Can Vaccination Provide Protection Against Highly Infectious BA.2 Omicron Variant?

The number of confirmed cases of COVID-19 worldwide has exceeded 470 million, and many European and Asian countries have reported a recent resurgence of the epidemic, mainly driven by newly confirmed cases of the new BA.2 Omicron variant of the coronavirus. This variant has already been detected in at least 40 countries, including the US, the UK, India and Denmark. According to the latest government data, about one out of three COVID-19 cases in the United States are now caused by BA.2.

BA.2 is a sub-variant of the Omicron coronavirus strain. Although it has not yet evolved into a mainstream viral strain since the first case was identified in late 2021, government agencies and scientists are closely monitoring the transmissibility of BA.2 and the effectiveness of vaccines against it to prevent a new wave of the pandemic.

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Common Sub-variants of Omicron – BA.1, and BA.2

Three sub-variants of Omicron have currently been identified: BA.1, BA.2 and BA.3. Among them, BA.1 is the predominant virus found in patients infected with the Omicron variant and it is characterized by the R346K mutation in spike proteins. There is also a BA.1.1 sub-lineage under the BA.1 branch.

The BA.2 sub-variant, which has recently become significantly more prevalent, differs from BA.1 in 28 mutations, and these mutations in amino acids and spike proteins give it a growth advantage over BA.1 and a 33% higher transmissibility than BA.1. 

In terms of reinfection rate, preliminary studies have shown that those who have already been infected with BA.1 are protected from the BA.2 sub-variant for a short period of time. In addition, compared with the current global situation, the percentage of severe disease caused by BA.2 is relatively low.

Can Vaccination Provide Protection Against BA.2 infection?

Concerning the protection provided by the existing vaccines against the BA.2 sub-variant, recent studies have shown that receiving two doses of the mRNA COVID vaccine reduces the risk of contracting BA.1 and BA.2 and developing mild symptoms after infection for about 4-6 months, with the effectiveness dropping to about 10% after 6 months. Nevertheless, after 2-4 weeks of receiving the third dose of the vaccine, the effectiveness of the vaccine rebounds to 70%.

Another Danish study comparing the household transmission of BA.1 and BA.2 has revealed that BA.2 is more transmissible in the home environment, with a 29% chance of family members becoming reinfected with BA.1 and 39% in the case of BA.2.

Moreover, the study has shown that fully vaccinated individuals are more protected against infection with Omicron sub-variants than those unvaccinated, while unvaccinated individuals are also more likely to transmit BA.2 to family members compared to BA.1. 

An analysis by the UK Health Security Agency also found similar vaccine effectiveness against symptomatic disease from both BA.1 and BA.2, with further studies underway. Overall, vaccination is still fairly effective in protecting against infection with the BA.2 sub-variant, but booster doses are needed for further protection.

Written by Kathy Huang/ Translated by Richard Chau

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