It normally takes 10 year period to trial and develop an effective vaccine against disease. in 2020, scientists managed to develop multiple vaccines within the time frame of a single year.
Some clarity is needed in regards to fighting disease. 70% effective vaccines (in clinical trials) such as AstraZeneca and the Johnson & Johnson are effective in stopping COVID-19. While both the Pfizer/BioNTech and Moderna vaccines are 94 to 95% effective, the AstraZeneca and Johnson & Johnson are none the less sufficient in combatting the disease. In this regard the percentage effective argument is irrelevant. Their benefits over the Pfizer and Moderna are outlined below.

The first vaccines receiving EUA (emergency use authorisation) in the US are the Pfizer/BioNTech and Moderna vaccines and are mRNA vaccines. Both require two doses.
AstraZeneca and Johnson & Johnson vaccines in contrast are viral vector vaccines. AstraZeneca has received EUA in Australia and Johnson & Johnson has now received EUA in the US.

mRNA stands for messenger ribonucleic acid and could be described as giving your body instructions to construct a particular protein. mRNA is not able to modify a person’s genetic makeup or DNA. mRNA from the vaccine never enters the nucleus of the cell (location of the DNA). Instead, the COVID- 19 vaccines that use mRNA work with body’s natural defence to develop immunity to the disease.

Viral vector is a gene code unique to SARs-CoV-2 and helps produce a spike protein and displays it on the cell’s surface. Once on the surface of the cell, it causes the immune system to begin producing antibodies and activating T-cells to fight off what ‘it thinks’ is an infection.

Like the AstraZeneca, the Johnson & Johnson vaccine does not require ultra low temperature storage and can cater for innumerable situations where sub zero storage is unfeasable.
Obvious advantages especially for developing countries and for increased rates of vaccination and ultimately potential for herd immunity in population.
Prior war efforts in converting factory floors to accomodate and ramp up production is analogous to recent pharmaceutical companies in their effort to combat COVD- 19. Known as second-source agreements, smaller companies in developing countries have paired up with vaccine companies in rich countries to produce faster rollout times.