Coronavirus: vaccinated households still at risk of transmission Delta
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TORONTO – Fully vaccinated people who experience breakthrough infections of the highly transmissible and globally dominant Delta variant can still transmit the virus to vaccinated household members, although at lower rates than those who are not vaccinated. suggests a new British study.
The latest findings published in The Lancet Infectious Diseases this week show that although COVID-19 vaccines reduce the risk of infection, there is still a 25 percent chance, or one in four, of catching the Delta d variant. ‘a vaccinated person living in the same household. The risk of transmission to an unvaccinated household member is close to 40%.
Experts told CTVNews.ca that as vaccination rates increase, the number of breakthrough cases will also increase, simply because there are fewer unvaccinated people. Additionally, many cases of breakthrough are asymptomatic and would otherwise go unnoticed. But the rate of hospitalizations and deaths remains considerably higher among unvaccinated people than among those who received both vaccines.
Previous studies have already established that vaccines help prevent serious illness and death, but research suggests they may be less effective against the Delta variant.
A major UK study published in August that looked at the effectiveness of Pfizer-BioNTech and AstraZeneca injections, the vaccines included in The Lancet study, showed that they remained 88 percent effective against the Delta variant with Pfizer (vs. nearly 94 percent). percent with the Alpha variant) and 67 percent (vs. 74.5 percent) with the AstraZeneca version. Studies have also shown that while their effectiveness against hospitalizations caused by Delta has also decreased, they have remained high overall.
The Lacet study, led by Imperial College London and the UK Health Security Agency, also showed that while fully vaccinated individuals recover from infection faster than those who received no injections, the amount of SARS-CoV-2 viruses found in both groups were similar at their peaks. This could explain why vaccinated people can still transmit the virus up close, the researchers said.
“Vaccines are essential in controlling the pandemic … However, our results show that vaccination alone is not enough to prevent people from becoming infected with the delta variant and spreading it in households,” said the co-author Ajit Lalvani, professor with Imperial College London, in a statement.
“The continued transmission we see between people who have been vaccinated makes it essential for unvaccinated people to get vaccinated to protect themselves against infection and severe COVID-19, especially as more and more people will spend time indoors nearby during the winter months. “
Domestic transmission is known to be a dominant source of the spread of infection, but the Lancet study is one of the few to date that sheds light on the Delta variant and how vaccinated people who are asymptomatic or only mildly ill people can still contract and transmit the virus.
The study recruited 621 people between September 2020 and September 2021 for two studies, one on the Alpha variant and pre-Alpha cases, and the other on the Delta. Participants were swabbed daily for up to 20 days, providing a total of 8,145 upper respiratory tract samples.
Seventy-one participants had the Delta variant and were mildly ill or had no symptoms. Scientists followed 205 household contacts for the Delta cohort through daily polymerase chain reaction (PCR) tests. Sixty-two percent, or 126 contacts, were fully vaccinated, 19 percent, or 39 people, had received a dose, and 19 percent, or 40 people, had not been vaccinated.
Ultimately, 31 of 126 fully vaccinated household contacts, or 25%, were infected with the Delta variant, while 15 of 40 unvaccinated contacts, or 38%, were infected. The median time since vaccination for those infected was 101 days. For uninfected contacts, it was 64 days, suggesting waning protection and an increased risk of infection after about three months, the researchers said, results that strengthen the evidence that booster injections will be needed.
“This finding is consistent with the known protective effect of COVID-19 vaccination against infection. Nonetheless, these results indicate a continued risk of infection in household contacts despite vaccination, ”the authors wrote in the article, noting that their results on secondary attack rate were higher than studies conducted before the emergence of the Delta variant.
PCR tests also measured the amount of virus present, called the viral load, in the samples. The results revealed that the viral load decreased most rapidly in those who were vaccinated compared to those who were not, findings that are in line with other studies. However, at its peak, the amount of virus present in vaccinated and unvaccinated individuals was comparable.
“Our results provide important information about the effect of vaccination in the face of new variants, and more specifically, why the delta variant continues to cause a high number of COVID-19 cases globally, even in high-risk countries. high vaccination rates, ”lead author Dr Anika Singanayagam of Imperial College London said in a statement.
“The continuation of public health and social measures to curb transmission therefore remains important, even among vaccinated people. ”
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