If someone tests positive for antibodies, after how much time is it recommended to retest? We are making a family simcha soon and are requiring those coming who haven't been fully vaccinated and don't have recent antibodies to take a PCR test before coming. The issue is where to draw the cutoff line.
It's clear that the person who tested positive for antibodies 3 weeks ago is fine, but what about someone who was tested on Chanuka or Sukkos or last summer? And does it make a difference whether they were actually symptomatic and tested positive for COVID? I tried Google but couldn't fine any clear guidance on this topic. @biobook
Did you add
@biobook in the Edit? I just came across this post, but hadn't gotten an email ping, so wondering if it happens when editing, or if it's something with my email.
When I looked into this - I think it was a couple months ago - the guidance (CDC and others) was to NOT base decisions about social behavior on antibody level because a) there was no known level of antibody about which we could say above this threshold, you're immune, and b) even if antibodies were low, a person might still be immune due to having memory B and T cells.
But as we get more data, it is clear that most people are not getting reinfected so far, and so the recommendation is to consider TIME since infection, rather than antibody level, if you're trying to get a sense of immunity. One study found that immunity for 95% of people studied lasts as long as 8 months, based on detailed study of antibodies as well as B cells and T cells.
This was officially published a few weeks ago in Science: Immunological memory to SARS-CoV-2 assessed for up to 8 months after infection
https://science.sciencemag.org/content/371/6529/eabf4063 but more informally in the news in November:
https://www.nytimes.com/2020/11/17/health/coronavirus-immunity.html So this seems to imply that immunity lasts at least 6-8 months
after the infection, not 6-8 months after whenever the antibody test happened to be given. So, in theory, there would be no need for an antibody test, if someone had a confirmed case of covid, they've probably got good immunity for the next 6 months.
On the other hand, there have been cases of reinfection, and no studies that I've seen on what antibody levels were in those who were reinfected. And, in general, it's been found that those who had less severe or asymptomatic infections have lower antibody levels, though I don't know if they've looked at their T and B memory cells.
The PCR test also seems problematic. Someone can test negative in the early stage of infection, and then be positive a couple days later when they're at your simcha. Or they can pick up the infection during all the interactions that occur while traveling.
And add to that all the uncertainty about the new variants, and whether the antibodies will be effective against them.
What Dr Fauci and Dr Wallensky have been saying is that now is not a good time for travel and social get togethers with people who aren't part of your current living group, especially considering how close we seem to be to widespread vaccination. I think that's why you haven't been able to find any clear guidance on this topic, because the guidance is that we just don't know yet if it's safe.
If it were my family, I'd be telling them that we're making such an extra special party them and we realize now that it won't be ready before August, so we'll zoom for now, and invite you all to visit in the summer. But I'm sure it's obvious by now that I'm on the low-risk end of the spectrum.