people who have been infected with Omicron to date, and thus far there are little data on the severity among older age groups and people with underlying risk factors. As a result, the clinical profile of Omicron may change as other groups are infected and followed over time.

Significantly, the combination of a higher growth rate and immune evasion indicate that any potential advantage Omicron may have in terms of decreased severity might be countered by increased community infection rates that lead to a substantial additional burden for hospitals, while primary care may be overburdened even more than in previous waves. As more evidence builds up, a better assessment of clinical outcomes and long-term consequences, such as post-COVID-19 condition, will be feasible.

Vaccine effectiveness against infection and/or severe disease due to Omicron

A recent (pre-print) study from Denmark estimated the transmission dynamics following the spread of Omicron within Danish households during December 2021. The study found the Secondary Attack Rate (SAR) to be 31% and 21% in households with the Omicron and Delta variants, respectively. Unvaccinated potential secondary cases experienced similar attack rates in households with the Omicron and Delta variants (29% and 28%, respectively), while fully vaccinated individuals experienced secondary attack rates of 32% in household with Omicron and 19% in households with Delta. For people who had received a booster dose, Omicron was associated with a SAR of 25%, while the corresponding estimate for Delta was 11%. There was an increased transmission for unvaccinated individuals, and a reduced transmission for booster-vaccinated individuals, compared to fully vaccinated individuals. Comparing households infected with Omicron to Delta, the study found a 1.17 (95% CI: 0.99-1.38) times higher SAR for the unvaccinated, 2.61 times (95% CI: 2.34-2.90) higher for the fully vaccinated, and 3.66 (95% CI: 2.65-5.05) times higher for booster-vaccinated individuals, indicating immune evasiveness of the Omicron variant.

The United Kingdom’s Health Security Agency (UKHSA) provides regularly updated estimates of vaccine effectiveness against symptomatic infection with Omicron, and has reported estimates of 63% (95% CI: 59%, 67%), 68% (95% CI: 55%, 78%), and 25% (95% CI: 1%, 43%), in the initial period (two to four weeks) after primary vaccination with Comirnaty, Spikevax and Vaxzevria, respectively. From 25 weeks after the second dose, the vaccine effectiveness decreased to low or non-significant levels but was restored after a booster dose of Comirnaty to 69% (95% CI: 67%, 70%) for those who had received a primary course of Comirnaty, and to 64% (95% CI: 63%, 66%) for those who had received Vaxzevria as primary vaccination. UKHSA has also conducted a separate analysis of individuals aged 65 years and older and found that, in all periods after vaccination, effectiveness was lower for Omicron compared to Delta. From 20 weeks after the second dose of either Vaxzevria or Comirnaty, minimal or no effect against mild disease was seen for the Omicron variant. Although a booster dose of either Comirnaty or Spikevax temporarily increased the protection, this also waned with time, to around 30% vaccine effectiveness against mild disease at 10+ weeks following a booster dose.

A preprint of a study from Canada assessing the vaccine effectiveness of mRNA vaccines found that two doses of an mRNA vaccine were unlikely to protect against Omicron infection (VE 6%, 95% CI: -25, 30%). A third dose provided some protection against Omicron infection (VE 37% (95% CI: 19%, 50%) in the immediate term but substantially less than against Delta (VE 93% (95% CI: 92%, 94%), ≥7 days after third dose. The study highlights that the results may be confounded by behaviours that were unable to be accounted for and that the duration of the protection and effectiveness against severe disease are uncertain.

Another preprint study from the United States, contracted by the vaccine manufacturer Moderna, reports a vaccine effectiveness of 30.4% (95% CI: 5.0%, 49.0%) against Omicron infection after two doses of the Spikevax vaccine. A third (booster) dose increased the effectiveness to 62.5% (95% CI: 56.2%, 67.9%). The study also reports considerably lower vaccine effectiveness against Omicron infection among immunocompromised individuals compared to the general population.  

Earlier studies from the UK and Denmark showed significantly reduced and declining vaccine effectiveness against symptomatic disease with Omicron compared to infection with Delta. These studies also reported that a booster dose increased the vaccine effectiveness, although not as efficiently as against infection with Delta. The additional protection from booster doses against infection with Omicron was also confirmed in a recent study from Scotland.

Estimates of vaccine effectiveness against hospitalisation from the UK and South Africa have indicated that the protection against severe disease from Omicron infection is higher (around 70% after primary vaccination) than the protection against mild infections, and that the protection increases after a third vaccine dose.

The estimates of vaccine effectiveness against Omicron should still be considered as preliminary evidence, and more data are awaited from larger populations that allow for stratification of data by age, vaccine type, number of doses received, and time since vaccination. Studies and collection of real-life data are ongoing to further assess the level of protection from the vaccines against transmission, infection, and severe disease.

Overall level of risk and options for response

Based on the current situation and the available evidence, ECDC’s Rapid Risk Assessment (18th update) on the impact of Omicron remains valid: the overall level of risk to public health associated with the further emergence and spread of the SARS-CoV-2 Omicron VOC in the EU/EEA is assessed as VERY HIGH.

The very high growth advantage of Omicron has resulted in very high case notification rates. Such high levels of SARS-CoV-2 transmission leads to high levels of absence from work, including among healthcare and other essential workers, and likely overwhelm the testing and contact tracing capacities in many EU Member States. The sheer volume of COVID-19 cases places considerable strain on healthcare systems and society. ECDC has provided options for adapting quarantine and isolation, particularly when countries face high or extreme pressure on healthcare systems and other functions in society, including essential services.

Please see the ECDC’s Rapid Risk Assessment for epidemiological forecasts and options for response (non-pharmaceutical interventions, health system strengthening, vaccination, testing and contact tracing, and risk communication). ECDC will publish updates on the epidemiological situation, severity, spread, and vaccine effectiveness in short intervals.

Awaiting the availability of further evidence, urgent and strong action is needed to reduce transmission, keep the burden on healthcare systems manageable, and protect the most vulnerable.

Member States should urgently assess their acceptable levels of residual risks, current healthcare system capacities, and available risk management options (e.g.  contingency and business continuity measures, surveillance and testing strategy, quarantine and isolation policy, etc.).

The continuation and strengthening of non-pharmaceutical interventions is necessary to reduce ongoing Delta and Omicron transmission and keep the COVID-19-related disease burden manageable. These measures include avoiding large public or private gatherings, extended use of face masks, reduced contacts between groups of individuals in social or work settings, teleworking, and reduced inter-household mixing.

Vaccination remains a key component of the multi-layered approach needed to address the ongoing circulation and reduce the impact of the Delta and Omicron variants. Efforts should continue to increase full vaccination uptake in individuals who are currently unvaccinated or partially vaccinated and accelerate the roll-out of booster doses.

Member States are strongly encouraged to conduct and share findings on outbreak investigations and epidemiological studies to inform future risk assessments.