Omicron shows a growth advantage over delta and is expected to become the main variant in the UK

British Prime Minister Boris Johnson stated that the UK is under a “wave” of new coronavirus disease (COVID-19) cases related to the new variant omicron. 

According to official data, the country recorded 1,239 new omicron cases on Sunday, bringing the total number of mutations across the country to 3,137. According to health experts, the biggest concern is that the latest mutation may make two widely used vaccine candidates—Pfizer and AstraZeneca—become less effective. 

The British Health and Safety Agency (UKHSA)'s risk analysis of omicron classified growth advantages and immune evasion into the "red" category, infectivity into the "amber" category, and did not classify the severity of infection due to insufficient data. The health agency raised the overall COVID-19 alert nationwide from "4" to "5". 

According to UKHSA, the new "Variation of Concern" (VOC) shows "growth advantages over the Delta variant", which basically means that it may take over and become the country's main variant. 

The health agency pointed out that immunity derived from vaccines and natural infections significantly reduces the ability to prevent omicron infections. In its communicable factory, it stated that the new VOC is "at least as communicable as delta." 

The national health agency wrote that it is awaiting data on serious diseases, but in preventing serious diseases, vaccines are more effective than mild infections in the case of previous mutations.

The report issued on December 10, 2021 stated: 

Compared with the early pandemic virus, the neutralizing activity of Pfizer's 2 doses of vaccine serum on omicron was reduced by 20 to 40 times. It was observed that the activity of the AstraZeneca 2 dose serum was more reduced, and for a high proportion of such serum, the neutralizing activity was below the limit of quantification in the assay.

However, the report shows that Pfizer's booster injection "regardless of the type of primary vaccination" will result in an increase in neutralizing activity, reaching 70-75%. 

The UK will start boosting injections for people over 18 years old this week, three months after the second injection. 

Currently, 68% of the country's population is fully vaccinated, while 6.6% of the population is partially vaccinated. In the past 7 days, the number of weekly cases and deaths has risen by 12% and 1%, respectively. 

"It will take several weeks to estimate the effectiveness of (vaccine) for serious omicron diseases. However, based on this experience, it may be much higher than the estimate for symptomatic diseases," UKHSA points out.

Vaccine efficacy analysis was performed on 56,439 delta and 581 omicron cases. The number of omicron cases is still less than that of delta, but if new VOCs continue to spread at the current rate, there is concern that it will stabilize the delta prevalence by mid-December. 

The report shows that few omicron cases in the country have travel history or meet with people with travel history, which implies community transmission. The analysis showed that reinfection increased by a factor of 3-8—7% (25 out of 361) omicron cases and 0.4% (336 out of 85,460) delta cases were reinfection.

According to data from the British health agency, although this is still early data, household transmission between omicron and delta has also increased significantly-19% of omicron cases lead to household outbreaks, compared with 8.5% of delta cases. 

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