Timing of fourth dose
By March of this year, 86.2% of the U.K. population aged over 12 years had received at least two doses, but with rises in disease prevalence and the spread of variants of concern, further work is ongoing to understand the waning of the immune response, level of protection, and why some individuals develop COVID-19 even when double-vaccinated.
This news organization asked Susanna Dunachie, BMChB, professor of infectious diseases, University of Oxford, U.K., what the interval findings might mean for the timing of the fourth dose of vaccine across the U.K. population.
In the United Kingdom, fourth doses are being given to people who are 75 years and older, residents in care homes for older people, and those with weakened immune systems. “To make decisions about fourth doses for healthy people, we need to see how quickly antibody and T-cell responses drop,” said Ms. Dunachie, who is part of the large SIREN study team but was not involved in the analysis led by Dr. Otter. “Current research suggests that the T-cell response may be better maintained than the antibody response, and less affected by variants like Omicron.”
She explained the balance between antibody and T-cell responses to vaccination. “It is likely that antibodies that neutralize the virus are important for preventing any infection at all, and these unfortunately do fall in time, but T-cell responses are better sustained and help keep people out of [the] hospital,” she said.
Ms. Dunachie added that it was necessary to wait and observe what happens next with SARS-CoV-2 evolution, as well as wait for longer follow-up after the third dose in healthy people. “On current evidence, my estimate is we postpone decisions on fourth doses in healthy people to late summer/autumn.”
A version of this article first appeared on Medscape.com.