Sumary of Booster Shots and Declining Effectiveness of COVID-19 Vaccines: What to Know:
- Luis Velasco/StocksyResearchers say the effectiveness of COVID-19 vaccines does decrease over time, although it’s not certain yet if age is a factor.
- However, the University of California San Diego researchers wrote in the New England Journal of Medicine last week that mRNA vaccine effectiveness against symptomatic COVID-19 cases had dipped to 65 percent by July 2021, with the drop-off attributed to waning effectiveness over time.
- “The decline in effectiveness is not entirely surprising,” said Dr. Francesca Torriani, professor of clinical medicine in the division of infectious diseases and global public health at the UC San Diego School of Medicine, as well as a program director of infection prevention and clinical epidemiology at UC San Diego Health.
- “Clinical trial data suggested decreased effectiveness would occur several months after full vaccination, but our findings indicate that confronted by the Delta variant, vaccine effectiveness for mildly symptomatic disease was considerably lower and waned 6 to 8 months after completing vaccination,” Torriani explained.
- Watanabe, PharmD, PhD, a COVID-19 health outcomes researcher and associate dean of assessment and quality at the University of California Irvine, told Healthline that research shows that the effectiveness of mRNA vaccines seems to decline about 6 percent every 2 months.
- “We found that 7–13 days after the booster shot there is a 48–68 percent reduction in the odds of testing positive for SARS-CoV-2 infection, and that 14–20 days after the booster the marginal effectiveness increases to 70–84 percent,” the researchers from Maccabi Healthcare Services reported.
- Studies on vaccine waning have been inconclusive about whether or not protection weakens more rapidly among people over age 65.The study from Israel suggested that effectiveness among older adults declined more than among other age groups.