The sub-variant is 30% more contagious with a shorter incubation time. What do we know about symptoms, contagiousness, vaccine protection and the possibility of reinfection
In Europe, the coronavirus has started to run again: infections are increasing everywhere. Just as countries are training the restrictions, including Italy, once again Covid raises its head pushed by the increase in the circulation of subvariante Omicron BA2which it seems more transmissible of the high variants Covid -19 said at the press conference Marco Cavaleri, head of the EMA vaccination strategy. According to US immunologist Anthony Fauci BA.2 is assuming a greater degree of dominance globally and now reaches 60%.
We do not know how widespread the variant is in Italy. The last monitoring of the Istituto Superiore di Sanit dates back to January 31 and at the time BA.2 represented the 3% of the sequences. Some information emerges from independent investigations of various laboratories. For example, we know that Omicron represents 58% of positive cases in the Bergamo area. In Umbria Omicron 2 was identified in 60% of 56 swabs sequenced on 7 March last.
How contagious is the virus now?
All Omicron subvariants are highly contagious, which is why the Omicron variant quickly eliminated Delta, already more contagious than Alpha. Numerous studies have found that the sub-variant BA.2 even more transmissible than BA.1. In Denmark, scientists looked at the prevalence of both subvariants in families and found that people infected with BA.2 were substantially more likely to infect people they shared a home with than those with BA.1.
The studies conducted so far hypothesize one contagiousness greater than 30% compared to the Micron. The data have yet to be confirmed but if this were the case we would be faced with the most contagious virus ever to appear on the planet, with an R0 between 15 and 18: in the absence of countermeasures an infected person could infect another 15-18, more than measles .
What is the incubation time?
In England, researchers found that on average a person with BA.2 took less time to infect another person, accelerating its diffusion in communities with shorter incubation times.
The average time of onset of symptoms would appear to be approx half a day shorter for BA.2 compared to BA.1, with an average period of 3.27 days versus 3.72 days respectively.
With Delta, the interval between infection and the onset of symptoms was approximately 4 days. The shorter incubation time could contribute to the increase in the growth rate of BA.2
How much does the vaccine protect against disease?
The vaccine continues to be protective against hospitalization and serious illnessalso against Omicron 2.
Indeed, the data in the latest report by the UK Health Security Agency relating to the effectiveness of vaccines in preventing the symptoms of Covid disease show that up to the ninth week the vaccines even guarantee a higher protection against BA.2. A study of 21 hospitals in the United States confirms 86% protection against hospitalization with three doses of the vaccine.
How much does the vaccine protect against infection? What are the symptoms?
However, numerous studies underline a decline in vaccine protection againstinfection that varies between 44% and 72%, even with three doses.
And for this reason that many people, despite having done the booster, are now becoming infected, presumably with BA.2particularly if the injection occurred months ago.
In the vast majority of cases i vaccinated people who are infected have mild symptoms such as a headache, sore throat or coldWithout vaccination, we would have double the number of cases: vaccination hinders the spread of the virus, commented the virologist of the San Raffaele hospital in Milan. Roberto Burioni.
possible to recontact?
With BA.2, as it was already with Omicron, reinfections are possible. For example, a person who became infected a year ago with Delta or two years ago with Alpha could recover Omicron or Omicron 2 because the new variants have important mutations compared to the previous viruses and the organism did not produce specific antibodies. In Lombardy 5/6 percent of reinfections emerge every day (most people, about 4 percent, were not protected with the anti-Covid vaccine after the first infection). Even the Istituto Superiore di Sanit reports a 3.3% reinfection rate and most at risk are young people, women and health professionals.
The good news that those infected with Omicron should instead be highly protected by BA2: the new sub-variant would not be able to circumvent the immunity acquired with Omicron, at least in the short term.
However, a Danish study identified 47 cases of BA.2 infections that occurred shortly after a BA.1 infection: mostly young people who were mostly unvaccinated. Omicron BA.2 reinfections can occur shortly after BA.1 infections, according to the report authors. but they are rare. However, the World Health Organization has stated that infection with Omicron provides strong protection against BA.2 infection.
The most serious disease?
There is currently limited evidence on possible differences in BA.1 and BA.2-induced disease severity. An analysis conducted in Denmark
showed no difference in the risk of hospitalization between people infected with BA.1 or BA.2. British researchers also found that BA.2 infection does not carry a higher risk of hospitalization than BA.1. So far, only Japanese researchers who have infected hamsters with the two variants have found that BA.2 causes a more severe disease.
What are the symptoms?
The symptoms caused by Omicron 2 seem no different than Omicron. Both strains cause milder symptoms than Delta, in particular affecting the upper respiratory tract and the disease manifests itself in most cases as a cold or mild flu with muscle and joint painat least among those vaccinated.
Anecdotal reports point to the spread of intestinal symptoms such as nausea, diarrhea, vomiting, abdominal pain, heartburn and bloating. However, these are self-reports collected by the scholar Tim Spector through the Covid Symptom Study app. Official reports report no symptoms other than Omicron.
Do drugs work?
Like BA.1, BA.2 also capable of evade most treatments with monoclonal antibodiesmaking them ineffective. The preventive monoclonal Evusheld of AstraZeneca, however, retains the ability to neutralize the sub-variant Omicron BA2. Other monoclonals that did not work against BA.1 instead demonstrated neutralizing activity against BA.2 according to a very recent study published in the New England Journal of Medicine. Antiviral drugs Paxlovid, molnupiravir and remdesivir all remain highly effective against both variants of Omicron if taken quickly, immediately after a positive test but to understand its real effectiveness, specific clinical studies on BA are needed.
March 17, 2022 (change March 17, 2022 | 17:30)
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