The human trials had already shown that just one dose of Pfizer has an efficacy of 89% after 15 days. With a fast-spreading pandemic, the priority is to get as many people on their first dose as possible. This both starts to reduce the rate of infection, and also reduces the death rate.
The long-term effectiveness isn't a priority at first for the most developed countries. If necessary they can just order more vaccine after a few months and run a booster campaign later in the year. Cost isn't an issue.
The human trials had already shown that just one dose of Pfizer has an efficacy of 89% after 15 days. With a fast-spreading pandemic, the priority is to get as many people on their first dose as possible. This both starts to reduce the rate of infection, and also reduces the death rate.
The long-term effectiveness isn't a priority at first for the most developed countries. If necessary they can just order more vaccine after a few months and run a booster campaign later in the year. Cost isn't an issue.