Pfizer booster study lifts mood over Omicron variant

In preliminary results published on Wednesday, the US and German companies behind one of the world's foremost shots to combat Covid-19 said a booster generated around the same level of potent antibodies against Omicron as is seen after a second dose with the initial strain.

But they warned that "the Omicron variant is probably not sufficiently neutralised after two doses."

The announcement, which has not yet been peer reviewed, was called reassuring by experts, and came as the first independent data from labs around the world emerged, indicating the new mutations are better at evading immunity from infections and vaccines than those before them.

"We still need to be very measured and take a wait and see approach, but I think what we do have is at least encouraging," virologist Angela Rasmussen of Canada's Vaccine and Infectious Disease Organization said.

Blood samples from around 20 people who had received two doses of the current vaccine showed on average a 25-fold reduction in neutralising antibodies compared to the early strain of the virus, the companies said.

But they added that another part of the immune response -- from T cells -- were probably still effective against the new variant, meaning that people with two doses "may still be protected against severe forms of the disease".

The vaccine-makers are developing an Omicron-specific version of the jab, which they hope will be ready by March, but say the decision whether to mass produce it would depend on the variant's spread.