Yes here where I live proof of antibodies is quite acceptable for travel or whatever. This is a good article:-
Quit Ignoring Natural COVID Immunity — Antibody testing and proof of prior infection can allow more people to return to normal by Jeffrey Klausner, MD, MPH, and Noah Kojima, MD May 28, 2021
Epidemiologists estimate over 160 million people worldwide have recovered from COVID-19. Those who have recovered have an astonishingly low frequency of repeat infection, disease, or death. That immunity from prior infection protects many people now where vaccines are not yet available.
... Like many aspects of the Federal Government's response to COVID-19, the FDA's comment lags behind the science. Given that 90% to 99% of people who recover from COVID-19 develop detectable neutralizing antibodies, doctors can use the correct test to inform people of their risk. We can counsel patients that those who have recovered from COVID-19 have a strong protective immunity, protecting them from repeat infection, disease, hospitalization, and death. In fact, that protection is similar to or better than vaccine-induced immunity. Putting that together, people who have recovered from prior infection or those with detectable antibodies should be considered protected, similarly to someone who is vaccinated.
Moving forward, policymakers should include natural immunity as determined by an accurate and reliable antibody test or the documentation of prior infection (previous positive PCR or antigen test), as evidence of immunity equal to that of vaccination. That immunity should be given the same societal status as vaccine-inducted immunity. Such a policy will greatly reduce anxiety and increase access to travel, events, family visits, and more. The updated policy will allow those who have recovered to celebrate their recovery by informing them of their immunity, allowing them to safely discard their masks, show their faces, and join the legions of those vaccinated.
https://webcache.googleusercontent.com/search?q=cache:zXvnXSvpw-gJ:https://www.medpagetoday.com/infectiousdisease/covid19/92836+&cd=1&hl=en&ct=clnk&gl=im