Pfizer-BioNTechA recent study found that only 13.5% of recipients of the COVID-19 vaccine from Pfizer (NYSE:PFE) and BioNTech (NSDQ:BNTX) had systemic side effects after the first dose. That figure climbed to 22.0% after the second dose.

Conversely, just over one-third (33.7%) of recipients of the first dose of vaccine from AstraZeneca (LON:AZN) had systemic side effects, according to the study published in The Lancet.

Among those with a prior COVID-19 infection, however, systemic side effects were 2.9 times more common in recipients of the first Pfizer vaccine than those who were infection naive. For recipients of the first dose of the AstraZeneca vaccine, such side effects were 1.6 times more common in those previously infected with COVID-19.

The study, which involved 627,383 participants, ran from Dec. 8 to March 10.

Local side effects (frequently injection-site pain and tenderness) were more common than systemic events, occurring in 71.9% of recipients of the first dose of Pfizer vaccine and 68.5% of those receiving the second. A total of 58.7% of those receiving the first dose of the ChAdOx1 AstraZeneca vaccine had local side effects.

Prior exposure to COVID-19 did not appear to influence the rate of local side effects significantly.

The Pfizer vaccine yielded 69% protection against infection risk between 21 and 44 days after administering the first dose. That figure climbed to 72% between 45 and 59 days after the initial vaccination.

A single dose of the AstraZeneca vaccine offered 60% protection 12 days after the first dose.