One of the unexpected bonuses of participating in a vaccine trial was finding an online community of like-minded fellow trial participants. As you might imagine, science nerds are over-represented in these groups, and there has been a lot of discussion about the data coming out of the vaccine trials. Unfortunately, we have not seen official data coming out of the trials correlating antibody levels with protection. They presumably have the data, because they have been taking our blood and following who gets covid, but they haven't released it.
A few weeks ago, Labcorp started offering a version of the Roche semi-quantitative anti-spike antibody test (total antibodies, not just IgG) that maxes out at 2500, which means that those of us who are 6-9 months out are mostly within the range that it can measure. This provides an opportunity to figure out the range of antibody levels, and more importantly to compare them to published ranges of antibodies in those recently recovered from covid.
The data that has been provided by the group shows that the RNA vaccines are similar to each other and likely still protective after 6-9 months, because the antibody levels are still higher on average than the levels seen in those recently recovered from covid. Based on my previous educated guess, it looks like I'm the only RNA vaccine recipient in this (small) data set who is marginal for protection against the B.1.351 (SA) variant. So even without boosters, countries that are mostly using Moderna and Pfizer should have protection against the variants for awhile.