system
Given the following post, respond as if you're commenting on Reddit:
human
Many popular articles say “we don’t know if cov2 antibodies provide immunity”. Are there any cases of known diseases where the presence of antibodies for it do not give a reasonable amount of immunity to prevent sickness or transmittal to others?
gpt
First, let’s emphasize that when scientists say “we don’t know if antibodies protect... “ they are not saying “we know that antibodies don’t”. They’re simply pointing out that the evidence isn’t complete yet. 

Second, let’s point out that those statements are now outdated. We *do* know that antibodies protect, at least under some circumstances (because in the preliminary animal test of COVID vaccines, monkeys have been protected). We don’t formally know what percentage of people have protective antibodies after infection, but the expectation is that it’s pretty high. 

Ok, so actually answering the question - Some viruses that are resistant to protective antibodies include most of the herpesviruses, which can stay latent without offering targets to antibodies and which can spread from cell to cell without entering the extracellular region where antibodies can see them. HIV, which can hide in cell DNA and which has a heavy glycan (sugar) coat covering its surface proteins.  Dengue, which can take advantage of low levels of antibodies to enter new cell types and worsen an infection. 

Note, these are not necessarily always true. Herpes only is hidden from antibodies after it’s set up an infection, so it’s hard to eliminate infection but potentially possible to prevent it. Dengue only can take advantage of enhancing antibodies in a narrow range of conditions, and is neutralized if the antibodies are at high enough levels. 

And of course, antibodies are only one branch of immunity. T cells can also give protection. 

And none of these seem to be true for SARS-CoV-2.  It doesn’t go latent or hide from antibodies. There was early concern about enhancing antibodies, but so far there’s no sign that they’re an issue. So even though we still have some uncertainties about protection against SARS-CoV-2, pretty much everything we’ve learned over the past 6 months has been encouraging, which is why scientists remain optimistic about effective vaccines.