On November 24, researchers in South Africa became the first to report the B.1.1.529 variant of the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2).

The World Health Organization (WHO) designated the variant Omicron and classed it as a variant of concern (VOC) two days later. The spike protein, which is the principal antigenic target of antibodies generated by infection or immunization, has 26 to 32 mutations in the Omicron variation.

Early reports imply that Omicron has higher transmissibility and immunological escape potential than earlier variants, while a neutralization investigation found that previously infected and vaccinated mice with the Omicron variant had decreased neutralization activity.

Study: Omicron outbreak at a private gathering in the Faroe Islands, infecting 21 of 33 triple-vaccinated healthcare workers. Image Credit: haidaralf/Shutterstock

Despite the fact that several nations around the world have implemented travel restrictions to prevent the Omicron variant from spreading, the variant managed to spread swiftly inside Europe and beyond during the early weeks of December 2021. Because of the rapid spread, it is expected that the Omicron variant will become the dominant form in a short period of time, so monitoring the severity and transmissibility of the Omicron variant will be crucial in the coming weeks and months.

Even though all infected participants had been vaccinated three times and had a recent negative test, this paper from a team of researchers from the Faroe Islands describes a super-spreading incident in which 21 of 33 healthcare workers were infected with the Omicron variant after attending a social gathering in early December 2021.

A preprint version of this study, which is yet to undergo peer review, is available on the medRxiv* server.

The study

A private gathering of 33 people took place in early December 2021. Several people began to experience symptoms over the next few days and took a PCR test, which came out positive. Following that, the remaining individuals did PCR tests, with 21 of 33 participants testing positive, resulting in a 63.6% attack rate. The extremely high attack rate prompted the Faroese Chief Medical Officer to request virus genome sequencing, which resulted in the discovery of the first Omicron variant on December 8. Through targeted sequencing, 13 samples from the gathering and 4 more from the extended transmission chain have been confirmed as the Omicron variant. The Omicron variant is also suspected in the remaining cases. It has not been feasible to pinpoint the index case that started this transmission chain, but the variant was most likely imported from another country.

All affected subjects had received a third booster dose of the mRNA vaccine BNT162b2 (Comirnaty; BioNTech, Mainz, Germany) within the last two and a half months, and none had previously been infected with SARS-CoV-2. Within 36 hours of the gathering, all affected persons had a negative test. The majority had done a PCR test, and five had done a lateral flow test. Symptoms appeared in all of the afflicted people. Muscle and joint discomfort, weariness, and fever were the most prevalent symptoms, whereas loss of taste and smell were the least common. There were no hospitalizations.

The incubation period was short, spanning from 2 to 6 days, with a mean incubation period of 3.24 days if the SARS-CoV-2 exposure occurred on the evening of the gathering. The time it took for symptoms to go away varied, and five people still had symptoms at the end of the study, while the remainder had symptoms for 1 to 9 days.

Implications

These findings suggest that the Omicron variant has potent immune-escape capabilities, putting even newly boosted patients at risk of infection. In this investigation, Omicron had a short incubation period. If the incubation period for Omicron is shorter than for prior versions, this could explain why infection rates are higher in people who have some immunity. This short study does not allow for the estimation of hospitalization or death rates. The chance of developing Long Covid after an Omicron infection is unknown at this time. Despite the fact that the individuals in this study mostly had moderate sickness, all of the reported cases had previously acquired immunity by vaccination.

It's worth noting that all infected people had symptoms, and that loss of taste and smell, in particular, appears to be less common in these instances than in prior outbreaks. Even if protection against infection has faded, vaccination is still likely to protect against severe disease with the Omicron variant, underscoring the value of vaccination. It's worth noting that the findings might not apply to SARS-CoV-2 naive people, thus more research in Omicron with SARS-CoV-2 naive people is needed.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Colin Lightfoot

Colin graduated from the University of Chester with a B.Sc. in Biomedical Science in 2020. Since completing his undergraduate degree, he worked for NHS England as an Associate Practitioner, responsible for testing inpatients for COVID-19 on admission.