Severe obesity may weaken the effectiveness of COVID-19 vaccines in those who have never been infected with the coronavirus, according to a small Turkish study. Additionally, South African researchers have found infection with the Omicron variant of the coronavirus can significantly improve the immune system’s ability to protect against other variants, but only in people who have been vaccinated.

Although people who recover from COVID-19 usually gain some immune defenses against reinfection, they get additional protection from vaccines, especially against severe disease, according to two studies published on March 31 in The Lancet Infectious Diseases. Additionally, two gold-standard trials published in The New England Journal of Medicine on March 30 help settle questions about two controversial therapies touted by many early in the pandemic with decidedly mixed results – failure for the antiparasite drug ivermectin and success for antibody-rich blood plasma from COVID-19 survivors.

At least one model from the University of Washington’s Institute for Health Metrics and Evaluation estimates that at this time, 73 percent of Americans are immune to Omicron, and it could rise to 80 percent by mid-March.

The Omicron variant, which is spreading far faster than previous versions of the coronavirus, is not likely to help countries achieve so-called herd immunity against COVID-19 – in which enough people become immune to the virus that it can no longer spread – leading disease experts say.

U.S. President Joe Biden said on January 4 that COVID-19 cases were rising even at the White House as he urged unvaccinated Americans to get vaccinated and others to get booster shots.

The Omicron coronavirus variant is better at circumventing vaccinated peoples’ immunity than the Delta variant, according to a published Danish study, helping explain why Omicron is spreading more rapidly.

The U.S. Centers for Disease Control and Prevention issued a report that reviewed dozens of studies and the CDC’s own unpublished data on Covid-19 study concluding that immunity caused by natural Covid-19 infection and vaccines both lasted at least six months, but the immunity provided by the vaccines was more consistent.

Booster shots to bolster immunity against the coronavirus would be free and accessible, U.S. President Joe Biden said on Friday, one day after federal health agencies backed a booster rollout.

External advisors to the U.S. Food and Drug Administration will meet on Sept. 17 to consider data from Pfizer and BioNTech in support of booster shots. Meanwhile, a timeline is being presented on the authorization of Covid-19 vaccines for children.

U.S. Food and Drug Administration scientists said on Sept. 15 that booster doses of Pfizer’s Covid-19 vaccine may not be needed, even though the third shot generates a higher immune response in recipients.