Vaccine Effectiveness Drops to Minus-75% in 18-29 Years-Olds as Omicron Slices Through Vaccine Protection and Booster Effect Starts to Wear Off

The latest Vaccine Surveillance report from the UKHSA shows a sharp drop in unadjusted vaccine effectiveness against infection (calculated from the raw infection rate data) in 18-29 year-olds, down to minus-75% in the month ending December 19th, from minus-10% the previous week.

Unadjusted vaccine effectiveness fell in all age groups this week, particularly sharply in 30-39 year-olds, where it hit minus-98%. In 40-49 year-olds it fell to minus-131%. Negative vaccine effectiveness means the vaccinated are more likely to be infected than the unvaccinated. A vaccine effectiveness of minus-100% means the vaccinated are twice as likely to be infected as the unvaccinated.

With Omicron infections particularly prevalent in the young and the vaccinated, this drop is likely to be the impact of Omicron, combined with a waning of vaccine efficacy. The high relative rates of infection in the vaccinated compared to the unvaccinated undermine any argument for vaccine passports or mandates that depend on the idea that the vaccinated are less likely to be infected or pass on the virus. If anything, it’s the vaccinated who are a higher transmission risk to the unvaccinated rather than vice-versa.

Unadjusted vaccine effectiveness against hospitalisation and death continues to hold up at a high level on this data, and increase in line with what is presumably a booster effect – though a drop in vaccine effectiveness against hospitalisation in 18-29 year-olds this week may portend a coming shift.