Peak viral load therefore now appears similar in infected vaccinated and unvaccinated individuals, with potential implications for onward transmission risk, given the strong association between peak Ct and infectivity34. However, the degree to which this might translate into new infections is unclear; a greater percentage of virus may be non-viable in those vaccinated, and/or their viral loads may also decline faster as suggested by a recent study of patients hospitalised with Delta31 (supported by associations between higher Ct and higher antibody levels here and in35), leading to shorter periods “at risk” for onwards transmission. Nevertheless, there may be implications for any policies that assume a low risk of onward transmission from vaccinated individuals (e.g. relating to self-isolation, travel), despite vaccines both still protecting against infection, thereby still reducing transmission overall. This may be particularly important when vaccinated individuals are not aware of their infection status or perceive that their risk of transmission is low. Importantly, those infected after second vaccination appeared to gain an antibody boost, and higher prior antibody levels were independently associated with lower viral burden.