Experts who have studied UK household cases have revealed that those who have been double vaccinated are catching COVID-19 and passing it onto those they live with.
The chances of double jabbed people transmitting the virus to other unvaccinated housemates is approximately two in five, or 38%. However, this drops to one in four, or 25%, if the housemates are also fully vaccinated. This emphasises the importance of full vaccination and protection against the virus.
Whilst vaccines have demonstrated efficacy in protecting people against severe COVID-19 illness and deaths, they are less effective at preventing infections. This is due to the emergence of new variants across the UK, particularly the dominant and highly infectious Delta variant.
As most COVID-19 transmission occurs within households, experts say that it is vital to ensure that every member who is eligible for a vaccine has received one, and is up to date with their doses.
Speaking to the BBC, Prof Ajit Lalvani, of Imperial College London, UK, who co-led the study, said: "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.
"We found that susceptibility to infection increased already within a few months after the second vaccine dose - so those eligible for booster shots should get them promptly."
Booster jabs are currently being rolled out to the elderly and immunocompromised, via the NHS, to prepare for a winter surge in COVID-19 cases. The Pfizer, Moderna, and AstraZeneca vaccines have all been approved for use as booster jabs by the MHRA.