Q: Can the order of the authors be changed after the ethics committee approval and before completing the study?

First up, this is an unfortunate but not uncommon situation. Also, there are several considerations involved. So, we shall discuss them one by one.

Before diving into that though, it must be noted that you seem both well-informed and capable. Well-informed, as you seem aware of many elements of research and publishing (such as the manuscript writing process, protocols to follow, and order of authorship) even while being at an early stage of your research career. Capable, because you came up with an idea that the HOD liked enough to want to claim ownership and authorship of. So, kudos on both accounts. Hopefully, this can be a silver lining of sorts in this situation.

Now, let’s get to discussing the various matters in the situation.

• Authorship criteria: As you seem quite well-informed about authorship, you may know of the criteria established by the International Committee of Medical Journal Editors (ICMJE), an industry body that makes recommendations around writing, editing, and publishing scientific manuscripts. If not, you may go through them here. As per the ICMJE guidelines, to qualify as an author, an individual has to fulfil all four criteria. By this measure, and from what you have described, you are an author, but the HOD is not.
• Authorship issue: Technically (and ideally) speaking, there should be no issue of (order of) authorship for this manuscript, as there is only one author: you. However, as the HOD has insisted that he be included as an author, that too, the first author, an issue obviously arises. Also, you have mentioned that you are presently not even the second author but the third author. I assume then that the second author is your supervisor (preceptor). In that case, this scenario becomes one of both coercive authorship (with the HOD forcing you into including his name) and honorary authorship (with you having to include the supervisor as an author and even relinquishing the second authorship to them). As already observed, these are unfortunate but not infrequent situations given the tremendous pressure to publish felt by both junior and senior researchers.
• Authorship determination: Even in this case, technically, you should be the first author and the HOD should be the corresponding author. The corresponding author is responsible for communicating and coordinating with the journal, and is typically a person of authority and under whose aegis the research is being conducted. From what I understand of the supervisor’s contribution, they can be a non-author contributor on the paper. Again, see the ICMJE guidelines defining non-author contribution here. In other words, they should be mentioned in the Acknowledgments section, and not on the title page.
• Authorship resolution: Resolving this in all likelihood not be easy, if not improbable. So, we would urge you to adopt a more pragmatic path, especially given that you are in the early stages as a researcher and have a long way to go. Also, you would be well aware that the supervisor will be involved in your internship evaluation and certification, with inputs from the HOD. Any conflict at this stage is unlikely to go down well with them and may result in an undesirable evaluation. With that in mind, we have discussed various possibilities below, which are also responses to your queries.
• Journal course of action: You have asked whether it is possible to change the order of the authors while publishing. We understand this means that you would like to change the order during the revision and finalization stages of publication without informing the HOD. If you do this, as you can understand, the HOD will eventually come to know about this when the article is published, leading to a potentially negative outcome for your internship work. Also, when the journal editor comes to know of the change in authorship, they will need a signed form by all authors of the manuscript agreeing to the change, which in this case includes the HOD and the supervisor. Additionally, the editor will not proceed with the next stage until the issue is resolved, resulting in a delay in publication.
• Ethics committee certificate revision: You have asked whether you can change the order in the ethics committee certificate. The contents of the certificate and the regulations of the ethics committee (or institutional review board, as it is also called) differ from institute to institute. So, we may not be privy to the exact process with your present institute. However, this is likely to take time to resolve and revise, involving all parties (again, including the HOD and supervisor) and perhaps also the director of the institute, as the director needs to sign on the certificate. Again, there may be unfavorable consequences for your internship and also a delay in publication.
• Discussion with supervisor and/or HOD: Your final query was about you seeking to claim your work. While some of the points we have just discussed may have you feeling despondent, you could still seek to have a discussion with the supervisor, HOD, or both. If so, you could begin with the supervisor to get a ‘feel’ of how this is likely to be taken by the HOD. Of course, as we have already indicated, you would need to be judicious both in what you discuss and how you go about it. Of course too, from what you have described, the HOD is unlikely to yield. So, at best, you can have a polite, fact-based discussion and leave it at that. You would have done your best given the circumstances, and as mentioned at the outset, you have already done well by coming up with what seems like a novel idea for research.

We will leave you with this post that discusses various angles but makes the same observation: authorship issues are not uncommon and not easy to resolve. For more perspectives on the issue, you may also go through the following resources:

• When authorship goes wrong
• Should my professor be the first author of my research?
• Is it possible to remove a co-author from a published article?
• Authorship and conflicts of interest from a journal editor's standpoint

You will no doubt gain from this experience and know better how to handle such matters in the future. For now, all the best for your internship and for the next stage in your career!