"It could be a more potent virus than BA.1, more contagious and causing more severe disease."
Written by | Lingjun
Source | "Medical Community" public account
At present, European and American countries have successively liberalized epidemic prevention measures, based on one of the reasons for the decline in the toxicity of Omicron.
But a new study in Japan found that BA.2, a new sub-variant known as an upgraded version of Omicron, may not be as toxic as everyone thinks.
On February 15, Japanese researchers published a study in the preprint bioRxiv, saying that BA.2 may be able to cause serious diseases like older variants of the new coronavirus, including Delta, but will also spread further around the world. The article even proposes that BA.2 should be given a new Greek letter to distinguish it from Omicron BA.1.
This result has attracted everyone's attention: since February this year, the number of BA.2 infections worldwide has been rising, and it has also entered China. According to the Shenzhen Health Commission, several transmission chains/points of the epidemic in Shenzhen in recent days, the source of infection virus is Omicron BA.2.
BA.2 may lead to more severe illness
Previously, the academic community agreed that the spread of BA.2 was about 1.4 times that of BA.1, but there was no evidence to clarify the difference in toxicity between the two.
This time, Japanese researchers specially conducted hamster infection experiments for comparison.
The researchers found that after infection, the RNA load of peripheral BA.2 in hamster lungs was significantly higher than THAT of BA.1, which was 9.3 times. Over time, the expression of BA.2 viral RNA can continue to be detected in lung tissue, while ba.1 is much lower and gradually disappears.
At the same time, BA.1-infected hamsters showed no or only mild symptoms of the disease. Ba.2 was different, and the infected hamsters all showed symptoms of weight loss and respiratory disease.
The researchers said BA.2 spreads faster and more efficiently in lung tissue than BA.1. According to all histopathological parameters of BA.2 infected hamsters, the levels of bronchitis, bleeding, and alveolar injury were significantly higher than those of BA.1 infection.
This suggests that BA.2 may be more pathogenic than BA.1. "It may be a more potent virus than BA.1, and it is more transmissible and causes more serious disease." Dr. Daniel Rhoads, head of the microbiology unit at the Cleveland Clinic in Ohio, said.
"Herd immunity" after infection,
Probably not that effective
The number of acquired immunization after infection is relatively large, which is one of the "hard shoulders" of European and American countries.
As the dominant strain of the global pandemic, can people it infected avoid being attacked by BA.2? Japanese researchers analyzed serum from 17 people who had recovered from BA.1 virus and found:
BA.1 convalescent serum showed strong antiviral effects on BA.1 strains, but appeared to be less effective in BA.2, with 1.4 times more resistant serum than BA.1. The researchers conducted experiments again in mice and came to similar conclusions:
Compared with BA.1, BA.2's resistance to ba.1 convalescent hamster serum increased significantly by about 2.9-fold.
The researchers also obtained antiserum from BA.1's S protein cell immune mice, using a murine serum neutralization assay, and the results showed that BA.2 was 6.4 times more resistant to immune serum than BA.1.
Not to mention patients who were infected early in the pandemic.
Studies have shown that ba.2, like BA.1, is highly resistant to convalescent serum, whether it is the original strain, Alpha, or Delta.
The simple understanding is that whether you were infected with other variants early on or recently infected with BA.1, when facing BA.2 again, it may not be as "safe" as you think.
Is the vaccine still useful? What about antiviral drugs? In this respect, BA.2 continues the capabilities of BA.1 and seems to be slightly superior.
Experiments with pseudoviruses and vaccination-induced neutralizing antibodies have shown that BA.2 is highly resistant to both mRNA and adenovirus vaccines. In addition, BA.2 is almost completely resistant to two therapeutic monoclonal antibodies, Casirivimab and Imdevimab.
British scholars question the government:
Relaxation of epidemic prevention should provide scientific basis
However, mouse experiments do not fully reflect the actual situation, and there are certain differences between the pathology and infection dynamics of viruses between humans and laboratory animals.
Back in the real world, the evidence for the severity of BA.2 is mixed. In countries where the outbreak has been suspended, such as South Africa and the United Kingdom, hospitalizations continue to decline. But in Denmark, WHERE BA.2 has become a major source of infection, with hospitalizations and deaths on the rise.
This study is more like a wake-up call for us. Deborah Fuller, a virologist at the University of Washington School of Medicine, believes that establishing a system dedicated to testing for BA.2 will be the first thing many countries need to do.
Distinguishing between BA.1 and BA.2 requires whole genome sequencing, which is a relatively time-consuming and labor-intensive process, and in countries where the number of cases is increasing by tens of thousands, it is not easy to obtain relevant data and analyze it in a timely manner.
"Is humanity outperforming the virus at the moment?" Until the relevant data comes out, I don't think the epidemic prevention regulations can be lifted. Professor Deborah Fuller said.
Penelope Toff, president of the Public Health Medical Branch of the British Medical Association, said a few days ago that the number of confirmed cases is still very high, with hundreds of deaths every day, but the United Kingdom has canceled self-isolation and other epidemic prevention measures. "We have the right to question whether there is a scientific basis behind the government's decision."
Lawrence Young, a virologist at the University of Warwick, believes that the pandemic is not over.
"If there's anything we've learned over the past two years, it's that the impact and future of COVID-19 remains unpredictable." Lawrence Young said.
References;
[1] Covid-19:Show us evidence for lifting restrictions,doctors tell Johnson，https://www.bmj.com/content/376/bmj.o383
Source: Medical community
Editor-in-charge: Ling Jun
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