- The COVID-19 vaccine effectively prevents severe illness and death.
- The Delta (B.1.617.2) variant of SARS-CoV-2 is spreading globally in populations with high vaccination rates.
- 1 in 4 fully vaccinated people who have exposure to the Delta variant in the home are likely to get the infection.
- The peak viral load of the Delta virus does not differ between fully vaccinated and nonvaccinated individuals.
- The elimination of the Delta strain of the virus takes place more quickly in vaccinated individuals.
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The SARS-CoV-2
Several studies have shown the effectiveness of the COVID-19 vaccines in protecting from severe disease and death. Research has also confirmed that fully vaccinated individuals have a lower risk of infection with both the
However, to date, vaccination has not limited the spread of the Delta variant. A new study, which appears in
Researchers from Imperial College London, the UK Health Security Agency, and the Manchester Foundation NHS Trust collaborated to carry out this “real life” study of household transmission in the U.K.
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The researchers recruited 621 people over 12 months from Sept 2020. Of these individuals, 163 (26%) had a SARS-CoV-2 infection. The team used genome sequencing to identify the variant:
- 71 participants had a Delta variant infection
- 42 had an Alpha variant infection
- 50 had a pre-Alpha variant infection
The scientists used the
Dr. Simon Clarke, who is an associate professor in cellular microbiology at the University of Reading and was not involved in the study, says:
“These findings show that the vaccines remain an effective way to drive down [SARS-CoV-2] infection, but they are not a silver bullet. Infection in the wider community can still be amplified by transmission at home.”
The ability of the vaccine to prevent infection with the Delta variant in the household was roughly 34%.
Interestingly, the study found vaccination status to have no effect on the maximum amount of the SARS-CoV-2 Delta virus present, known as the peak viral load. Other studies have found similar viral loads in nasal swabs, irrespective of vaccine status.
“These similar peak viral loads in vaccine breakthrough infections may explain why infected vaccinated people were just as likely to pass on infection as infected unvaccinated people,” says Prof. Peter Openshaw, professor of experimental medicine at Imperial College London.
Despite no difference in viral load, the body reduced the amount of SARS-CoV-2 Delta in the airways more quickly in vaccinated people than in unvaccinated people.
Speaking with Medical News Today, Dr. Sarah Pitt, principal lecturer at the School of Applied Sciences, University of Brighton, explained: “What is interesting about this study is because they followed people up for 3 weeks, they could see how much virus they were shedding and for how long […]. This could be a useful finding, as it might provide new information about how long people should self-isolate for once they have tested positive.”
The researchers noted that the time between the completion of vaccination and study recruitment was longer for PCR-positive contacts than for PCR-negative contacts. This is an important finding according to Prof. Penny Ward, independent pharmaceutical physician, visiting professor in pharmaceutical medicine at King’s College London.
She says that this may indicate that “waning individual protection may occur from 3 months rather than the 6 months currently scheduled for booster doses.”
The researchers note that they only included the contacts of symptomatic individuals in this study. Despite each of these people being the first member of their household to have a PCR-positive test, it is possible that another household member may already have had the infection.
According to Professor Emeritus Keith Neal of the University of Nottingham, this study helps with “understanding why Delta is now the predominant variant worldwide. Delta is able to spread between vaccinated people in a way previous variants did not.”
The research shows that the Delta variant of the SARS-CoV-2 virus can transmit from fully vaccinated people, who can have similar amounts of it in their airways as someone who is unvaccinated.
However, the amount of the virus in the airways of a fully vaccinated individual clears more quickly, suggesting that the risk of transmission lasts for less time than it would if they were not vaccinated.
Dr. Clarke says: “[T]he fact that a vaccine reduces someone’s chance of getting [the infection] in the first place means that while the vaccines don’t provide complete protection against transmission, they are not completely ineffective.”
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