Vaccines' efficacy against infection weakens
The Covid-19 vaccines available in the United States are still highly effective at preventing hospitalization but their effectiveness against new infections has decreased as the Delta variant spread, according to new studies published on Wednesday (Aug 18) in Morbidity and Mortality Weekly Report.
None of the studies could tell whether the breakthrough infections were due to waning immunity, reduced protection against the Delta variant, or a combination of factors.
Still, the US Centres for Disease Control and Prevention (CDC) announced on Wednesday that Covid-19 booster shots would be made available to all Americans beginning in September. The new studies found:
- Vaccine effectiveness against any SARS-CoV-2 infection - mild or severe - dropped to 53.1 per cent in late June to early August, from 74.7 per cent before Delta became predominant, according to a study of US long-term care facilities.
- Vaccine efficacy for preventing new infections dropped from 91.7 per cent to 79.8 per cent between early May and late July, though efficacy at preventing hospitalization remained above 90 per cent, according to a study by New York State health officials.
- Protection from hospitalization lasts at least six months, according to a study in 18 US states. It found that 24 weeks after full vaccination with an mRNA vaccine, efficacy was 84 per cent, and it was 90 per cent among adults without immunocompromising conditions.
Children's noses are "pre-activated" to fight the virus
Children's noses may be better than adults' at defending against infection because of "pre-activated" immunity against the coronavirus, a new study suggests.
Researchers analyzed nasal swabs from 45 infected patients, including 24 children, and from 42 healthy individuals, including 18 children.
In nasal-lining cells and immune cells from the children's swab samples, they saw higher levels of genetic material that can sense the presence of the virus and trigger the immune system to defend against it.
Higher amounts of these sensors result in stronger early immune responses in children than in adults, according to a report published on Wednesday in Nature Biotechnology.
The nasal samples from the children were also more likely than adult samples to contain immune cells known as T cells that play roles in fighting infection and in developing long-lasting immunity, the researchers found.
Ultimately, the authors concluded, the effects may lead to a reduction in the ability of the virus to reproduce and help children to clear it from the body faster.
"In fact," they added, "several studies already showed that children are much quicker in eliminating SARS-CoV-2 compared to adults, consistent with the concept that they shut down viral replication earlier."