Not yet. Although at Chinese insistence, after China blocked the original phase 2 studies in China proposed by the WHO, there is some vague talk of broader studies in the [new] WHO draft proposal like
Coronaviruses phylogenetically related to SARS-CoV-2 have been discovered in Rhinolophus species (horseshoe bats) around the world, particularly in South-East Asia. Retrospective tests of samples collected from Rhinolophus bats should be carried out globally and in particular in Asia and South-East Asia.
Although I should say that 90% of the concrete proposal in that draft still focus on studies in China (too many to quote, really, at least 10 bullets/paras).
And since those are blocked, the WHO now is now embroiled in a controversy whether they are even doing anything [concrete] at all in those origin studies regards.
The Western scientific community has taken a very dismal view of most of those Chinese alternative-theory proposals/views/papers [on this], with phrases like "smoke and mirrors", "childish lie[s]", and "bullshit" being uttered about them, in less official contexts.
Frozen meats/produce, seemingly one of the favorite alternative theories coming from China as to how the virus got there, isn't included/mentioned in the revised WHO draft, as far as I can tell.
Regarding the retrospective antibody studies [added to the Q in an edit], the draft WHO proposal has this to say, in essence "work is currently ongoing" on "verification and/or validation"
In addition, the SAGO has reviewed publications with findings of SARS-CoV-2 detection in biological and environmental samples in 2019 from different parts of the world (Table 3). In some cases, such as in Italy, France and the United States, verification and/or validation has been initiated by WHO through the help of external laboratories. This work is currently ongoing (Montomoli et al., 2021). The SAGO supports further investigations in any part of the world where there is firm evidence of SARS-CoV-2 virus activity before the recognized outbreak in Wuhan in December 2019. This should also be considered in other areas where there has been evidence of early SARS-CoV-2 activity (see some examples of studies in Table 3).
And as a cautionary tale why verification might be need, they also say this (a little bit before)
The SAGO was also presented with new unpublished serologic results by Chinese scientists of more than 40 000 stored samples from blood donors in Wuhan who provided blood between September and December 2019 (Chang et al., 2022). These samples were reported to have been tested for antibodies to SARS-CoV-2. More than 200 samples proved positive (by ELISA), however, none were positive upon using a confirmative assay (by serum neutralization assays). Other samples collected in Wuhan prior to December 2019 were reported to be negative on retrospective serological testing. The SAGO has requested further information on these data and the methods used to analyze these samples.
That table 3 spans like 4 pages, so I won't even try to squeeze it here. But there's a 2nd para about that table:
The SAGO has begun to evaluate studies that have published results indicating SARS-CoV-2 positive samples collected prior to December 2019. Table 3 lists studies that have suggested the possible detection of SARS-CoV-2 in stored samples prior to the start of the outbreak in those countries. The SAGO notes that the methods of each study with results indicating positive samples in 2019 requires further validation and verification and thus the significance of these findings remains unclear. The SAGO is currently reviewing these studies and the methods used to identify the positive samples and will provide further information in forthcoming reports to WHO.
And at the bullet/recommendation level that's abstracted to
With WHO coordination, a comprehensive verification exercise of any detection of SARS-CoV-2 from biological samples from 2019 should be continued worldwide.
And now that I look more carefully they do say something about preserved foods, but not [explicitly] frozen ones, although one might read as included in "etc.":
There should be particular attention to culling activities before or after the first detection of SARS-CoV-2 in humans. Animal products, either preserved (dry, smoked, fermented, sausages, etc.) or potentially stored from culling activities or animal products from the period before the outbreak should be identified and tested. Humans employed in breeding facilities or in the downstream exploitation chain should be identified and serologically tested. Sera from such persons should be shared with international laboratories for external verification.
No country (China or other) is mentioned in that para, as you can see.
But as some kind of conclusion here, the WHO doesn't seem geared up to do much investigation themselves. They mostly review others' findings and make recommendations, at least on these matters, and in that report. The breadth of recommendations also makes it hard to tell which ones they might consider a priority. However this situation doesn't seem atypical. A little googling found that:
While the WHO did offer some normative leadership during the Ebola outbreak, as per its constitution, it did not provide an effective operational response, yet nor did it have a mandate to do so. This division between the normative and operational was further highlighted by the discrepancy between what the global community expects the WHO to do in a health emergency, and what it is able to do with its financial and organizational constraints.
