Scientists urge caution on use of lateral flow tests to screen for Covid-19
useful info here for anyone picking up students from Uni returning home for Christmas who are taking LFD tests -- lateral flow tests.
use only as a guide. a sensible approach from my brother in Law who has both sets of elderly parents coming for Xmas is that both sets need to properly isolate for a week before coming, thus protecting all and reducing risk.
Similarly a student returning home, even with a negative test should remain 'distant' for the first week.

"Jon Deeks, a professor of biostatistics at the University of Birmingham, said that the test is ‘entirely unsuitable’ for community testing, such as that planned for university students in the run-up to Christmas. ‘As the test may miss up to half of cases, a negative test result indicates a reduced risk of Covid, but does not exclude Covid,’ Deeks added. ‘This evidence raises serious concerns that the benefits are likely to be few, with serious risk of harm if the public are misled by unjustified government claims of this test’s high performance.’
 Deeks pointed out that the report’s headline figure of 76.8% sensitivity mixes data from different settings. One study of Innova’s device at a testing centre found that the device appeared to miss one out of every two Covid-19 cases (58%). Another study using nurses to test patients suggests it missed one out of every four cases (73%)."

there are more enthusiastic articles and research which i shall add below, but it would seem these tests are a 'guide' and should not be considered definitive -- as with so much Covid info!!

https://www.chemistryworld.com/news/scientists-urge-caution-on-use-of-lateral-flow-tests-to-screen-for-covid-19/4012763.article


this is one of the source papers https://www.bmj.com/content/371/bmj.m4262

and this is a readable extracthttps://www.ox.ac.uk/news/2020-11-11-oxford-university-and-phe-confirm-lateral-flow-tests-show-high-specificity-and-are#

this is the more negative evaluation https://www.bmj.com/content/371/bmj.m4323

 the following article identifies how, although antibodies may diminish in months, they are not the 'whole story'; how the 'memory response is more important and how some vaccines may better be able to give a long immune memory

IMMUNE MEMORY IS MORE IMPORTANT

"Antibody responses are usually short-lived because once they have done their job you don't need them," said Jonathan Stoye, head of virology at Britain's Francis Crick Institute.

"But that doesn't mean that immunity, either induced by infection or by vaccination, is necessarily short-lived: Memory cells can respond to and combat a new infection."

Since SARS-CoV-2, the virus that causes COVID-19, is a new human virus, scientists don't yet know what levels of immunity will turn out to be protective. But many of the vaccine makers are touting both the antibody and T-cell responses, which are increasingly seen as important to lasting immunity.

"The immune system is very complicated. We know antibodies are important, but they're not the whole story," said Lawrence Young, a professor of molecular oncology at Britain's Warwick University. "The important thing here is immune memory."

Key to the process of immunity are memory cells known as T- and B-lymphocytes. Having made antibodies to a certain virus in an initial infection, the body uses these cells to remember that pathogen, "so when you are next exposed to the virus, the antibody response kicks in much sooner", Young said.

With vaccines, a key feature is that scientists developing them can select as targets the most important bits of the pathogen - in COVID-19's case these include the so-called "spike protein" on the surface of SARS-CoV-2 virus - to get the strongest and most lasting memory responses from T and B lymphocytes.

Some vaccines also contain stimulators or boosters, known as adjuvants, which can supercharge the response, and others are designed to be given in multiple doses to ensure higher concentrations of antibodies will create stronger memories.

"The idea is that while the natural infection may give you poor memory that may not last, the vaccine will give you strong memory that does last," said Danny Altmann, a professor of immunology at Imperial College London.

   https://www.medscape.com/viewarticle/939994

excellent graphic displays of aerosol and ventilation in enclosed spaces with differing contact times and use of ventilation



https://english.elpais.com/society/2020-10-28/a-room-a-bar-and-a-class-how-the-coronavirus-is-spread-through-the-air.html