The impact of an omicron outbreak at a private gathering in the Faroe Islands

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 classified it as a variant of concern (VOC) two days later. The nail protein, which is the major antigenic target for antibodies generated by infection or immunization, has 26 to 32 mutations in the Omicron variation.

Early reports suggest that Omicron has higher transferability and immunological escape potential than previous variants, while a neutralization study showed that previously infected and vaccinated mice with the Omicron variant had reduced neutralizing activity.

Study: Omicron outbreak at a private gathering in the Faroe Islands that infected 21 out of 33 triple-vaccinated health workers.  Image credit: haidaralf / ShutterstockStudy: Omicron outbreak at a private gathering in the Faroe Islands that infected 21 out of 33 triple-vaccinated health 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 rapidly within and outside Europe during the first weeks of December 2021. Due to the rapid spread, it is expected that the Omicron variant will become the dominant form in a short time, so monitoring the severity and transferability of the Omicron variant will be crucial in the coming weeks and months.

Although all infected participants had been vaccinated three times and had a recent negative test, this article from a team of researchers from the Faroe Islands describes a super-spreading event in which 21 out of 33 healthcare professionals became infected with the Omicron variant after participating in a social togetherness in early December 2021.

A pre-printed version of this study, which has yet to undergo peer review, is available at 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 turned out to be positive. Thereafter, the remaining individuals performed PCR tests, with 21 out of 33 participants testing positive, resulting in an attack rate of 63.6%. The extremely high attack rate prompted the Faroese chief physician to request virus genome sequencing, which resulted in the discovery of the first Omicron variant on 8 December. Through targeted sequencing, 13 samples from the collection 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 possible 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 no one had previously been infected with SARS-CoV-2. Within 36 hours of collection, 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 the affected people. Muscle and joint discomfort, fatigue and fever were the most common symptoms, whereas loss of taste and smell were the least common. There were no admissions.

The incubation period was short and ranged from 2 to 6 days with an average incubation period of 3.24 days if the SARS-CoV-2 exposure took place on the evening of the collection. The time it took for symptoms to disappear varied, and five people still had symptoms at the end of the study, while the rest had symptoms for 1 to 9 days.

Implications

These results suggest that the Omicron variant has potent immune-escape abilities, putting even newly boosted patients at risk of infection. In this study, Omicron had a short incubation period. If the incubation period for Omicron is shorter than for previous versions, this may explain why the infection rate is higher in humans with some immunity. This short study does not allow for estimation of hospitalization or death rates. The chance of developing Long Covid following an Omicron infection is unknown at this time. Despite the fact that the subjects in this study mostly had moderate illness, all the reported cases had previously gained immunity by vaccination.

It is worth noting that all infected people had symptoms and that loss of taste and smell, in particular, seems to be less common in these cases than in previous outbreaks. Although protection against infection has faded, vaccination is likely to still protect against serious illness with the Omicron variant, underscoring the value of vaccination. It is worth noting that the results may not apply to SARS-CoV-2 naive people, and therefore more research is needed in Omicron with SARS-CoV-2 naive people.

*Important message

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

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