It is just over four months since the variant was first discovered in South Africa.

Since then, it has spread around the world.

The first Swedish cases were found at the beginning of May, and since then things have gone quickly.

Last week, BA.5 accounted for 17.3 percent of all fully sequenced cases, according to the Public Health Agency's preliminary statistics.

One week later, the share had grown to 31.8 percent.

Rapid increases have previously been observed in several countries in Europe, including Germany and the United Kingdom.

The variant became dominant early in Portugal and recently also in Denmark.

Poorer protection of the vaccine

The fact that BA.5 spreads so fast and displaces the older omicron variants BA.1 and BA.2 is assumed to be due to the fact that it has mutations which mean that the virus cannot be controlled as easily with antibodies from vaccines or previous infections.

This also applies to the BA.4 variant, which is also widespread in Sweden to some extent.

According to a recent study, the antibody response in newly vaccinated individuals is much weaker against all omicron variants than against the original SARS-Cov2 virus - and within the omicron family, the antibody response is only a third as strong for BA.4 and BA.5 as for BA.1 and BA. 2.

"Our data suggest that the new omicron variants are likely to lead to an increase in infections in populations with high vaccination rates and high levels of natural immunity to BA.1 and BA.2," writes one of the researchers, Dan Barouch, in an email to CNN.

The spread of infection is increasing in Sweden

In Sweden, the number of confirmed cases of infection has increased in June after having decreased for several months before that.

Last week, a 37% increase was noted compared to the previous week.

Among people with home care, the increase was 41 percent.

The new omicron variants so far seem to give about the same symptoms as BA.1 and BA.2, ie milder than the original virus.

An as yet unpublished study from South Africa indicates an equally high risk of hospitalization but somewhat less mortality, writes the journal Nature.

Japanese researchers, on the other hand, have concluded that BA.4 and BA.5 may have developed into a worse variant that more easily infects the lung cells, similar to the variants that dominated before omicrons, writes The Guardian.