By shortening the administrative gaps between the trials, which are standard in the industry, you remove reporting time to look at side effects that may not be immediately apparent - often in the Pharma industry projects get canned or altered because issues are flagged up.
The long drawn out process is not scientific time, but does give the opportunity for unforeseen complications to flag - in the case of the Covid vaccine, myocarditis, for example was not detected initially, had there been the usual gaps in the procedure it would have been detected, meaning it could have been included in the patient information BEFORE the first round of vaccinations.
What happened was that the product was deployed and the artefact was discovered later, meaning patients didn't have full informed consent and physicians didn't know the risk profile.
mRNA is not a new concept, it was first developed as a concept in the 1970s, but the first time it was employed commercially and used in humans was the Pfizer covid vaccine.
One of the scientists who developed mRNA, Robert Malone, cautioned against using the vaccine so widely, across all age groups regardless of risk profile - he was pilloried, but quite right, had there been some monumental issue with it you would end up condemning everyone.
A huge mis step was taken in trying to force people to take the vaccine on the predication that it would stop the spread, transmission was never part of the brief given to the Pharma companies and no serious trials were run. It would have needed to have an almost sterilising effect to significantly impact transmission of this class of virus.
Looking closely at the data, it is still up for grabs whether the vaccine actually has any real preventative effect. At the same time as the vaccine was deployed, SARS CoV2 did what all zoonotic virus' that cross into the human population do, it mutated its form for best effect in humans, becoming not a zoonotic but a human virus, and these typically are better dealt with by our immune system. Its high transmission rate meant much of the population already had conferred natural immunity, and so the death rate started to subside - this is how every previous pandemic ended, in a similar time frame, so it's impossible to accurately gauge the vaccine impact.
mRNA potentially is a very good technology, but in this case, it was used rashly, the public poorly informed and politicians bamboozled into bad decision making, which has wrecked the economy and seriously damaged the health service and many peoples trust in medicine.
Many have gone down conspiracy rabbit holes, or entrenched positions for and against, all of which is dangerous to public