Vaccine trails are outside my research area.

We should always use odds ratio to evaluate before intervention. This adds the control observation between humans outside a risk zone that is useful in containment preparation and in safety.

Stephen while I agree with you but it is worthwhile to note that  there is a very big difference in absolute reduction of VE when OR is used. To me the RR approach might be more accurate given the fact that during such trial we determining the likelihood that the vaccine will prevent clinical illness.

It is never "illegal" to use odds ratio, but the more accurate relative risk is preferred when the data support that analysis.  You agree that the trial is prospective, in which case you should have the initial serology of the 2 (or more) groups.  After the intervention, allowing for enough time for seroconversion, you will have another observation point for determining the rate of seroconversion.  In this way you have the "rate" of seroconversion for each group: an "incidence" rate if you wish.  This allows you to use the (true) relative risk instead of its estimate (the odds ratio).

If instead of seroconversion as the outcome, you were 'challenging' lab animals with a pathogen, then the same logic is used.  From an initial baseline of 'healthy' animals, you can determine the 'incidence rate' of protection among the two groups, and hence relative risk is again valid (and preferred). 

I'm not sure what "vaccine efficiency" is.  Generally, one refers to vaccine efficacy - i.e., what one can assess in a clinical trial under "ideal" conditions, or vaccine effectiveness - i.e., what one can assess from information about the actual use of a vaccine.  The same concepts, by the way, apply to drugs or other interventions.

When one does a clinical trial then it is a prospective cohort study; and I believe you will find that most people believe that relative risk (really relative protection) should be reported as the vaccine efficacy.  In this situation, you can calculate the risk of disease in the non-vaccinated group (which most likely received a placebo) and the risk of disease in the vaccinated group.  You might find the article in the wikipedia link helpful since it provides the formula for vaccine efficacy and it is the equivalent of 1 minus the relative risk of disease in the vaccinated group, made into a percentage.  

On the other hand, when one tries to calculate the degree to which a vaccine protected under actual use, one usually does not have access to comparable cohorts where one received vaccine and the other did not.  Rather, one generally can know who became ill (the cases), match them to a comparison group that did not become ill (the controls), and determine the number of cases and number of controls that were vaccinated.  That allows you to set up a four-fold table from which you can calculate the relative odds of illness given vaccination; and that can be translated into effectiveness.

It also has been argued that under certain assumptions one might estimate vaccine efficacy even in the absence of clinical trials.  See the attached article by Broome et al.  It gives a detailed description of this approach which, I believe, comes down to being able to make assumptions in which the relative odds approach the relative risk.

https://en.wikipedia.org/wiki/Vaccine_efficacy

Not my field.

It is important to observe that vaccines are immune amounts of genetics materials to quantify in experiment for analysis results and safety in odds ratio analysis gives time for this in safe healthy ways.

Kind Regards!

Jia.....  Completely agree.   The decision-maker is whether you have the true incidence of the (outcome) for each exposed group.  Whether you are measuring sero-conversion, or the results of challenges with a pathogen after vaccination, you should have incidence data, ergo, the RR is preferred.