The video clip was released a day after her sister, Kim Kardashian West, drew hefty criticism for celebrating her lavish 40th birthday vacation with a large group.
The antigen test for the coronavirus is not seen as being as reliable as the so-called "PCR test", in which a sample taken from a nasal swab is sent to a lab for testing.
GSK shares were down 1% at 1,347.2 pence after the drugmaker's shingles vaccine Shingrix, the biggest driver of sales growth last year, saw quarterly revenue fall 30% from a year earlier.
What we saw through the quarter ... were definitely lower vaccination rates in July and August.
Euro zone shares fell and London's FTSE 100 dropped to its lowest level in six months. The dollar index rose around half a percent as investors sought safety.
The EU's chief negotiator, Michel Barnier, is in London for negotiations, after which the talks will continue in Brussels.