How quickly do I need a second injection of COVID-19 vaccine?
The first COVID-19 vaccines in the United States require two doses a few weeks apart.
People should obtain some degree of protection within two weeks after the first injection, with the second injection providing full protection from the vaccine. For the vaccine from Pfizer and BioNTech in Germany, the second injection should be after three weeks. For Moderna, it’s four weeks.
But how strictly these guidelines must be followed has been a point of difference for the United States and the United Kingdom, which has been launching the Pfizer vaccine and one from Astrazeneca, which requires two doses administered four weeks apart.
To get more first shots at people and give them at least some degree of protection, the UK says it’s okay to delay reinforcements for up to 12 weeks. But that strategy has been rejected in the United States, where regulators say there is no science to support this approach.
A major concern is that it is not known how long partial dose protection can last. “There is no data to show that protection after the first dose is maintained after 21 days,” said Pfizer.
American regulators agreed, saying that very few people in the Pfizer and Moderna vaccine studies missed their scheduled reinforcements to have enough data to show that the strategy can work.
The timing of the shots does not have to be accurate in the United States; the Centers for Disease Control and Prevention say the second injection can be given up to four days before or after.
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