Full vaccination significantly changes your chances of spreading the SARS-CoV-2 virus.
Being fully vaccinated against COVID-19 means you are significantly less likely to get seriously ill or die from COVID-19 infection, compared to unvaccinated people. Now, new evidence is showing that vaccination will also protect everyone around you – by greatly reducing levels of transmission.
According to Dr Christopher Byron Brooke at the University of Illinois at Urbana-Champaign, in the USA, vaccines are not a perfect protection, but they greatly reduce transmission risk. “Vaccinated people do transmit the virus in some cases, but the data are super crystal-clear that the risk of transmission for a vaccinated individual is much, much lower than for an unvaccinated individual,” Dr Brooke said in a recent news release.
What studies are saying
One report, led by Public Health England, analysed transmission levels among 365,000 households with a mix of vaccinated and unvaccinated members. The report found that vaccination with either the Pfizer or AstraZeneca vaccine reduced the chance of transmission by 40 – 60%. In plain words this means that if someone who was vaccinated became infected, they were less than half as likely to transmit the virus to others, compared to people who were unvaccinated.
Another study, led by Dutch researchers, found that vaccines have 71% effectiveness against transmission. The study looked at data from the Netherlands from February to May, when the Alpha variant (B117) was dominant and the available vaccines were by Pfizer, AstraZeneca, Moderna, and Johnson & Johnson. Among 113,582 adult index cases (the first case found within a household or group) and 253,168 close contacts of all ages, the study found that transmission of the virus, measured as secondary attack rate, fell from 31% to 11% if the index patient was fully vaccinated.
Finally, a study that investigated breakthrough infections in thousands of partially and fully vaccinated individuals, found that vaccination greatly reduced the chance of infection – just 0.2% of those fully vaccinated became infected with the virus. “Between Dec 8, 2020, and July 4, 2021, 1,240,009 COVID Symptom Study app users reported a first vaccine dose, of whom 6,030 (0.5%) subsequently tested positive for SARS-CoV-2 (cases 1), and 971,504 reported a second dose, of whom 2,370 (0.2%) subsequently tested positive for SARS-CoV-2 (cases 2).
These findings show the importance of full vaccination to reduce the spread of the virus. According to Dr Jennifer Juno, Senior research fellow at The Peter Doherty Institute for Infection and Immunity and Dr Adam Wheatley, Senior Research Fellow from the Department of Microbiology and Immunology at The University of Melbourne, current data show that while highly efficient at reducing the risk of transmission, vaccines are not perfect, and preventive behaviours, such as social distancing, lockdowns and wearing masks, should continue to be implemented.
“While vaccinated individuals most likely have a smaller chance of passing on the virus, it’s still important to keep up responsible behaviours into the immediate future to protect those who have not, will not, or cannot be immunised,” these researchers wrote in a recent report.