U.S. heads into Labor Day with Covid vaccines but a substantially worse outbreak than this time last year

The viral load in the nasal cavity is so high, estimated at 1,000 times that of other strains, that scientists in Australia say they traced a case where a man contracted it with just 5 to 10 seconds of exposure. The small fraction of fully vaccinated people who get Covid, even an asymptomatic case, are just as capable of spreading it as unvaccinated people, officials have warned. The delta variant now accounts for 99% of all new sequenced cases in the U.S.

“The delta variant, as we’ve seen with the evolution of Covid-19 over the past year and a half, continues to throw us curves, and I think the best advice is to be cautious and careful,” Dr. Nusheen Ameenuddin, a community pediatrician at the Mayo Clinic, said in an interview.

The good news is that delta appears to be running its course in the U.S., running out of new people to infect as vaccination rates rise and others gain natural immunity after recovering from the virus, doctors and scientists say.

New hospital admissions have finally started to turn after weeks of a steady rise, with the seven-day average of daily admissions down 1.7% over the past week, CDC data shows. Still, more than 100,000 Americans are currently hospitalized, compared with about 41,000 during the same week a year ago, according to the Department of Health and Human Services, in line with levels seen in late January of this year.

The big question is: How long does immunity last? Studies show that the vaccines start to wane in effectiveness about two months after the second shot and then really decline in protection five to eight months following full vaccination, U.S. officials say.

“We may see periodic waves of this until there is sufficient community-level protection, and hopefully that comes via vaccination rather than recovery from natural infection,” said infectious diseases physician Dr. Isaac Bogoch at the University of Toronto. “I know we all want the pandemic to be over, but it’s not. We are closer to the end in countries with access to vaccinations, but it’s not over.”