Negative VE and rVE against severe COVID-19 outcomes
Several studies reported that COVID-19 vaccine effectiveness (VE) and relative vaccine effectiveness (rVE) against severe COVID-19 outcomes can turn negative after a few months.
One recently published paper (data analyzed were from 8 December 2020 to 30 June 2021) concludes that For Doses 1 and 2 of ChAdOx1 and Dose 1 of BNT162b2, VE/rVE reached zero by approximately Days 60–80 and then went negative. By Day 70, VE/rVE was –25% (95% CI: –80 to 14) and 10% (95% CI: –32 to 39) for Doses 1 and 2 of ChAdOx1 (see Figure). The same trend was observed for BNT162b2 although it seemed to provide a better protection.
Another not-yet published paper found that vaccine effectiveness was waning for all studied doses, including the 4th booster that worked for 90 days. Among health-care workers who had not had previous SARS-CoV-2 infection, time-specific vaccine effectiveness decreased from 52% (95% CI, 45 to 58) during the first 5 weeks after vaccination to −2% (95% CI, −27 to 17) at 15 to 26 weeks.
Vaccine effectiveness for children was negligible or negative 3 months or more after vaccination (−1.7%; 95% CI, −16.9 to 11.5 among those who had completed their primary series between February 1, 2021, and June 30, 2021, according to this Qatar study)
According to a study from Netherlands, during the Omicron-period, vaccine effectiveness against infection (VE-infection) was -36% (95% CI: -88%-1%) for primary series and -30% (95% CI: -80%-6%) for booster vaccination. It was positive for infectiousness though - indicating that vaccinated people may be less likely to pass the virus to each other.