“Some Covid-19 Vaccines Have Shown Remarkable Efficacy”

What meaning can we read into Covid-19 vaccines? 
Vaccines are less dangerous portions of disease-causing agents which are given to people to make them capable of staying healthy when exposed to the disease causing agent again. That is, they would not fall sick if they encounter the disease causing agent again. The Covid-19 virus for example, is a disease causing-agent which has caused a global outbreak, affected virtually all countries in the world. A vaccine against Covid-19 normally would teach our body to fight the virus thereby preventing us from catching the Covid-19 virus. This is the most desirable solution because virtually everybody is still vulnerable to Covid-19. Unfortunately there is no globally accepted vaccine for Covid-19.
Media reports show that many countries are already administrating a vaccine against Covid-19. On what basis is that done?
A few countries including USA, Russia, China and Britain have separately developed highly promising vaccines which have been approved for use in these countries. The development of vaccine must follow highly standardized and well controlled steps which must be strictly followed to ensure efficacy and safety. There are laid down values for developing vaccines which must be followed by all vaccine developers. There is, for example, a World Health Organisation (WHO) Standardization of vaccines for Coronavirus disease (Covid-19).
Are these vaccines effective and at what percentage?
Currently the WHO has not validated, approved or recommended any Covid-19 vaccine for global use. A number of Covid-19 vaccines have shown remarkable efficacy with developers showing that they were up to 95 per cent effective. These vaccines include one from US pharmaceutical giant Pfizer/BioNTech Covid-19 which was tested in well over 43,000 people and shown to be safe and effective. Another US company Moderna also developed a Covid-19 vaccine with efficacy around 94 per cent. Both vaccines are now awaiting approval from the FDA. Some other Covid-19 vaccines like the Oxford University and Novavax vaccines are also promising but not as effective as the two mentioned above. China and Russia have also developed and approved Covid-19 vaccines which are already being rolled out for clinical use within their respective countries but much is still to be known about them.
Who is supposed to receive the vaccine against Covid-19 and who is not supposed to receive?
The safety of these vaccines has been proven through vigorous tests in animals and humans. 
Virtually everybody will be eligible for Covid-19 vaccination once the WHO Okays a suitable vaccine for global use. 
From what moment is the Covid-19 vaccine effective to a human being after administration?
This is still being determined but for most vaccines people are protected within the first two weeks of receiving the last dose of the vaccine. Also, after receiving the Covid-19 vaccine, the duration for a person to be immune against the virus is yet to be determined. The vaccine is still being rolled out.
Why is it that each country has its own vaccine ag...