The Omicron BA.4 and BA.5 variants were reported for the first time in South Africa in January and February this year, respectively. As subtype variants of Omicron, the BA.4 and BA.5 strains share a common origin with earlier Omicron strains. But as a variant, it has the property of spreading infection more easily and evading the immune system.
Although BA.4 and BA.5 are less likely to cause severe disease than other Omicron subtypes. But its higher transmission rate has the potential to lead to large-scale contagion that can lead to surges in hospitalizations and deaths.
Since 2022, many countries have successively lifted epidemic restrictions on corresponding prevention and control measures, which also provided a realistic background for the rapid spread of Omicron BA.4 and BA.5 variants. Some countries have faced a severe epidemic situation: the number of infected people has increased exponentially, the medical system has been challenged, and patients who have recovered from the COVID-19 are re-infected...
PART 01
What are the Omicron BA.4 and BA.5 variants?
First of all, Omicron is the code name of the B.1.1.529 variant of COVID-19. In November 2021, South Africa reported the B.1.1.529 variant to the WHO. The WHO gave this variant a name called Omicron 24 hours later.
The Omicron has five branches, called BA.1, BA.2, BA.3, BA.4, and BA.5. Among them, BA.3 lineage spreads at very low speeds and cause fewer cases. The BA.4 and BA.5 lineage belong to two subtypes of the Omicron clade and share the same spike protein. Compared to BA.1, which causes widespread infection in most countries late last year, BA.4 and BA.5 are very similar to BA.2, but differ in the presence of several additional mutations such as the Δ69-70 deletion and L452R and the F486V mutation.
According to Nature, the most important change brought about by these mutations (mainly L452R, F486V) is that BA.4 and BA.5 are increasingly able to evade the body's existing immune system. These mutations could alter its ability to lock onto host cells and evade certain immune responses, allowing reinfection in people who have been vaccinated or have been infected with COVID-19.
PART 02
Why are the Omicron BA.4 and BA.5 variants more transmissible?
BA.4 and BA.5 were first detected in South Africa in January 2022 and quickly became the predominant circulating strains. Then, both subtypes were also found in a dozen other countries, mostly in Europe. Portugal was the first country in Europe to report one of these two subtypes (BA.5). BA.5 became the main circulating strain in Portugal in May. Apart from Portugal, in many EU countries, like Austria, Belgium, Denmark, France, Germany, Ireland, Italy, Netherlands, Spain and Sweden, there are statistics showing an increase in the proportion of BA.4 and BA.5 infections.
The transmission advantage of mutation may come from biological changes that accelerate infection. But Christian Althaus, a computational epidemiologist at the University of Bern, said that the rise in infection rates in BA.4 and BA.5 appeared to be caused by their ability to infect early forms of Omicron and other mutant-immune people. As most parts of the world outside Asia have little control over COVID-19, the rise in BA.4 and BA.5 will be driven almost entirely by population immunity. Cases increase when population immunity is low, and only drop when enough people are infected.
Based on the rise in BA.5 in Switzerland (where the prevalence of BA.4 is lower), Althaus estimates that around 15% of people there will be infected in this wave. But Althaus added that the current immunization status of countries and regions may vary due to their different COVID-19 wave histories and vaccination rates. Therefore, the size of the BA.4 and BA.5 waves will vary from place to place. "It could be 5% in some countries, 30% in others. It all depends on their immunization status," he said.
According to the study published in Cell on June 8, BA.4 and BA.5 did have a more significant escape from the sera of 3-dose vaccine recipients, with great potential to cause a new wave of infection. Compared to BA.1 and BA.2, BA.4 and BA.5 are more resistant to neutralization by three doses of vaccinated sera.
PART 03
What is the impact of Omicron BA.4 and BA.5 variants on COVID-19?
The BA.4 and BA.5 subtypes sparked a global infection surge because they spread faster than other prevalent variants (mainly BA.2), which also led to a surge in cases earlier this year. But so far, the latest Omicron variants appear to have caused fewer deaths and fewer hospitalizations than their predecessors. This is a good indication that the continuous improvement of population immunity has greatly mitigated the consequences of the collapse of the medical system and social environment that may be brought about by the surge of COVID-19 cases.
"It can also vary from country to country," said Waasila Jassat, a public health expert at the National Institute of Infectious Diseases in Johannesburg, South Africa. "Despite the high number of infections, hospitalizations and deaths in South Africa during the BA.4 and BA.5 surges has only increased slightly"
In a study to be published on the medRxiv preprint server, Jassat and her colleagues found that South Africa had similar hospitalization rates during waves of BA.4 and BA.5 compared with earlier waves of Omicron infections. But the death rate was slightly lower. In terms of hospitalizations and deaths, both Omicron's waves of infections were much milder than that of Delta.
In countries other than South Africa, the impact of BA.4 and BA.5 are more pronounced. In Portugal, although COVID-19 vaccination and booster vaccination rates are already very high, the latest wave of infections has resulted in levels of mortality and hospitalization similar to the first wave of Omicron infections (Which although compared to earlier waves is much better).
"One reason for this difference could be Portugal's demographics," Althaus said. "The older you are, the more severe the disease." And Jassat believes that a country's immunity could also explain the different results. About half of South African adults are vaccinated, but only 5% receive a booster shot. But combined with the extremely high infection rates of previous waves of COVID-19, people have built a wall of "mixed immunity" that provides strong protection against severe disease, especially for those elderly who are most in need of vaccination.
Due to the general improvement of Europe's overall immunity to COVID-19 and the relatively weakened virulence of the Omicron variant, the number of hospitalizations in this wave of epidemics has been relatively stable. But German experts have warned that in the worst case, hospitals still may be overwhelmed.
The German Medical Association (BÄK) recently urged the government to prepare for an epidemic rebound in fall and winter, and called on the government to develop additional plans to keep schools open, protect vulnerable groups and avoid medical crash.
PART 04
Hecin Reagents Effectively Detect Omicron BA.4 and BA.5 Variants
Since 2020, Hecin's 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) have continued to provide strong support globally to fight against the pandemic. Hecin pays close attention to the mutant strains of COVID-19 appearing around the world, attaches great importance to the impact of genetic mutations on the nucleic acid detection of the 2019-nCoV, and continues to track, evaluate and verify the emerging genetic mutations of COVID-19.
For COVID-19 mutant strains reported by the World Health Organization, Hecin has evaluated and verified the detection effect of 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) and 2019-nCoV Antigen Test Kit (colloidal gold method) for the main mutant strains of COVID-19, including bioinformatics, the comparison of all simulated samples and the detection and verification of some real samples. Our 2019-nCoV Nucleic Acid Test Kit (PCR- fluorescence probe method) and 2019-nCoV Antigen Test Kit(colloidal gold method) can effectively detect the latest Omicron BA.4 and BA.5 variants by bioinformatics analysis.
Currently, Hecin's 2019-nCov nucleic acid detection solution has served many countries and regions around the world and can accurately detect popular variants such as Alpha, Beta, Gamma, Delta, Lambda, and Omicron. Hecin will continue to closely track the latest developments of the COVID-19 variants globally, always ensure the specificity, accuracy and sensitivity of the products, and continue to help the prevention and control of COVID-19.
