Thread by @celinegounder

1/ New @NEJM paper from Qatar on Pfizer vaccine effectiveness vs SARS-CoV-2 infection, severe COVID, or death from COVID.

nejm.org/doi/full/10.10…

2/ The study population included Qatar *residents*.

Note that 90% of people in Qatar are economic migrants from South Asia and other countries.

🤔

3/ Vaccine effectiveness vs INFECTION:
- Peaks at 78% ~1 month after 2nd dose of Pfizer vaccine
- Declines over time

4/ Vaccine effectiveness vs HOSPITALIZATION & DEATH:
- Remains high out to 6 months
- Appears to drop at 7+ months after 2nd dose of Pfizer vaccine

5/ Note that the median age of the study participants was 31 years. So this wasn't an especially old group.

6/ The dominant SARS-CoV-2 variant in Qatar during the study period was mostly Beta, but Delta became dominant later in the study period.

7/ Vaccine effectiveness vs SYMPTOMATIC infection was HIGHER than vs ASYMPTOMATIC infection.

8/ Vaccine effectiveness numbers in Qatar may appear lower than elsewhere because they test ~5% of the population every week.

9/ As in the U.S. & Israel, 2nd doses of Pfizer were given 3 weeks after 1st dose.

This is in contrast to the UK, EU countries, and Canada, where doses were spaced farther apart.

10/ In summary:
- Vaccine effectiveness vs INFECTION drops over time
- Vaccine effectiveness vs HOSPITALIZATION & DEATH remains stable out to 6 months
- There *may* be a drop at 7+ months, but the confidence intervals are SUPER WIDE. We need more data.