The Delta coronavirus variant is now believed to be more transmissible than the common cold or seasonal flu, sparking global concern as countries struggle to vaccinate their populations.

The fast-moving variant is already causing havoc in Australia, with NSW and Queensland fighting to control its spread with lockdowns.

US health officials have declared that “the war [against COVID-19] has changed” because of the highly contagious and most likely more severe variant.

Internal documents from the US Centers for Disease Control and Prevention (CDC) say the Delta variant is “as transmissible as chickenpox” and spreads more easily than the common cold, influenza (including the Spanish flu), Ebola and smallpox.

Obtained by The Washington Post, the CDC briefing notes to staff also said the variant appeared to cause more severe illness than the Alpha or ancestral strains of the virus.

Studies from around the world showed higher odds of hospitalisations, ICU admissions, a requirement for oxygen, and death among those infected with Delta.  The variant was associated with higher viral loads and a longer shedding duration

The health officials concluded that there needed to be an urgent revamp of the public messaging in the fight against Delta and recommended masks for everyone in indoor settings as well as mandatory vaccination for health workers.

At a news conference, Dr Ghebreyesus warned the “hard-won gains” were in jeopardy as more health systems around the world became overwhelmed

“So far, four variants of concern have emerged, and there will be more as long as the virus continues to spread,” he warned.

The Delta variant is now the dominant strain globally, having spread to 132 countries