(CNN) Despite hopes of widespread vaccinations this year, experts warned the start of 2021 would be a very rough time in this pandemic.
It turns out the first two weeks have been abysmal.
The United States just shattered its all-time records for the most Covid-19 infections, hospitalizations and deaths reported in one day:
-- On January 2, a record-high 302,506 new infections were reported in one day, according to Johns Hopkins University.
That's an average of 3.5 people getting infected every second.
-- On January 6, a record-high 132,447 patients were hospitalized with Covid-19, according to the Covid Tracking Project.
Many hospitals are now filled beyond capacity, meaning even those without Covid-19 -- say, car accident victims -- might not get immediate care.
-- On January 12, a record-high 4,462 Covid-19 deaths were reported in just one day, according to Johns Hopkins.
A Boeing 747 can carry about 400 passengers. That means in one day, US deaths from Covid-19 were on par with 11 jumbo jets crashing, killing everyone on board.
People are letting their guard down due to pandemic fatigue. And many of those who are sick of taking precautions are getting sick.
Now that the weather is colder, more people are socializing indoors. And the coronavirus primarily spreads during close contact with others through respiratory droplets -- produced when someone talks, coughs, sings or even breathes.
Sometimes, viral particles can "linger in the air for minutes to hours," the US Centers for Disease Control and Prevention said.
"These viruses may be able to infect people who are further than 6 feet away from the person who is infected or after that person has left the space," the CDC said.
Socializing indoors with anyone outside your bubble -- even just one friend -- is risky. Gathering with multiple friends indoors can be dangerous.
"If you go to a party with five or more people, almost certainly there's going to be somebody with Covid-19 at that party," said Dr. Peter Hotez, dean of the National School of Tropical Medicine at Baylor College of Medicine.
One reason why the coronavirus spreads so easily is because people can be contagious without knowing they're infected -- and can pass along the virus without looking or feeling sick.
The CDC estimates more than 50% of all infections are transmitted from people who aren't showing symptoms.
"This means at least half of new infections come from people likely unaware they are infectious to others," the agency said.
And just like doctors predicted, holiday travel and gatherings have triggered new waves of infections, hospitalizations and deaths across the country.
Fallout from the holidays could still ripple across the United States for weeks to come.
"It takes two to three weeks for patients to get sick enough to need the hospital after they've gotten the virus," said Dr. Anish Mahajan, chief medical officer at the Harbor-UCLA Medical Center.
Even though Christmas was less than three weeks ago, "we're already full."
"We don't have any more ICU capacity," Mahajan said. "All of the hospitals in the region are putting ICU patients in unusual places in the hospital just to find room for them."
New for 2021: The United States has confirmed at least 76 cases of a highly transmissible variant of the coronavirus that was first detected in the United Kingdom.
Those US cases were found in 12 states: California, Florida, Minnesota, New York, Colorado, Connecticut, Maryland, Texas, Pennsylvania, Indiana, Wisconsin and Georgia, according to CDC data posted Wednesday.
But the real numbers could be much higher because the United States lags behind dozens of other countries in the proportion of Covid-19 cases that are analyzed through genetic sequencing.
And the United States ranks 61st in how quickly virus samples are collected from patients, analyzed and then posted to an international database to find new variants.
Earlier this month, a CDC official said the agency plans to double the number of samples it sequences by mid-January -- with a target of 6,500 per week.
Understanding the genetic makeup of a virus and how it changes is critical to ensuring vaccines remain effective.
All viruses mutate over time, and new variants are common.
But scientists advising the UK government have estimated that the variant could be up to 70% more effective at spreading than others.
While it may be more transmissible, there's no evidence this variant first detected in the UK is deadlier or causes more severe disease, the CDC said.
But the strain first detected in the United Kingdom isn't the only one causing concern.
A variant first detected in South Africa has been shown it might be able to escape some of the antibodies produced by a Covid-19 vaccine.
That strain was first spotted two months ago in South Africa and has been found in 12 countries. As of Thursday, it has not been detected in the United States.
The vaccine rollout is happening more slowly than expected.
The Trump administration initially said it aimed to vaccinate 20 million people by the end of 2020.
That didn't happen. Not even close.
As of Thursday morning, about 10.2 million vaccine doses had been administered, out of roughly 29.3 million doses that have been distributed across the United States, according to the CDC.
And the two vaccines distributed in the United States right now -- from Pfizer/BioNTech and Moderna -- require two doses for each person.
The federal government recently said it will stop holding back doses kept in reserve -- intended to help guarantee second doses -- so more people can get their first dose faster.
But either way, millions of Americans will have to wait months before getting a vaccine.
If you want to get life closer to normal (and more quickly), it's time to double down on safety measures:
Wear a mask in public and every time you're around someone who doesn't live with you. If there's a chance for infection within your home, wear a mask at home, too.
Don't count on a negative test result as a way to "safely" see friends or relatives. You can test negative but still be infected and contagious.
Keep social distancing. Wash your hands frequently. And don't think you're invincible -- even if you're young and healthy.
"We see severe illness among healthy, young adults with no apparent underlying causes," Hotez said.
"Whether that's due to ... a higher dose of the virus, whether they have genetic alterations they don't know about -- we just don't understand," he said.
"So, we can't reliably predict who's going to handle this virus well, and who doesn't."