Question asked by Nicolas on December 30
Researchers in the Faroe Islands, Denmark uploaded on December 23 an article in prepublication, reporting “A super-spread event of omicron infections among triple-vaccinated healthcare workers” who all had “Participated in a private meeting”.
According to this report, these caregivers gathered over an evening “At the beginning of the month of December”. In the following days, several of them developed symptoms suggestive of Covid. All of the 33 people initially gathered performed a PCR test, which turned out to be positive for 21 of them. A proportion “Unusually high”, which led those in charge of the case to request the sequencing of the virus.
The authors of the study specify that this sequencing, which began on December 8, led to the first identification of omicron in the Faroe Islands. At the time of presentation of these results, 13 of the 21 initial samples, as well as four others from contact cases, had been confirmed positive for the variant. Solicited by CheckNews, the authors tell us that all the participants in the evening, and not just the 21 infected, “Had carried out a test – negative in all cases – in the thirty-six hours preceding the assembly”.
Notable fact: all of the infected presented symptoms. “The most common were fatigue (15 cases), fever (13 cases), muscle pain (13 cases) and joint pain (11 cases), the least common being loss of taste (5 cases) and smell. (4 cases) “, detail the researchers. In most patients, symptoms resolved between one and nine days after onset – only five people still reported symptoms two weeks after infection. No situation required admission to hospital.
Several unknowns remain on this file. Could all the participants working in the same sector of activity have been infected elsewhere than during the famous private meeting? For example, at their workplace, over several days? A question all the more legitimate since, according to the article, the person at the origin of the contamination has not been identified. Asked by CheckNews on this possibility, the authors of the study judge this possibility “Possible, although unlikely” in view of the circumstances favorable to contamination during the evening (prolonged proximity, absence of wearing a mask).
The dates of onset of symptoms are well compatible with this hypothesis. “If we assume that the exposure to Sars-CoV-2 took place on the evening of the gathering,” write the researchers, “The incubation period was short, ranging from two to six days”, with an average incubation period of just over three days. In fact, several recent publications point to a much lower incubation time for omicron than for the previous variants, of the order of three days.
The 21 infected were all fully vaccinated, with three doses of Pfizer’s Comirnaty. The authors tell us that except for one participant vaccinated on December 2 (a few days before the famous meeting), all had received a booster dose. “At least three weeks ago”. If in the first case, the time is clearly insufficient for the booster to be considered effective, the same does not apply to the rest of the guests. However, the authors could not tell us whether a significant proportion of the uninfected participants had received a third dose longer than the infected ones.
Finally, it should be noted that no investigation into the quality of the vaccine batch (s) administered to the members of the cluster has apparently been carried out.
Numerous studies carried out for a little over a month have confirmed that the omicron variant is capable of bypassing part of the immune defenses of people immunized against other variants (the virus carries around thirty mutations in the spike protein, the main antigenic target. antibodies generated by infection or vaccination).
Recent Danish work, relating to the first 785 cases of omicron in the country, also shows that 76% of cases concern double vaccinated people (i.e. half more than what is observed for delta), and 7% of triple vaccinated. (ie double what is observed for delta). A recent Norwegian study on a cluster of people who were essentially double vaccinated (96%) also confirmed the significant dispersal capacity of the variant during an evening in a restaurant: three quarters of the guests had been infected by omicron.
The Faroese study illustrates, at a minimum, the fact that people recently vaccinated with a booster dose still run the risk of being infected. The researchers note, however, that the available data still suggests “That vaccination also protects against serious forms of the disease”, even with the omicron variant, “Which further underlines the importance of vaccination.”
The authors of the article consider that this case “Shows the importance of social distancing and avoiding large festive gatherings during the pandemic to prevent possible super spread events”. They specify that the chain of transmission which involves study participants “Apparently stopped after about 70 cases,” “demonstrating that with effective contact tracing, an omicron transmission chain can be contained.”
End December, four-fifths of the Faroese population had a full vaccination schedule (two doses or one dose post-infection), and a quarter had received a booster dose.