About one in three (34% of 110 vaccinees) who received a first AstraZeneca dose followed by a Pfizer dose experienced a fever, versus 10% of 112 recipients who were given two doses of the AstraZeneca vaccine (difference, 14 percentage points). The groups receiving two different vaccines had more systemic reactions after the second dose than after the first, the most common of which was fever. In the 28-day group, the researchers found more short-term adverse effects after two doses of different vaccines given in either order than after two doses of the same vaccine, but they identified no other safety issues. Mean participant age was 57 years, 46% were women, and 25% were of minority races. (Those in the 84-day group have not completed the study yet.) Some groups were given two doses of the same vaccine (homologous group), while the others received doses of both the Pfizer and AstraZeneca vaccines in either order (heterologous group).Īll participants in the 28-day group had received their first dose, and all but two had received their second. Of the participants, 463 were randomly assigned to one of four groups receiving a second vaccine dose at 28 days, and 367 were randomly assigned to receive a second dose at 84 days. The study recruited from Feb 11 to 26, 2021. All participants had either no or mild to moderate underlying illnesses in the 7 days after their first and second doses of the vaccines. The preliminary research, out of the Com-COV study of vaccine second doses led by University of Oxford researchers, involved 830 vaccine recipients from eight sites. The European Union, for example, recently announced that it would not renew its contract with AstraZeneca beyond June and had signed a new contract with Pfizer. The descriptive findings could help inform countries' decisions about how to proceed with second doses after suspending or stopping orders of the AstraZeneca vaccine amid reports of rare but serious blood clots, the authors noted. Adults 50 and older who received doses of both the Pfizer/BioNTech and AstraZeneca/Oxford COVID-19 vaccines reported more mild and moderate side effects than those given only one type of two-dose vaccine, according to a study yesterday in The Lancet.
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