Click here to see all of PopSci’s COVID-19 coverage.

Vaccinated Americans will once again be able to visit Canada, but the US is keeping its side of the border locked as Delta continues to drive up new cases, especially in the South. Meanwhile, it’s becoming evident kids can get long COVID, too, and some Americans are taking it upon themselves to get unauthorized booster shots. 

Here’s the latest on the week’s COVID news. 

Halfway to full vaccination nationwide, but cases remain on the rise

Months after COVID-19 vaccines were first made widely available to the public, the US has finally arrived at a prominent milestone: 50 percent of the country’s population is fully vaccinated. 

This proportion, however, is not distributed evenly across states: Vermont is leading the charge, with 68 percent of its population fully vaccinated, while Alabama and Mississippi are bringing up the rear, with just 35 percent each. 

As vaccination rates slowly progress, the highly contagious Delta variant is ravaging states with lower vaccine uptake. Florida, where 49 percent of residents are fully vaccinated, reported 23,903 new cases on Friday, the state’s highest single-day total since the start of the pandemic. In Florida hospitals, 44 percent of ICU beds in the state are occupied by COVID-19 patients, NPR reported, compared to just 19 percent nationwide. 

Cases have nearly doubled in Louisiana over the past two weeks, where only 37 percent of individuals are fully vaccinated.

[Related: What the CDC’s new mask guidance means for you]

The rest of the country is in bad shape as well. The US is reporting an average of more than 110,000 new cases per day for the first time since February, and COVID-19 deaths nationwide have nearly doubled since two weeks ago. 

While the vast majority of new cases have been recorded in unvaccinated people, so-called breakthrough cases in vaccinated individuals can happen, and are occurring more frequently thanks to the Delta variant. 

Get vaccinated, even if you’ve had COVID before

Unvaccinated individuals who were previously infected with the coronavirus are more than twice as likely to get re-infected compared to individuals who were previously infected but received the vaccine earlier this year, according to a new CDC investigation

While previous studies have shown that antibodies produced during an unvaccinated individual’s immune response to the virus offer some protection against reinfection, this new report supports the claim that vaccines offer more consistent and robust protection than natural antibodies alone.

[Related: What you need to know about variants, vaccines, and breakthrough COVID cases]

The study relied on data from the state of Kentucky, and compared pooled case data from March to December 2020 with pooled case and vaccine data from May and June of this year. It tracked individuals that recorded a positive test during the first time period and another during the second, and compared it with a control group of people who were infected last year but did not report a second positive test this spring.

Only 20 percent of the twice-infected group were vaccinated, compared to 34 percent of those who did not contract a second infection—suggesting that unvaccinated individuals are more likely to encounter a second infection. The authors conceded, however, that the scope of the study is limited and should be repeated with a larger data set.

The researchers urge that all eligible people should receive a COVID-19 vaccine to reduce the likelihood of infection, even if a person has already contracted the virus, especially in light of the circulation of the contagious Delta variant. 

The CDC advises that unvaccinated individuals who have contracted COVID-19 wait until symptoms have improved and at least ten days have passed since their positive test to get vaccinated. Individuals who were treated for the virus with monoclonal antibodies or convalescent plasma should wait 90 days before receiving a shot.

Kids can suffer from long COVID, too

Despite early reports that most kids won’t get super sick if they contract the virus, experts and families remain concerned about the possible aftermath of so-called long COVID. 

A UK-based study, published in The Lancet last week, reported that 5 percent of children aged 5 to 17 who contracted COVID-19 experienced symptoms for at least 28 days following a positive test. This proportion fell to 2 percent after 56 days, according to the study. Prolonged symptoms were less prevalent among younger children. 

Although current understanding of long COVID is limited, it’s widely accepted that the phenomenon is much more common in adults than in children. Its infrequency, however, does not detract from how scary some of the prolonged symptoms can be for kids. 

The New York Times this week reported on the anecdotes of teenagers experiencing new, intense memory lapses, elevated anxiety, extreme fatigue, and regular nausea in the wake of a coronavirus infection.

[Related: Kids make up 19 percent of new US COVID-19 cases now]

“The potential impact is huge,” Avindra Nath, chief of infections of the nervous system at the National Institute of Neurological Disorders and Stroke, told the Times. “I mean, they’re in their formative years. Once you start falling behind, it’s very hard because the kids lose their own self-confidence too. It’s a downward spiral.”

In an effort to decipher the unknowns of pediatric long COVID, the National Institutes of Health announced last month that they have allocated $40 million for a study in conjunction with Children’s National Hospital in Washington, D.C., to study long COVID in kids. 

“You need a very focused, large-scale effort that really has a standardized approach to find the answers,” Bill Kapogiannis, program director in the NIH’s Maternal and Pediatric Infectious Disease Branch, told CNN.

In a further push to protect kids from initial infection as they head back to school in the fall, the CDC updated their masking guidelines late last week. “Due to the circulating and highly contagious Delta variant, CDC recommends universal indoor masking by all students (age 2 and older), staff, teachers, and visitors to K-12 schools, regardless of vaccination status,” the update reads. 

Vaccinated Americans can travel to Canada starting today

Our neighbors to the north are allowing vaccinated visitors to enter as of August 9, with a few pre-travel requirements. In addition to being fully vaccinated and providing proof as such, travelers are required to submit a negative COVID-19 test before travelling. 

This information must be submitted online before boarding a flight or crossing the land border. Submission of falsified documents can result in heavy fines. Children under the age of 12 who are unvaccinated may enter with a fully-vaccinated parent or caretaker.

[Related: The safest ways to show proof of vaccination, wherever you are]

While fully-vaccinated travelers are not required to quarantine upon arrival, individuals exhibiting symptoms will be asked to do so, and all travelers are required to provide a prepared quarantine plan prior to arrival. Visitors are expected to comply with all local public health guidelines, including mask mandates in certain provinces like Quebec and Ontario.

The US has yet to reciprocate the lift on travel restrictions and will continue to restrict visitors from Canada until at least August 21. The border closure was extended late last week, before which it was set to expire last Thursday.

Despite lack of FDA approval, some Americans are getting booster shots

Several hundred Americans have sought out and received an additional dose of one of the mRNA vaccines in recent weeks, The Associated Press reported. The full extent of third dose administration is unknown since reporting is voluntary, but an AP investigation mapped at least 900 instances of people getting a third dose in a vaccine-tracking system maintained by the CDC. 

[Related: Will we need booster shots? And other questions about the Delta variant, answered.]

Uncertainty about boosters is widespread. Some have cited concerns about the circulating Delta variant as their motivation for receiving a booster, despite the fact that they are not approved nor recommended by the FDA. 

San Francisco public health officials said last week that they would provide a dose of the Pfizer or Moderna vaccine for individuals who received the single-dose Johnson & Johnson shot, framing it as a supplement rather than a booster.

Several research institutes are actively looking at the effects of boosters for at-risk groups, while Pfizer initiated the process of seeking FDA approval for a third shot last month.  

“The verdict is still out on whether the general population might need them,” Michelle Barron, senior medical director for infection prevention at UCHealth in Colorado, told AP.