SARS-CoV-2 immune response

• How effective is a first or second dose of COVID-19 vaccine at making antibodies against the COVID-19 virus?

In our study, a single dose of AstraZeneca or Pfizer vaccines led to high levels of antibodies against the COVID-19 virus in our participants. However, the level of antibodies varied by vaccine type, age, and other medical conditions, showing that other measures such as social distancing are still very important even after one dose of vaccine. A second dose of either vaccine resulted in high antibody levels across all groups.

Research paper: Spike-antibody responses to COVID-19 vaccination

• How long do antibodies against the COVID-19 virus last after a second dose of vaccine, do antibody levels predict risk of infection?

We measured antibody levels in almost 9000 study participants who had received two doses of AstraZeneca or Pfizer vaccine at 3 weeks after the second dose and 20 weeks after the second dose. Antibody levels dropped at the same rate for both vaccines, but the starting level was much higher for the Pfizer vaccine. We found those with lower antibody levels were at increased risk of infection. Those vaccinated with AstraZeneca reached these lower antibody levels sooner than those vaccinated with Pfizer (96 vs 257 days) and had increased risk of breakthrough infections.

Research Paper: Spike-antibody waning after second dose of BNT162b2 or ChAdOx1