It was thought that it was very bad at inducing neutralizing antibodies, although recently there are lots of studies looking at patients who are chronically infected, who do actually make pretty good neutralizing - broadly neutralizing - antibodies, but it’s too late for them. They can take 3 to 5 years before they come up. One of the problems is that the first antibodies that are made are not neutralizing. Within two weeks of infection people will make some antibodies to parts of the virus - the envelope protein - but they are non-neutralizing. And then there’s a rather long period before they make antibodies that will neutralize the autologous or infecting virus - that’s about 80 days. Then it may be years before they make antibodies that broadly neutralize many different viruses. The reasons, I think, are partly that there are many sites where the antibody seems to bind to but doesn’t effectively neutralize. There are many sites where the virus just varies - where it has variable loops - so that the antibodies might neutralize that virus, but it can very easily escape by mutation. And then there are relatively few sites that are highly conserved, which the virus can’t really change without big fitness costs, such as the CD4 binding site which it uses to infect cells [1]. It seems to be very hard to get antibodies to those sites. They do come up in some patients after 3 to 5 years, but these antibodies are very mutated from their germline ancestor antibodies. There’s been a lot of selection over several years. So sometimes they accumulate 50 somatic mutations before they acquire the specificity and affinity of a broadly neutralizing antibody. But even then they are a minority population in all the antibodies - they’re mainly present at under 1% of all the antibodies being made. The challenge is to design a vaccine that will somehow induce lots of these protective antibodies [2]