Ajit Lalvani, chair of infectious diseases at Imperial College London and lead author of the household-transmission study, said people in their 40s were at higher risk of breakthrough infection for two reasons. “Waning immunity plus pools of unvaccinated people acting as vectors of infection into the household where it transmits effectively to vaccinated parents,” he said. “Both are happening.”
Most people in their 40s received their second vaccination at least four months ago. ... They are also the most-likely age band to share a home with teenage children, a group that is still mostly unvaccinated in the U.K. and in which case numbers have been surging. The household-transmission study, which tracked 205 vaccinated and unvaccinated household contacts of a symptomatic case of Covid-19, found that around a quarter of those who were fully vaccinated went on to develop a breakthrough infection. The study, published in the medical journal Lancet Infectious Diseases last week, found that unvaccinated household members had a 38% chance of infection.
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