Is the Omiljung BA.2 variant really more contagious and destructive than the true One?

True points:

BA.2 mutants have been found in more than 40 countries around the world, and the proportion of BA.2 is also rising in the sequencing of all genomes, showing that BA.2 has the potential to become a mainstream mutant strain in different countries and regions. In terms of propagation speed, BA.2 is indeed faster than BA.1. However, whether BA.2 is more pathogenic, according to the real-world tracking, there is no significant difference between the two.

Verifier: Ph.D. in Genetics, Popular Science Author, Practitioner of New Drug Research and Development

At a time when the number of new cases of Omicron began to decline globally, another mutant strain began to attract attention – BA.2, a branch of Omicron. There have also been recent reports that BA.2 spreads faster or can lead to more severe conditions. So, what kind of impact will BA.2 have on the epidemic?

First, there is potential to dominate the mainstream

BA.2 is now very concerned because it has been found in more than 40 countries around the world, which can be said to have international influence. In addition, the proportion of BA.2 is rising in the sequencing of all genomes, which means that it appears to have a competitive advantage over other mutant strains, leaning in the direction of the mainstream mutant strains.

As of February 14, BA.2 accounted for the majority of new cases (>50%) of the sequences submitted to the COVID-19 genome sequencing information base GISAIDs in 10 countries, including several Asian countries such as China, India, and the Philippines. Now the epidemic in Hong Kong is mainly BA.2.

The whole genome sequence of viruses submitted to the COVID-19 Genome Sequence Bank is affected by the sequencing capacity and sampling quantity of different countries, and may not accurately reflect the actual prevalence ratio of mutant strains. If you look at the different countries' own tracking separately, in South Africa, the proportion of BA.2 increased from 27% on February 4 to 86% on February 11. Denmark rose from 20% at the end of 2021 to 45% in early January 2022.

It should be noted that among the countries where the proportion of BA.2 has increased, there are both countries where the peak of Omicron has passed and the overall number of cases has declined, as well as areas where the Omicron outbreak has just occurred, showing that this subsponsm has the potential to become a mainstream mutant strain in different countries and regions.

Second, the spread speed is faster

The mainstream mutant strain in the world today is Omicron's BA.1, so the characteristics of BA.2 discussed now are generally compared to BA.1. A very clear feature now is that BA.2 spreads faster than BA.1, which is why the proportion of BA.2 in many countries is rising, and even dominates.

For example, Denmark compared the growth rate of BA.1 and BA.2 in the local area and found that the spread capacity of BA.2 increased by 30% compared with BA.1. The United Kingdom and Denmark have also done a secondary attack rate of BA.2 and BA.1 in families, and both found that ba.2 has a higher risk of further transmission in the family, such as the British study showed that the second-generation incidence of BA.2 in the family was 13.4%, while BA.1 was 10.3%.

Why does BA.2 spread faster than BA.1? Further research is still needed in this area. In terms of specific mutations, THERE are many differences between BA.2 and BA.1 (see figure below):

Figure: Schematic diagram of the coincidence of mutation sites of various variant strains of Omikeron

Humans can produce an immune response to both mutant strains, and a Danish comparison of the transmission of the two mutant strains in the home found that BA.2 also spreads faster than BA.1 in unvaccinated people, and these preliminary studies point to BA.2 as having a stronger ability to spread than BA.1, rather than more severe immune escape.

Third, the pathogenicity is not necessarily more serious

Does BA.2, which spreads faster than BA.1, cause more serious conditions? A recent Japanese study has attracted a lot of attention, showing that hamsters infected with BA.2 are more disease-intensive than BA.1, that is, BA.2 may be more pathogenic than BA.1.

The study caused some people to panic, but this is only a preliminary study, in the real world, from the United Kingdom, Denmark and South Africa tracking, BA.2 and BA.1 show no difference in pathogenicity. For example, in a study in South Africa, researchers analyzed 95,000 cases of COVID-19-positive infections and found that 3.6% of people with BA.2 infection required hospitalization, compared with 3.4% in BA.1, with no significant difference.

However, it should be noted that the United Kingdom, South Africa and Denmark are all countries with a relatively high COVID-19 immunization base, the Vaccination Rates of the United Kingdom and Denmark are very high, and South Africa has a lot of natural infections in the past, and the population structure is also younger, so the results observed in these countries should also be carefully interpreted. For example, now that Hong Kong BA.2 has caused a large-scale epidemic, and the vaccination rate among the local elderly is low, it is necessary to be vigilant about whether there will be more serious diseases.

Fourth, the impact on the epidemic may be limited

Most importantly, from the current data, the impact of BA.2 on the overall global epidemic may be limited. Although the proportion of BA.2 in the global new cases has increased recently, the overall number of COVID-19 infections is still declining. This suggests that BA.2 may not trigger a new wave of global outbreaks.

Why did Omicron cause such a big outbreak when BA.1 was dominant, while BA.2 spread faster but was unlikely to trigger a new wave?

This is because BA.2 is relatively similar to BA.1 in terms of immune escape. From serum neutralization experiments, the ability of three mRNA vaccinators to neutralize two subspons in the serum is similar. The UK study also found that the effectiveness of BA.2 and BA.1 was similar after vaccination (BA.1 was 63% effective and BA.2 was 70%) after vaccination.

Moreover, the natural immunity formed by infection with BA.1 also has a protective effect on BA.2. A Danish study examined the sequencing results of 140,000 viruses after Omicron was dominant, analyzing whether there were secondary infections. Only 263 cases of secondary infection were found within 1-2 months of infection. Of these, 190 were secondary infections caused by BA.2, but only 47 cases were infected with BA.1 and then BA.2, and the rest were infected with Delta first. Young people who are not vaccinated in the secondary infection are less severe. This shows that although BA.2 can break through the natural immunity brought about by past Omicron BA.1 infection, breakthrough infection is relatively rare and predominantly mild.

Vaccination rates are now relatively high in many parts of the world, and there have been a large number of cases of BA.1 infection in the recent past. In this case, the population immunity barrier that BA.2 has to face is very high, so it is difficult to trigger a new wave of outbreaks around the world.

However, due to the more contagious nature, the emergence of BA.2 may slow down the decline rate of Omicron's epidemic cases globally, forming a long-tail effect. Moreover, studies have shown that some monoclonal antibody drugs that are effective against BA.1 may experience a decrease in effectiveness against BA.2. All of this requires us to remain vigilant about BA.2.

This article was edited by: courtneyli

Pay attention to [more true] to get more reliable knowledge.

Copyright Notice: This article is a true copyright manuscript of Tencent, unauthorized reproduction is prohibited. Individuals are welcome to forward to the circle of friends.