By Nancy Lapid

Aug 18 (Reuters) - Here is a summary of some recent studies on COVID-19. They include research that warrants further study to corroborate the findings and that have yet to be certified by peer review.

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 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 U.S. Centers for Disease Control and Prevention (CDC) announced on Wednesday that COVID-19 booster shots https://www.reuters.com/world/us/us-start-offering-covid-19-vaccine-booster-doses-september-2021-08-18 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% in late June to early August, from 74.7% before Delta became predominant, according to a study https://bit.ly/3mebUYT of U.S. long-term care facilities https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e3.htm.

- Vaccine efficacy for preventing new infections dropped from 91.7% to 79.8% between early May and late July, though efficacy at preventing hospitalization remained above 90%, according to a study by New York State health officials https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e1.htm.

- Protection from hospitalization lasts at least six months, according to a study in 18 U.S. states https://www.cdc.gov/mmwr/volumes/70/wr/mm7034e2.htm. It found that 24 weeks after full vaccination with an mRNA vaccine, efficacy was 84%, and it was 90% 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 https://go.nature.com/3xSRvLf. 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."

Click for a Reuters graphic https://tmsnrt.rs/3c7R3Bl on vaccines in development.

(Reporting by Nancy Lapid; Editing by Tiffany Wu)