Yes, vaccines are in short supply in most of countries right now but sooner or later that will end. And when it will end, countries where people will vaccine will have 70% population vaccinated (since kids can not be vaccinated that mean that there has to be 85%+ adults vaccinated to reach 70%). Others countries with have 50% or 40% people vaccinated. And that will be to little to prevent further spreading of covid. Those countries will suffer most on long term.
The US has currently approved vaccinating those in the 12 to 18 age group, so the coverage can be over 70%. And for those below 12 years, trials are ongoing and I guess these groups also will be allowed for vaccination soon. But the main issue here is the availability of vaccines. Pfizer and Moderna are making billions of USD in profits, while people are dying in poor countries. Only very recently, the American regime reacted positively to the suggestion of waiving IP for the COVID 19 vaccines. But I don't know when that is going to happen, as the pharma giants are opposing this move.