Gretchen VogelScience’s COVID-19 reporting is supported by the Heising-Simons Foundation.Faced with short supplies of COVID-19 vaccines and unforeseen side effects, some countries have adopted an unproven strategy: switching shots midstream.
Most authorized vaccines require two doses administered weeks or months apart, but Canada and several European countries are now recommending a different vaccine for the second dose in some patients.
Early data suggest the approach, born of necessity, may actually be beneficial.In three recent studies, researchers have found that following one dose of the vaccine made by AstraZeneca with a dose of the Pfizer-BioNTech vaccine produces strong immune responses, as measured by blood tests.