People vaccinated against Covid-19 are equally as infectious as the unvaccinated, according to new research.
The new study, published inand one of the few to date to use detailed infection data from actual household transmission, suggests the peak viral load for both vaccinated and unvaccinated people who are positive for the coronavirus is broadly similar.
The research involved 621 people in the UK with mild Covid infections and found people who had received two doses of a vaccine can nevertheless pass that infection on to both vaccinated and unvaccinated fellow household members.
While infections in vaccinated people cleared more quickly, their viral load, the degree of infectiousness for both cohorts was similar.
The study did find that vaccinated household contacts are less likely to suffer a breakthrough infection compared with their unvaccinated counterparts, although not to a massive extent – some 25% of vaccinated household members subsequently tested positive for the virus following close contact with a confirmed case compared with 38% for the unvaccinated cohort.
Those figures would appear to confirm Delta has a greater capability for breaching a vaccine’s defences compared with its predecessors, although it is no more effective at causing serious illness among the vaccinated.
“Our findings show that vaccination alone is not enough to prevent people from being infected with the Delta variant and spreading it in household settings,” said Professor Ajit Lalvani of Imperial College London, the co-leader of the study.
“The ongoing transmission we are seeing between vaccinated people makes it essential for unvaccinated people to get vaccinated to protect themselves from acquiring infection and severe Covid-19, especially as more people will be spending time inside in close proximity during the winter months,” he said.
Professor Lalvani also said the study’s results have underlined the importance of booster shots for those whose vaccine immunity has begun to wane with time, with the median length of time since vaccination for those who were infected being 37 days longer than for those who resisted the infection.
“We found that susceptibility to infection increased already within a few months after the second vaccine dose – so those eligible for Covid-19 booster shots should get them promptly,” he said.
The study identified its 621 participants, all of whom had either a mild infection or were asymptomatic, via the UK’s contact tracing system between September 2020 and September 2021.