By Julie Steenhuysen

CHICAGO (Reuters). The Delta virus of SARS-CoV-2 now represents nearly half of all global coronavirus infections. It is a result of uncontrolled spread of this novel coronavirus across many regions of the world. Although vaccines have been able to protect against severe disease and death due to the Delta virus, scientists are on high alert.

Let’s see what we can find:

    DELTA – STILL DOMINANT

    The Delta variant, first detected in India in December 2020, remains the most worrisome version of the SARS-CoV-2 virus.

Delta is classified by the World Health Organization as a Variant of Concern. This means that it can increase transmissibility or cause more severe diseases, and reduce the effectiveness of vaccinations.

    Delta’s “superpower” is its transmissibility, according to Shane Crotty, a virologist at the La Jolla Institute for Immunology in San Diego.

    Delta is more than two times as contagious as previous SARS-CoV-2 variants, according to the U.S. Centers for Disease Control and Prevention. It may have a higher chance of infecting people than previous forms.

    Delta also can cause symptoms two to three days sooner than the original coronavirus, giving the immune system less time to mount a defense.

    People infected with Delta carry around 1,200 times more virus in their noses compared with the original version of the coronavirus. The virus is present in both vaccinated and unvaccinated people who contract Delta. Both can pass the virus on to others.

    In vaccinated people, however, the amount of virus drops more quickly, so they likely spread the virus for a shorter time.

    According to the WHO, Delta makes up 99.5% of all genomic sequences reported to public databases and has “outcompeted” other variants in most countries.

    A key exception is South America, where Delta has spread more gradually, and other variants previously seen as possible global threats – notably Gamma, Lambda and Mu – still contribute to a significant proportion of reported cases.

    DELTA OFFSPRING

    Given Delta’s global dominance, many vaccine experts now believe that all future variants will be offshoots of Delta.

    One notable Delta “grandchild” is known as AY.4.2 and is concentrated largely in the UK, where it makes up roughly 10% of sequenced virus samples.

    AY.4.2 carries two additional mutations in the spike protein, which the virus uses to enter cells. Scientists still don’t know what benefit these mutations may confer.

The UK Health Security Agency designated the AY.4.2 a ‘Variant Under Investigation. Although it doesn’t significantly affect vaccine effectiveness, a preliminary analysis has shown that it is not as harmful to the immune system than Delta. However, there are some indications that it may be more transmissible.

The WHO estimates that AY.4.2 spreads to 42 countries including the United States.

    MORE ON THE WAY?

    Virus experts are closely watching the evolution of Delta, looking for any sign that it has acquired mutations that would allow the highly transmissible variant to pierce the immune protection of vaccines and natural infection.

    Even so, while current vaccines prevent severe disease and death, they do not block infection. Even though the virus has been eradicated, it is capable of reproducing in the nose.

    To defeat SARS-CoV-2 will likely require a new generation of vaccines that also block transmission, according to Dr. Gregory Poland, a vaccine developer at the Mayo Clinic. Poland and other experts agree that the world is still vulnerable until then.