The World Health Organization (WHO) recently said the highly mutated Omicron COVID-19 variant could change the course of the pandemic, though its exact impact is "still difficult to know".

"Certain features of Omicron, including its global spread and large number of mutation, suggest it could have a major impact on the course of the pandemic. Exactly what that impact will be is still difficult to know," said WHO Director-General Dr. Tedros Adhanom Ghebreyesus during a press briefing on Wednesday.

"We are now starting to see a consistent picture of rapid increase in transmission, although for now the exact rate of increase relative to other variant remain difficult to quantify," he continued. Genetic changes to the virus affect its virulence, possibly indicating that it can be more infectious than previous strains, according to the global health agency.

Tedros added that new data on Omicron are emerging every day, but scientist need more time to complete studies and interpret the results. "We must be careful about drawing firm conclusion until we have a more complete picture," he added.

For now, it seems that Omicron may affect the efficiency of currently available COVID-19 vaccines, including the mRNA-based shots developed by Pfizer (PFE  )-BioNTech (BNTX  ) and Moderna (MRNA  ).

Pfizer and BioNTech announced last Wednesday that a third dose of their vaccine increases antibody protection levels comparable with the 95% protection provided by two doses against the original COVID strain, according to a preliminary lab study, signalling possible high protection against Omicron.

"Although two doses of the vaccine may still offer protection against severe disease caused by the Omicron strain, it's clear from these preliminary data that protection is improved with a third dose of our vaccine," Pfizer CEO Albert Bourla said in a joint statement with BioNTech.

"Ensuring as many people as possible are fully vaccinated with the first two dose series and a booster remains the best course of action to prevent the spread of COVID-19," Bourla added.

The data comes from a small, preliminary lab study by South African scientists that found the Omicron variant evades the protection provided by antibodies to a significant degree in blood samples taken from participants who were fully vaccinated with the Pfizer-BioNTech vaccine.

The two companies will have enough data by the "end of the month" to determine whether or not only a booster shot is needed to protect against Omicron of if the pair needs to develop a new vaccine, Bourla said. Pfizer and BioNTech expect to have a vaccine that specifically targets Omicron available by March 2022.