>>re: immunity -- https://www.theage.com.au/national/scientists-at-odds-after-study-finds-coronavirus-antibody-anomaly-20200410-p54iwm.html

From your citation:

Their study, published this week, has not yet been subject to rigorous peer review, which means the findings need to be treated with caution. Flaws could yet emerge in the analysis and future studies may undermine its findings.

Dr Kizzmekia Corbett, part of an American team now testing a COVID-19 vaccine in humans, called the findings unsurprising.

“This is not news. This is classical respiratory-virus shenanigans. The reason many of them circulate yearly is because of [their] inability to induce protective immunity,” she wrote on Twitter.

Assuming for expediency that this study on Chinese patients had been peer reviewed, and accepting that protection duration varies which is why some vaccinations need repeats: still doesn't change the antibody test correlation to immunity right now so not benefiting from lockdown.

Meanwhile a study from New York suggests 87% of positive patients were asymptomatic. So what's the infected and/or recovered cohort? We simply don't know without testing. Testing offers a rational scientific way out of this mess which is why every scientist on the US Covid task force is saying it. If offered a test, my advice is to grab it: hopefully you're part of an asymptomatic recovered majority who can safely volunteer to help others until they too are safe.