Pfizer said in a statement that there were no “data” to show that a single dose of its coronavirus vaccine would provide protection against the infection after 21 days.
Why does it matter: The UK announced on Wednesday that it would change its vaccination strategy “to give as many people in at-risk groups as possible their first dose, rather than the two doses needed in the shortest possible time”. Some provinces in Canada do the same.
- Pfizer confirmed in response, although some protection seems to start as early as 12 days after the first dose, two doses of vaccine – three weeks apart – are the only regimen that has been shown to be 95% effective in phase 3 studies.
- “Everyone will continue to receive the second dose and it will be within 12 weeks of their first,” the British government said in a statement. The second dose completes the course and is important for longer term protection.
The whole picture: Pfizer’s warning comes as many countries, including the United States, are debating how to implement vaccines as quickly as possible. The US is on track to drop well below its target of vaccinating 20 million people by the end of 2020, with only 3 million single doses given as of Wednesday night.