(CNN)Hope stemming from decreasing Covid-19 numbers has been blunted by the spread of new coronavirus variants.
Now, one of the most worrisome strains -- first found in South Africa -- has been detected for the first time in the US.
On Thursday, South Carolina officials confirmed two cases of the more contagious strain, also known as B.1.351.
Those two people, both adults, have no known travel history or connection to one another, state health officials said.
This strain has concerned scientists because it seems to more transmissible than other versions of the virus, and because it might evade some of the immune protection offered by antibodies.
Experts say they believe vaccines will still be effective against the variant, and the Centers for Disease Control and Prevention said "we have no evidence that infections by this variant cause more severe disease."
But this particular strain "troubles me," said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.
"When you look at the vaccines that we have available now, the neutralizing antibodies that they induce ... when you measure that against the South African isolate, it is diminished by multifold in its ability to cover it," Fauci told ABC's George Stephanopoulos on Thursday.
"It's still within the range of what you predict would be protective. But I take no great comfort in that."
And for anyone getting lax about safety precautions, the confirmation of the B.1.351 strain in the US should be a big wake-up call.
"The arrival of the SARS-CoV-2 variant in our state is an important reminder to all South Carolinians that the fight against this deadly virus is far from over," said Dr. Brannon Traxler, interim public health director for the state's health department.
The variant has been detected in more than 30 other countries, according to the World Health Organization.
The sobering news comes as health officials stress the need to wear masks, even after vaccination.
Why we're at a critical time
New variant strains spreading in the US could make even everyday activities more dangerous.
A highly contagious variant first spotted in the UK have been detected in at least 28 states, according to the CDC.
And Minnesota officials recently announced the first US case of another variant that was first detected in Brazil. That person had recently traveled from Brazil.
"The variants that have been identified recently seem to spread more easily," CDC Director Dr. Rochelle Walensky said.
"They're more transmissible, which can lead to increased number of cases and increased stress on our already overtaxed system."
With several days still left to go, January has already been the deadliest month of the entire pandemic in the US, with more than 80,000 deaths.
In less than one year, Covid-19 has claimed more than 430,000 US lives. And a composite forecast by the CDC projects another 84,000 deaths by February 20.
Why some vaccines are 'sitting on the shelves'
A total of 26,193,682 doses of Covid-19 vaccine have been administered, according to data published Thursday by the CDC. That's about about 54% of the 48,386,275 doses distributed.
Nearly 21.7 million people have received at least one dose of the vaccine and almost 4.3 million people have been fully vaccinated, CDC data shows.
The US is still grappling with vaccine allocation and distribution problems and it could be months until every American who wants a vaccine can get it.
During a CNN town hall Wednesday, Walensky explained some of the reasons why.
Some of the 48 million doses distributed just arrived in states, while others are still going through a dayslong distribution process to make it to their final destination, she said.
"So there is some delay from the time that they're distributed and to the time that they could possibly be administered," Walensky said. There's also a delay in reporting the administrations, she said.
"And then there are some doses that we need to make sure, for the four- or five-day window that we give people in order to get their second shot ... we need to make sure that that's available for them when they return for their second shot," she added.
But even with those considerations, there are still "millions" of doses left "sitting on the shelves," she said. "That's one of the bottlenecks and one of the ways that we have to get resources to the states, to make sure that they can quickly administer the vaccines that are on their shelves," she said.
Ohio has set aside portions of its vaccine supply specifically for vaccinating the state's K-12 staff, allocating around 55,000 vaccines to schools every week, Gov. Mike DeWine announced Thursday.
DeWine said the state is trying to do two things at once: continuing to vaccinate older Ohioans in February, while keeping school vaccinations on track.
"This plan that we have will allow most of the K-12 staff in a county to be vaccinated within seven days," DeWine said.
Service members and retirees might help with vaccinations
The Federal Emergency Management Agency plans to request as many as 10,000 service members to support vaccine administration.
Service members could be deployed at up to 100 sites nationwide to help boost administrations, a FEMA spokesperson said.
The federal government is also amending rules to help broaden the list of people who can administer vaccines, White House Covid-19 response coordinator Jeff Zients said Wednesday.
The Department of Health and Human Services "will amend the current Public Readiness and Emergency Preparedness Act -- otherwise known as the PREP Act -- to permit doctors and nurses who have recently retired or become inactive to administer shots and to permit anyone currently licensed to vaccinate in their state to administer shots across state lines," Zients said.
No signs of major safety concerns with vaccines
Severe allergic reactions to vaccines, known as anaphylaxis, are not a problem, Walensky said.
"Based on our most recent data ... we found that there were 2.1 cases of anaphylaxis per million administered doses of Moderna, and 6.2 cases of anaphylaxis per million doses administered of Pfizer," she said during a White House Covid-19 response team briefing.
"Let me be clear: These are rare treatable outcomes, and the Covid-19 vaccines are safe," she said.
It's also important to put the numbers into context and consider that the risk of getting sick with the virus is "much higher" than the risk of allergy from the vaccine, the CDC director added.
Other mild side effects, like pain in the arm, fatigue and muscle aches after the shot are "all normal and expected," Walensky said.
In fact, they're usually a good sign, the CDC director said.
"These symptoms mean that your immune system is revving up, and the vaccine is actually working."
