It’s unclear how long the vaccine by Pfizer and BioNTech will protect against coronavirus infection because the vaccine has been studied for only a few months.
The average age of people with Covid-19 is now much younger and people infected with coronavirus may have been less exposed to the virus because of social distancing and face mask wearing.
Experts say that children will also have to wait for the Covid-19 vaccine as most clinical trials for candidate vaccines have not included children as their subjects.
Both Eli Lilly and the National Institutes of Health referred to a potential safety issue, which appeared to indicate that the difference between the trial groups was due to a possible side effect.