Pfizer said in a statement that there is “no data” to show that a single dose of its coronavirus vaccine protects against infection after 21 days.
Why it matters: The UK announced on Wednesday that it would change its vaccination strategy “to give as many people in high-risk groups their first dose as possible, rather than giving the required two doses in the shortest amount of time”. Some provinces in Canada do the same.
- In response, Pfizer confirmed that although some protection appears to begin as early as 12 days after the first dose, two doses of the vaccine – separated by three weeks – is the only regimen that has been shown to be 95% effective in phase 3 studies.
- “Everyone is still getting their second dose and this will be within 12 weeks of their first,” the UK government added in a statement. “The second dose completes the course and is important for longer term protection.”
The big picture: Pfizer’s warning comes because many countries, including the US, are discussing how to use the vaccines quickly and in the most effective way. The US is on track to fall well below its target of vaccinating 20 million people by the end of 2020, with just 3 million single doses delivered as of Wednesday evening.