After weeks of sharp declines, new Covid-19 cases are beginning to flatten

The 7-day average of daily new cases was just over 72,000 on Wednesday, according to data from Johns Hopkins University, a total that is relatively unchanged from last Thursday. Compare those numbers to the previous Thursday, February 11, when the US averaged about 102,000 new cases per day.

Experts say it is too soon to tell whether this one-week flattening represents a small blip or the beginning of a broader issue.

"I've been watching this and have been wondering the same thing," Dr. Ashish Jha, dean of the Brown University School of Public Health, told CNN on Thursday. "We have not seen widespread increases, but there is that flattening. We'll have to monitor this closely. The other thing we have to track is how the new variant is doing and whether that's part of the reason."

Getting infection numbers down now not only will help prevent the virus from further mutating but it will also give vaccines a better shot at remaining effective.

Meanwhile, new Covid-19 deaths and hospitalizations, which trail several weeks behind cases, have continued to sharply decline. And the two vaccines approved in the US have shown extraordinary success in limiting severe Covid-19, making the race to vaccinate so important.

Vaccines are already working in the real world

Both in the US and abroad, the vaccines are quickly proving their effectiveness.

A study of about 600,000 vaccinated people in Israel found that the Pfizer-BioNTech vaccine remains highly effective at preventing symptomatic coronavirus infections under real-world conditions.

The risk of symptomatic Covid-19 -- meaning people who were infected with the coronavirus and felt sick -- decreased by 94% among people who received two doses of the vaccine, according to the study. Even before the second dose, the vaccine's effectiveness approached 60%.

The vaccine cut the risk of severe disease by 92% and was highly effective across age groups, too. The vaccine also appeared to protect against a highly transmissible coronavirus variant first identified in the UK, researchers said.

Details of the study were first reported last week, but the full, peer-reviewed findings were published Wednesday in the New England Journal of Medicine. The results confirm that the vaccine remains remarkably effective outside the carefully controlled conditions of a clinical trial.

In addition, a New York Times analysis of federal data found that new cases and deaths have fallen significantly in nursing homes since vaccinations began in late December, outpacing the national declines.

Dr. Mark McClellan, director of the Duke-Margolis Center for Health Policy, described this as a "cratering" of hospitalizations and deaths in nursing homes.

"It is really going down to levels we haven't seen since before the initial big outbreaks in New York City," he said. "And that is incredibly good news and a reflection of just how important vaccination in those settings have been. Hopefully it is a sign of what is to come as we get more vaccination going faster now that the weather is better. Now that the number of vaccines and shots in arms is going up."

Concern on spreading variants

Still, experts have warned another case surge is likely on its way in the coming weeks, one that will this time be fueled by coronavirus variants -- and the country is still nowhere near herd immunity levels.

In fact, health officials are preparing for a possible third wave that will be driven by a rapidly spreading variant that was first identified in the UK: B.1.1.7. Data from the CDC shows more than 1,880 cases of the variant have been detected across the US -- but scientists have warned that number likely doesn't represent the total of cases in the country.

"We could all wish for this to be the last wave," said Andy Slavitt, the White House senior adviser for the Covid-19 Response Team. "But we wouldn't be doing our jobs if we weren't really focused on containment measures for variants, if we weren't really focused on how therapeutics might help to minimize the effects of the variants, how we might make sure, if we have another wave, it feels different," he told a webinar held by the American Public Health Association.

To address this growing threat, the CDC is collaborating with public and private labs to expand genomic sequencing capacity. And with the $200 million investment in sequencing from the Biden administration last week, the CDC hopes to quickly reach the goal of sequencing 25,000 sample sequences per week.

Meanwhile, two separate teams of researchers said they've found a worrying new variant in New York City and other areas in the Northeast that carries mutations helping it evade the body's natural immune response -- as well as the effects of monoclonal antibody treatments.

And two studies due to come out soon raise concerns about a variant that scientists have been keeping an eye on in California, hinting the variant might not only be more contagious, but may also cause more severe disease.

A third vaccine for US could be just days away

The US could be just days away from getting another vaccine on the market.

Vaccine advisers to the Food and Drug Administration will meet on Friday to determine if the Johnson & Johnson vaccine works and if it's safe. They will make a recommendation to the FDA and the agency could give the vaccine the green light as early as Friday or Saturday. Then, advisers to the CDC are scheduled to meet Sunday to discuss recommendations surrounding the vaccine's potential rollout -- recommendations that would have to be formally accepted by the CDC.

In an analysis released on Wednesday, the FDA said the Johnson & Johnson vaccine has met the requirements for an emergency use authorization.

The efficacy of the vaccine against moderate to severe/critical Covid-19 across all geographic areas was 66.9% at least 14 days after the single-dose vaccination and 66.1% at least 28 days after vaccination, according to the analysis.

"There were no specific safety concerns identified in subgroup analyses by age, race, ethnicity, medical comorbidities, or prior SARS-CoV-2 infection," the analysis said.

Meanwhile, the US supply of vaccines is set to ramp up significantly in the coming months.

Pfizer and Moderna -- whose vaccines were already authorized for emergency use -- have pledged to make a combined total of 220 million doses available for shipment by the end of March. Meanwhile, Johnson & Johnson, if it secures an emergency use authorization, has pledged to make 20 million doses available in the same time frame.

And a fourth Covid-19 vaccine could become available in the US in April -- which could add millions more doses to the country's supply by the end of that month.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told NBC's Savannah Guthrie that Americans should get whichever shot is available the soonest rather than wait for one over another.

"This is a race, Savannah, between the virus and getting vaccines into people. The longer someone waits on getting vaccinated, the better chance the virus has to get a variant or a mutation," he said. "So, the sooner we get vaccine into the arms of individuals, whatever that vaccine is, once it gets by the FDA for an EUA, if it's available to you, get it."

President Joe Biden has previously said the US will have enough vaccines for 300 million Americans by the end of July.