Current thinking seems to be that a booster will be required within a year. This seems to be based on an observed drop-off in anti-bodies in the vaccinated person. The same phenomenon is observed among recovered patients.

For instance, here is a quote from
https://www.cnn.com/2021/05/21/health/us-coronavirus-friday/index.html

“We have to see how long the protection lasts. We know it lasts at least six months,” This was a statement attributed to US Surgeon General Murthy.

We know a lot about the human body. However, there are many things about the body that we cannot measure. For instance, The study is the best attempt yet to define features of the immune response that can act as a proxy for protection against COVID-19, known as a ‘correlate of protection’, says Daniel Altmann, an immunologist at Imperial College London. “Finding the correlate of protection has really been a holy grail for this disease, as for others. It’s surprisingly hard to do.”

This is taken from
https://www.nature.com/articles/d41586-021-01372-6

The researchers estimate that a vaccine has an efficacy of 50% even if it induces antibody levels 80% lower than those found, on average, in a person who has recovered from COVID-19.

The same study brings up an interesting suggestion that longer-term protection against severe forms of covid can be provided by killer T cells.

As you can see, there is a lot of unknown, but possibly discoverable, facts about covid.

Back to my question: How long do you think covid protection will last with the currently available vaccines?