This photo image shows a World Health Organization (WHO) logo on an Android phone.

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World Health Organization officials said they are still trying to understand why the Delta variant is more transmissible and potentially making people sicker than the original strain of coronavirus.

“We’re really trying to better understand why the Delta variant is more portable,” said Dr. Maria Van Kerkhove, WHO technical director for Covid-19, at a press conference on Friday. “There are certain mutations in the Delta variant that allow the virus, for example, to attach itself to a cell more easily. There are some laboratory studies that suggest that there is increased replication in some of the human respiratory systems modeled.”

In the past few weeks, new data on the highly transmissible strain has emerged around the world as scientists try to better understand the new threat. The Centers for Disease Control and Prevention warned lawmakers Thursday that new research suggests the Delta strain is more contagious than swine flu, the common cold and polio. It’s as contagious as chicken pox. It also appears to have a longer transmission window than the original Covid-19 strain and can make the elderly sicker even if they have been fully vaccinated.

Thursday’s warning came in a confidential document that was reviewed by CNBC and authenticated by the federal health authority.

“The virus itself is, as it begins, a dangerous virus. It is a highly transmittable virus. The Delta variant is even more, ”said Van Kerkhove. “It is twice as transferable as the ancestral tribes.”

WHO officials expect other dangerous variants to emerge as countries struggle to distribute the life-saving vaccines to their populations.

“They get fitter the more they circulate, and therefore the virus is likely to become more transmissible because they develop in such a way that they change over time,” said Van Kerkhove.

She said it is imperative that nations follow public health measures like social distancing and the wearing of masks as nations distribute more vaccines around the world, especially those with the lowest vaccination rates.

We need “around 70% coverage worldwide to really slow down transmission and reduce the risk of new variants appearing,” said Dr. Bruce Aylward, Senior Advisor to the WHO Director General.

However, given current trends, health professionals are not optimistic. “This will not be the last variant of the virus you will hear us talk about,” said Van Kerkhove.