Q: Can I submit a published scientific letter to another journal as an original article?

Straight away, it seems you aren’t happy with the fact that your submitted manuscript was published ‘only’ as a letter with the present journal. If this is the case, the journal editor would have made this suggestion/decision after a careful assessment of your submission. This ‘modification’ decision (modifying the manuscript into a letter) is usually made when the journal believes the article has a basic premise, but that premise hasn’t been fully explored in the current research/article or will need further exploration. When making this decision, the journal almost without fail first shares this with the author, and if the author agrees to this, only then do they go ahead with this modified form of the article. So, you probably gave your acceptance to this, but are now obviously having misgivings about this. However, that’s understandable, but it doesn’t help dwelling on what’s already done.

To answer your question now, no, you cannot, rather, should not submit this published letter to another journal. That would be a clear case of duplicate submission (which would be unethical). To any good scientific journal, the novelty of the paper is paramount, and this would clearly not be the case here. What you can do (and could have done) is to build on the basics in the letter/modified manuscript and see if it translates into another complete, full-fledged paper. If so, you could submit the next/full-fledged paper to this journal (or even to another journal) as a follow-up or elaboration of the scientific letter. However, you may consider discussing this idea with the editor once before starting off on the paper. It may well be the case that there isn’t much in the present idea you are exploring (no matter how many times you view it) and it’s possibly better to explore another idea (learn about finding gaps below) that may well lend itself better to a more complete paper.

For the various points discussed above, here are some links that you may find useful to go through.

• Should I withdraw my manuscript if the journal editor recommends it to be submitted as Letter to Editor?
• Duplicate publications and simultaneous submissions
• How can I judge the novelty of my study?
• Tips on identifying research gaps

Hope that helps. Congrats all the same for the publication of the letter! :) And all the best for your next decisions!