This week, with 2.8 million doses of the newly-authorized Johnson & Johnson COVID-19 vaccine in tow, 17.6 million coronavirus vaccine doses in total will be shipped out across the United States, a marked improvement from the 10 million doses the country was averaging just a month ago.

States are also getting those shots into people's arms more quickly now. On both Saturday and Sunday, more than 2.3 million received a vaccine dose, suggesting that at least 3 million people could be getting a shot daily by the end of March, The New York Times reports.

Now, there's cautious optimism among experts that herd immunity could be on the horizon, and the single-dose Johnson & Johnson shot appears to be a major reason why. Per Vox, if one-third of vaccines are one-shot and the U.S. is administering 3 million doses per day, the U.S. could reach 80 percent immunity by mid-summer.

The Mayo Clinic's Vincent Rajkumar estimates that, at this point, around 140 million people will need to be vaccinated to reach herd immunity, a goal he predicts could be achievable within three to four months. Rajkumar said his estimate is likely conservative since the actual number of people who have already been infected is probably much higher than what's been recorded.

There are several caveats, including lingering vaccine hesitancy and uncertainty over variants' ability to resist immunity, but the U.S.'s much-maligned vaccine rollout looks to be on the upswing. Tim O'Donnell

Back in 2008, Sean Kazmar Jr., then a 23-year-old middle infielder, played 19 games in the big leagues for the San Diego Padres. Flash forward to Saturday, nearly 13 years later, and he's getting another shot in the show.

Kazmar never made it back up to a Major League roster after his cup of coffee all those years ago, but the 36-year-old just got the call from the Atlanta Braves. If and when he gets into a game, he'll have had the longest break between MLB appearances since 1950, surpassing legends like Satchel Paige and Minnie Miñoso, who were called out of retirement for very brief stints in their 50s.

Kazmar, though, wasn't retired. He was grinding it out in the Minor Leagues, most recently for Atlanta's AAA team, the Gwinnett Braves.

The reason for Kazmar's perseverance is reportedly because he wanted his kids to see him play in the majors. They got the chance; Kazmar pinch hit in the 5th inning during the Braves' matchup with the Chicago Cubs on Saturday.

This story has been updated to reflect Kazmar's appearance. Tim O'Donnell

In the early stages of the coronavirus pandemic, some small-scale studies found high rates of myocarditis, or heart inflammation, among college athletes who had previously tested positive for COVID-19. That prompted some universities to do cardiac testing on all athletes who were infected throughout the year, but a new study released Saturday suggests such "blanket testing" is unnecessary, ESPN reports.

Among the 3,018 athletes examined in the study, only 21 exhibited signs of possible, probable, or definite myocarditis, and those who did have heart issues were more likely to have had moderate COVID-19 and/or cardiopulmonary symptoms during the infections.

Dr. Jonathan Drezner, the director of the University of Washington Medicine Center for Sports Cardiology and a co-principal investigator of the study, said the results indicate athletes who had mild or no COVID-19 symptoms probably don't need to be screened for myocarditis. "I would simply be comfortable doing a good review of symptoms," he told ESPN, adding that their health should still be monitored "when they get back to play." Read more at ESPN. Tim O'Donnell

Congress has gone nearly 80 days without a member announcing a positive coronavirus test, having crossed the 75-day threshold on Wednesday, The Washington Post reports.

There were a fair number of cases in the Capitol in the fall and early winter when the U.S. as a whole was experiencing a significant surge, but Rep. Stephen Lynch (D-Mass.) was the last lawmaker to reveal he had contracted the virus on Jan. 29. That's the longest stretch without a publicly confirmed infection in the House or Senate since the pandemic began, the Post notes.

While it's too early to jump to conclusions and declare that Congress has reached herd immunity, the decline has coincided with COVID-19 vaccines becoming widely available to lawmakers in recent months, which suggests the shots are doing their job, as some targeted studies have found to be the case in other workplace environments, like hospitals. Read more at The Washington Post. Tim O'Donnell

Presiding over Prince Philip's intimate funeral on Saturday, the dean of Windsor (the spiritual head of St. George's Chapel at Windsor Castle) praised the Duke of Edinburgh's "kindness, humor, and humanity," as well as his "unwavering loyalty" to Queen Elizabeth II and his service in the Royal Navy.

The tribute was concise and, as per Philip's request, the dean did not deliver a sermon.

Only 30 people, including Philip's grandsons William and Harry, were at the ceremony in person because of coronavirus restrictions. The attendees wore masks and remained socially distanced, based on households. The queen sat in a section of a pew by herself, which prompted several people to comment on how the "striking" scene was representative of how many people have had to grieve this last year because of the pandemic. Tim O'Donnell

NASA on Friday tapped SpaceX to help bring humans back to the moon later this decade as part of its Artemis Program.

The agency announced Friday that it will award Elon Musk's company a $2.89 billion contract for the development of its Starship vehicle, an uncrewed flight test to the moon, and, finally, a crewed mission that will land on the lunar surface. SpaceX beat out Dynetics and Jeff Bezos' Blue Origin for the opportunity, thanks in large part to its affordability. SpaceX's bid cost about half of Dynetics' and a quarter of Blue Origin's, Ars Technica reports. So while Starship has plenty of innovative features that made it an enticing candidate, "budget appears to have been the biggest factor" since NASA has struggled to secure funding from Congress for the lunar landing.

Ars Technica suggests NASA likely isn't done, however, explaining that "a sole-source award to SpaceX for the Human Landing System will certainly not be particularly popular in Congress, where traditional space companies such as Lockheed Martin and newer entrants like Blue Origin have more established lobbying power." In other words, the move "sends a clear message from NASA and the White House" — which has endorsed the Artemis Program and its goals — "to budget writers in the House and Senate." Read more at Ars Technica. Tim O'Donnell

For the first time in 60 years, Cuba will soon be without a Castro in a formal, day-to-day leadership position.

Raúl Castro, the younger brother of the late Fidel Castro, confirmed Friday that he's stepping down from his role as the leader of the country's Communist Party, with President Miguel Diaz-Canel expected to take on double duties, as the Castro brothers did before him. The younger Castro, who is 90, is poised to remain an influential figure on the island, but he likely won't interfere with daily governance, The New York Times notes. That means a new era is on the horizon, as Cuba faces challenges from both the coronavirus and a struggling economy.

The next generation of leadership could allow for more free-market activity, a path that's not completely new for Cuba; Raúl, who is considered more pragmatic than his brother, began the process of implementing some reforms following Fidel's death in 2011, but it's been a slow grind. There's no guarantee a new regime will change that — Richard Feinberg, a professor at the University of California, San Diego, told Al Jazeera that he thinks it's the "worst possible moment" for reforms because the government has "no money."

That said, urgency may rule the day in a post-Castro world. Arturo Lopez-Levy, the author of Raul Castro and the New Cuba: A Close-Up View of Change and an assistant professor at Holy Names University, told Al Jazeera that, unlike the brothers, their successors will have to "rely on performance — not on historical legacy — to exercise power and as a source of legitimacy." Read more at The New York Times and Al Jazeera. Tim O'Donnell