Pre-Omicron study found vaccines protected against severe illness for up to 6 months

Posted at 10:56 AM, Feb 22, 2022

BALTIMORE — A newly published research study from Johns Hopkins University and the World Health Organization found that COVID-19 vaccines remain pretty effective in protecting against severe symptoms up to six-months after two vaccination doses.

The research was conducted by analyzing pre-Omicron data between June 17 and December 2 last year.

The study did however show vaccine protection against symptomatic COVID patients —which includes both mild and severe illness—tapering off by an average of 24.9 percent (32 percent for older adults) from one month to six months post-vaccination.

"There is an indication here of waning vaccine effectiveness over time, though it is encouraging that protection from severe disease—the most worrisome outcome—seems to hold up well,” says study co-first author Melissa Higdon, MPH, a research associate in the Department of International Health and a member of the International Vaccine Access Center (IVAC) at the Bloomberg School.

How long vaccines protect from infection and severe disease is one of the most pressing questions still facing public health experts.

An analysis of post-vaccination infections with only the delta variant also found waning protection over time, suggesting that declining immunity—rather than changes in protection against the delta variant—was the principal reason for the waning vaccine effectiveness prior to the omicron wave.

“Omicron is still prevalent in many parts of the world, so it’s going to be critical for COVID-19-related policymakers to pay attention to vaccine effectiveness studies in the context of omicron as well as any future variants—and to assess effectiveness over extended periods of time after vaccination, including vaccination with booster doses,” Higdon says.