Antibody test when you've been vaccinated

[JumperandJacket]

My mum is double jabbed but reluctant to have the booster. She therefore got an antibody test done which came up a very weak positive.

She is now saying that this must mean that she's already had covid.

But how does the antibody test distinguish between antibodies from having had covid and having had the vaccine?

My understanding is that there are different types of antibody test. Some detect antibodies from vaccination and some detect antibodies from actual Covid infection. Professor Tim Spector of the Zoe Covid study app has explained this in a YouTube video, but I can't remember what date.

thank you

The tests for antibodies to the vaccine test for antibodies to the spike antigen (s), the tests for antibodies to an infection test for antibodies to the nucleocapsid (n) - which aren't present if you've been vaccinated but haven't had Covid. The current government one that you can get through the Zoe app doesn't distinguish between them, it just tells you that you have antibodies.

A very weak positive means she has low immunity whether that was from the vaccine or infection.
She needs the booster.

I am immunocompromised and was hospitalised with covid despite being double vaxxed 4 months earlier. They said I had probably got low antibodies.

You can test for vaccine induced "S" antibodies or Covid infection "N" antibodies, some tests are specific for one or the other and some are not.
Some quantify the antobodies and others don't.

This one gives a quantity and an idea of what it means.

Antibody tests can either detect antibodies to the spike protein ('S' tests) which will should be present after vaccination or infection, or to the nucleocapsid protein from inside the virus ('N' tests), following a Covid infection.

Most tests around at the moment seem to be S tests.

You can also get home tests that look a bit like LFTs that test for the presence of types of immunoglobulin following infection or vaccination.

The consensus on what level of antibodies is 'good' seems to be 'nobody knows'!