43% of new cases worldwide caused by Omicron variant strain BA.5 Virus

BA.5 was first detected in South Africa in February this year, and according to the World Health Organization (who) report on June 22, ba.5 has spread to 62 countries around the world.

According to the WHO report on June 29, in the 24th epidemiological week (June 13-19), ba.5 accounted for 43% of new cases, exceeding ba.2 (25%), becoming the mainstream strain of the new round of global epidemics.

The spread of ba.5 has also led to the rebound of the global epidemic that has just escaped from the "claw" of ba.2.

According to who's report, affected by ba.5/ba.4, from June 20 to June 26, the number of new cases worldwide reached 4.1 million, a growth rate similar to that of the previous week (June 13-19). ) increased by 18%, the highest value since April.

Among them, the situation in the Eastern Mediterranean, Europe, Southeast Asia and the Americas is more serious.

In the Americas, the United States and Canada are all heavily influenced by ba.5.

The number of confirmed cases in Canada has shown an upward trend again in recent days, with an average of about 2,300 new confirmed cases per day, compared with the previous low of 1,561.

According to the prediction of Prof. Sarah Otto, an expert in modeling the rapid response network for coronavirus variants in Canada, ba.5 will account for 70% of the new cases in early July. Affected by this, Canada will usher in a new round of epidemic peaks in July.

In the United States, the number of new cases in a single day (7-day average) has exceeded 100,000 for one month in a row, and has yet to show a downward trend, reaching a peak of 120,000.

According to data from the US cdc, as of June 25, the proportion of ba.5 has reached 36.6%, which is close to the proportion of ba.2.12.1 (42%), and will soon become the main strain of the epidemic in the United States.

In Europe, ba.5 has also become the main strain in many countries.

As of June 27, ba.5 accounted for 55%, 59%, and 66% in the UK, Germany, and France, respectively.

The number of confirmed cases in Germany began to rise in early May, and the number of new cases in a single day is now close to 90,000, 3.2 times the previous minimum (May 6).

In Asia, the outbreak in Singapore has also resurfaced.

On July 4, the number of new cases in Singapore in a single day (7-day average) reached 8,500, a 2.65-fold increase from the beginning of June.

Singapore's health minister said on July 5 that the number of patients infected with ba.4/ba.5 doubled every week, initially accounting for only 3% of new cases; it increased to 30% at the end of June, and on July 4, this was A proportion has reached 50%. He predicts that by next week, ba.4/ba.5 will become the main strain in Singapore, and the proportion of patients will reach 70-80%.

Strong immune escape ability

Compared to other mutant strains, ba.5 spreads faster.

According to a research report released by the Institute of Medical Research of the University of Tokyo, Japan, compared with Omicron ba.2, the effective reproduction number (rt value) of ba.5 is higher, that is, during the infection period, the average number of people a patient can infect More.

According to the research of South African scholars, ba.4/5 has a growth advantage relative to ba.2, and its basic reproduction number (r0) may reach 18.6, which is 5.6 times that of the original strain, 3.65 times that of delta, and Omicron. 1.96 times of ba.1 and 1.39 times of ba.2.

Part of the reason the ba.5 mutant strain is more transmissible is its stronger immune evasion ability. This shows that even if the patient has been infected with other strains of the new crown, or has been vaccinated, ba.5 can still break through this layer of the immune system, resulting in re-infection.

The Institute of Medicine, The University of Tokyo conducted neutralization assay analysis on four sera, including ba.1 sera from recovered patients (not fully vaccinated), ba.1 sera from survivors of breakthrough infection (completely vaccinated and reinfected), ba.2 Infection with recovered sera (not fully vaccinated), with ba.2 suddenly infected with recovered sera (completely vaccinated and re-infected), the neutralization effect of infected sera on ba.5 compared to the previous variant is almost always present significantly decreased.

Research by the Wellcome Centre for Human Genetics at Oxford University in the United Kingdom also shows that ba.5 has a strong immune escape ability.
Within 14 days of infection with the ba.1 mutant strain, the neutralizing effect of the infected serum on ba.5 was much weaker than that of ba.1 and ba.2, 1.9 times and 1.5 times lower, respectively; while after infection with the ba.1 mutant virus After 21 days of the strain, the neutralization of ba.5 by the serum of the infected person declined more sharply, 3.4 times lower than that in the face of ba.1, and 2 times lower in the face of ba.2.

The same applies to vaccinated patients, and the effects of different vaccines vary.

The researchers observed that after 28 days of inoculation with three doses of the Oxford/AstraZeneca new crown vaccine, the neutralization effect of the infected person's serum on the ba.5 virus decreased by 2.1 times compared with ba.1 and decreased compared with ba.2 1.8 times.

And 28 days after inoculation with three doses of Pfizer Biotech's new crown vaccine, the neutralization effect of serum decreased even more. Compared with ba.1 and ba.2, the neutralization effect of serum on ba.5 decreased by 3.2 times.

According to reports, my country's first imported case infected with ba.5 has received 4 doses of the new crown vaccine in China and Uganda before infection.or more pathogenic

In addition to its strong immune evasion ability, ba.5 may also be more pathogenic than other mutant strains.
This pathogenicity is reflected in many aspects, including varying degrees of influence on body weight, blood oxygen concentration, bronchi, and alveoli.
According to a report from the Institute of Medical Research at the University of Tokyo, based on research on hamsters, ba.5 is more likely to spread in the lungs and periphery of infected hamsters than ba.2. After 3 days of infection with ba.5 virus, the RNA level around the lungs of hamsters was 5.7 times that of ba.2 virus infection; after 5 days of infection, the RNA level of ba.5 was still 4.2 times that of ba.2.

Therefore, the ba.5 variant strain is more likely to cause bronchoconstriction or airway obstruction in hamsters. Within a week, hamsters infected with ba.5 were more likely to experience shortness of breath, decreased subcutaneous oxygen saturation, and increased enhanced respiratory intervals.

At the same time, the ba.5 mutant strain was also more likely to cause bronchitis, alveolar damage, and lung congestion/bleeding in infected hamsters.

In addition, compared with ba.2 and ba.2.12.1, ba.5 caused a greater reduction in the weight of hamsters within a week, about 10%, while the weight of hamsters infected with the remaining strains increased.

Of course, these pathogenicities are only reflected in experimental hamsters and cannot be directly deduced to human infected individuals, and there is currently no data to suggest that ba.5 causes more severe symptoms.
However, judging from the current epidemic situation in Portugal, the impact of the ba.5 mutant strain cannot be ignored.
Affected by the ba.5 strain, Portugal entered this round of epidemics at the end of April and peaked at the beginning of June. The number of new cases in a single day was close to 30,000, and it has gradually declined since then, and is currently at the end of this round of epidemics.

Although the number of confirmed cases is less than the previous round of the epidemic (end of December 2021 to early March of 2022), the peak of new confirmed cases in a single day is more than doubled, but the peak of new deaths in a single day is higher than the previous one round of epidemics. On June 20, the number of new deaths in a single day in Portugal was 56 (7-day average), while the peak of new deaths in a single day in the previous round of epidemics was 52.

At the beginning of May, the European Center for Disease Control and Prevention (ecdc) had listed ba.5 as a "mutant strain of concern" and called on countries to be vigilant against it. Although ba.5 may not cause severe disease, it will still affect the Burdens on hospitals and intensive care units. At the same time, ecdc also emphasized that increasing the vaccination rate and promoting the vaccination of the third booster needle can still achieve a certain protective effect.

Everyone should protect themself with necessary disinfecting products.  such as alcohol and disinfectant wet wipes, disinfecting spray products.