a single dose of pfizer or moderna produced short-term antibody levels more than one-and-a-half times greater than those produced by astrazeneca. antibody levels in people with two doses of pfizer or moderna were almost twice as high as those after the first dose.
the early results don’t include people who received two doses of astrazeneca.
in quebec, people still need to wait eight weeks at least between doses, regardless of the vaccine.
in ontario, people must wait a minimum of eight weeks after a first dose of astrazeneca, but only a minimum of 28 days after a first dose of pfizer of moderna.
pfizer and moderna were formally authorized for use 21 and 28 days apart, respectively. but the choice of three weeks or four “wasn’t based on decades of vaccinology,” said mcmaster university immunologist dawn bowdish. “it was based on, what’s the minimal amount of time you can squish doses together to get everyone protected?”
“pilot data coming out says, yes, actually, if you wait a little longer between doses you get a little bit of a bump in your immune response,” bowdish said. in march, canada’s vaccine advisors said doses could be spaced up to four months apart. with growing vaccine supplies, and the delta variant spreading, the advisory panel now says second doses should be given as soon as possible.