In the U.S., new data published by the Centers for Disease Control and Prevention (CDC) showed around a quarter of coronavirus infections among Los Angeles County residents were among fully vaccinated individuals between May and late July — a period in which the highly contagious delta variant was circulating.
Those without shots are still significantly more vulnerable, though. Ontario public health data found unvaccinated individuals were about eight times more likely to contract COVID-19 in the past 30 days.
Recent cases in British Columbia showed a 10-times higher rate of infection among unvaccinated people and a 17-times higher hospitalization rate.
A U.K. study from July suggested vaccine effectiveness dipped against delta compared to the alpha variant, offering between 67 and 88 per cent protection against infection.
Some fully vaccinated people have either required hospitalization or intensive care or died following a breakthrough infection.
"In long-term care and in the vulnerable, yes, they're reaching waning immunity, but they never have immune responses that last as long."
Recent data from the United Kingdom showed that some fully vaccinated COVID-19 patients had similar viral loads to unvaccinated people who contracted the virus.
That would seem to suggest vaccinated people are just as contagious.
Bogoch said the best way to halt spread among both vaccinated and unvaccinated groups is to continue with added layers of protection, including mask-wearing and limits on indoor gatherings, to "stop infections in the community."