[MMaschin]

The difference is between antibodies and T cells.

Antibodies have been show to last for around 7-11 months after infection. They don't know how long T cell reactions will last, but those who recovered from SARS have shown T cell response to Covid-19 17 years after recovery.

Antibodies can prevent a virus from infecting a cell, while T cells (white blood cells) recognize an infected cell and kill it. They also generate antibodies when they attack an infected cell.

So, without antibodies you still might be able to be infected, but if you have T cell reactivity your body will be able to quickly fight it off.

There is speculation that one of the reasons that so many people have asymptomatic Covid-19 is that they were exposed to SARS back in 2003 and had T cell immunity.

[the OlLine Rebel]

Thanks for explanation! Hope I can understand.