Several countries have started to recommend a booster shot of COVID-19 vaccines to some groups of fully vaccinated people in light of new evidence that vaccine effectiveness may decline over time, according to public health agencies.
The World Health Organization has called on countries to wait until at least 10 percent of people in every country are vaccinated to provide booster shots to fully vaccinated people.
The Centers for Disease Control and Prevention say new studies indicate that the ability of COVID-19 vaccines to protect people from infection declines over time, although protection against severe illness remains strong. Research into the benefits of booster shots is ongoing and evolving, health experts say. The WHO has called for a moratorium on booster doses of COVID-19 vaccines until global vaccine access improves.
“Examining numerous cohorts through the end of July and early August, three points are now very clear,” CDC director Rochelle Walensky said at a White House COVID-19 news briefing Wednesday. “First, vaccine-induced protection against SARS-CoV-2 infection begins to decrease over time. Second, vaccine effectiveness against severe disease, hospitalization and death remains relatively high. And third, vaccine effectiveness is generally decreased against the delta variant.”
While many assume ‘that after a booster dose you will be more protected than prior to a booster dose,’ says Dan Barouch, a virologist at Beth Israel Deaconess Medical Center, it’s too soon to know. “That very well might be true,’ Barouch says, ‘but it still remains to be shown.”