The study, conducted by experts at the CDC, was published in the journal Nature on July 13.

For the clearest analysis, researchers collected blood samples from people who had received three doses of the mRNA vaccine against Covid-19.

After that, experts developed different `pseudovirus` versions (pseudoviruses), bearing the characteristics of each Omicron sub-strain.

However, mRNA vaccines are still safe and effective in the new epidemic stage.

Nurses at Brooklyn Hospital in New York, USA, January 2022.

According to the study’s authors, as Omicron continues to infect, it will evolve into many sub-variants that are more transmissible and more effective at evading antibodies.

It is unclear whether BA.4 and BA.5 will develop from the original Omicron version or not.

Two variants discovered in South Africa in April have quickly spread globally because they possess mutations that make the virus easily attach to human cells.

BA.4 and BA.5 have different effects in each country, depending on vaccination rates, circulating strains and population and social structure (e.g. age, prevention safety measures).

BA.5 has appeared in Portugal, Germany, England, Denmark, France, Austria, Belgium, Hong Kong, Australia, Canada, Israel, Norway, Switzerland, Thailand, Singapore, Vietnam…

Experts say BA.5 has a faster spread rate than the previous Omicron version.

Countries have increased numbers of infections and hospitalizations, but not many deaths.