Issue #117
September 2021
Are COVID-19 vaccines effective against transmission?

A recent study into vaccine effectiveness against SARS-CoV-2 transmission showed that COVID-19 vaccines* not only protect the vaccinee against infection, but also offer protection against transmission to close contacts[1]. Dr Michael Dray, President of the RCPA explains that this study highlights the importance of full vaccination of close contacts of vulnerable persons and encourages everyone to get vaccinated as soon as possible.

“We already know that COVID-19 vaccines are highly effective against SARS-CoV-2 infection, however what has not been clear is how effective the vaccines are against transmission. The good news is that there is mounting evidence to suggest that COVID-19 vaccines are likely to substantially reduce the chance of transmitting the virus to others. This ultimately means that every person who chooses to get vaccinated protects not only themselves, but also others around them from COVID-19.

“There have been over 25 million COVID-19 vaccine doses administered in Australia[2] so far and 4.7m in New Zealand[3], which shows we are moving in the right direction, but it is vital that we keep this momentum going. Vaccinations protect individuals, their families, friends and communities and to put it simply, will get us back doing all the things we love to do. At the moment, the greatest risk of transmission remains to be among the unvaccinated who are much more likely to get infected, and therefore transmit the virus to others. This study showed that vaccination greatly reduced transmission to close contacts,” said Dr Dray.

Using contact monitoring data in the Netherlands, the study looked into vaccine effectiveness against transmission (VET) of the Alpha variant to household and other close contacts. The study showed that the secondary attack rate among household contacts was lower for fully vaccinated than it was for unvaccinated index cases (11% vs 31%), with an adjusted VET of 71% (95% confidence interval: 63–77).

“Whilst this particular study focused on the Alpha variant, more real-life data is emerging which supports this claim for the Delta variant. What is absolutely clear is that vaccines are playing a crucial role in limiting spread of the virus and minimising severe disease. Whilst breakthrough infections do sometimes occur, fully vaccinated people are less likely to get COVID-19 than unvaccinated people, which will help to slow the spread of the virus. High vaccination coverage will reduce spread of the virus and help prevent new variants from emerging.

“Much is still unknown about this Delta variant and research into this area is still ongoing. We would remind people that even when vaccinated, it is important that they still continue to take the same precautions, such as avoiding crowds, keeping their distance from others and wearing masks. These are small easy steps that we know have been extremely effective throughout the pandemic and that still work against the Delta variant.

“In Australia and New Zealand, COVID-19 vaccines are free for everyone regardless of Medicare or visa status, so we encourage everyone to seek a vaccination as soon as possible. With new COVID-19 vaccine developments every day, it’s normal to have questions or concerns, and possibly feel hesitant about getting a vaccine. That's why it is important to seek accurate, evidence-based advice regarding COVID-19 vaccines,” said Dr Dray.

For more information on COVID-19 vaccines, visit: and in NZ visit:

*After completing the full schedule









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Find out more on the RCPA website
The Royal College of Pathologists of Australasia
Durham Hall - 207 Albion St Surry Hills NSW 2010 AUSTRALIA
Phone: +61 2 8356 5858