Apparently, timing is utterly crucial, according to an infectious disease epidemiologist.

We are less than a week away from Christmas, and across the country, families are getting excited at the thought of finally spending Christmas together again. Travel plans have been long made, restaurant bookings are in the box and presents and food have been bought in. However, now that the Omicron variant is spreading fast, many are beginning to worry, and wonder if meeting up is really worth the risk. The reality is that anyone testing positive now will be in isolation for Christmas and, although there are currently no restrictions on meeting up, the Government has warned us (again and again) to only socialise 'if it really matters' and to pick our social outings carefully. For this reason, antigen tests (Lateral Flow Tests) are going to be playing a big part of our collective festive season, as we all do our best to keep our friends and family safe and out of isolation for Christmas. However, a leading infectious disease epidemiologist has shared an image showing the timing of when you do them is absolutely crucial. His warning shows just how quickly a negative antigen test can turn positive ... literally within a matter of hours.

A demo of how fast you can turn positive:

Yesterday morning, yesterday lunchtime, yesterday evening, this morning. Do LFTs *just* before meeting up. pic.twitter.com/3zM2rDkoa7 — Billy Quilty (@BQuilty) December 16, 2021

The image, shared on Twitter, pictures four antigen tests. The tests taken in the morning, at lunchtime and in the evening are all negative. However, the test taken first thing the next morning is positive. Epidemiologist Billy Quilty, who shared the image, said this is why we should 'do LFTs *just* before meeting up'. Antigen tests are designed for people who do not have symptoms of COVID-19 but are worried about spreading the virus unwittingly. In other words, if you have symptoms you should do a PCR test. Quilty's warning has struck a chord with many on Twitter, who say they've experienced similar results. One Twitter user revealed: 'My son is a teacher and this happened to him three weeks ago. Negative LFT at 7am, go to school. Positive LFT at 7pm. Could well have been shedding COVID-19 at school for much of the day.' Another one added: 'I was negative on Monday evening, went out to get my booster. Tuesday morning, started getting a tickly throat on the walk home and thought I'd better double check. Speaking to Netmums, Lawrence Young, a virologist and professor of molecular oncology, at the University of Warwick, said people should learn to 'flow before they go.' He said the tests were a quick way of checking in real-time whether or not you are infected and infectious. 'The mantra should be ‘flow before you go’. LFTs are also an important way for folk to ensure that they are safe to enjoy Christmas with their family and friends."