MILWAUKEE — Over the past year and a half, the scientific world has seen a steady flow of research updating what we know about the novel coronavirus, SARS-CoV-2, and how it affects humans.

Because the virus is so new, researchers are still grappling with many questions about its function. And because of the nature of the scientific process, no single study can completely answer those questions. Instead, new research is constantly challenging our understanding of the pandemic.

Here, we explore some recent studies that have shed new light on the virus.

CDC looks into rare cases of heart inflammation after COVID-19 vaccines

There’s a “likely association” between mRNA COVID-19 vaccines and a higher risk of heart inflammation for young people, a CDC advisory panel said last week. 

But the cases are rare, and the benefits of vaccination still outweigh the risks, experts in the Advisory Committee on Immunization Practices concluded.

Health officials on the vaccine advisory committee met after reports that some people — especially young men — were seeing higher-than-expected rates of heart issues after the Pfizer or Moderna shots. 

The CDC and FDA have confirmed 518 cases of myocarditis (or inflammation of the heart muscle) and pericarditis (or inflammation of the tissue around the heart) in people under 30 who had gotten the mRNA vaccines. Hundreds of other cases are still under investigation.

Most of these cases occurred after the second vaccine dose, and showed up within a few days, the CDC reports. For the most part, patients had mild symptoms like “fatigue, chest pain and disturbances in heart rhythm that quickly cleared up,” The New York Times reports. 

As one ACIP member told The Atlantic, the cases have seemed less severe than myocarditis that can arise from other causes (including COVID-19 itself) — and as of last week, hadn’t led to any severe outcomes or deaths.

A group of health officials, including CDC Director Rochelle Walensky, published a statement encouraging everyone over 12 years old to still get vaccinated.

“The facts are clear. This is an extremely rare side effect, and only an exceedingly small number of people will experience it after vaccination,” they wrote. “Importantly, for the young people who do, most cases are mild, and individuals recover often on their own or with minimal treatment.”

Still, the FDA added an extra warning to the vaccine fact sheets, directing people to watch out for chest pain, shortness of breath or other heart irregularities after getting their shots. And health officials said monitoring will continue to look into the possible links and keep tabs on any longer-term effects.

All eyes on the Delta variant

Just as vaccines have helped start to rein in the pandemic, a new threat has emerged to our pandemic progress: The highly contagious Delta variant. 

First identified in India, the Delta variant — also known as B.1.617.2 — is now spreading across the U.S. and raising alarms along the way. As of this week, the variant has now been detected in all 50 states and Washington, D.C.

Wisconsin has reported 71 cases of the variant as of Friday, according to DHS data. The variant still makes up a small share of the state’s cases, but is under close watch as a “variant of concern.”

Like the variants that came before it, Delta probably arose when the virus — which is constantly making small copying errors as it spreads — happened upon some mutations that gave it a leg up over other versions.

“What we’re seeing is a virus that’s becoming more efficient at making more viruses,” virologist Angela Rasmussen told The Atlantic.

Some estimates show that Delta could be as much as 50% more transmissible than the Alpha variant first discovered in the U.K. — which was already more infectious than earlier versions of the virus. The Delta variant quickly took over other strains in India and the U.K. in recent months, heping to power surges of infections there.

Walensky has said she expects Delta to become the dominant variant in the U.S in the coming weeks. So far, Delta cases account for around 25% of new infections in the U.S., she said at a federal briefing.

Though some reports have suggested Delta infections might produce slightly different symptoms, it’s still unclear whether the variant is deadlier than other versions of the virus. On the plus side, some promising studies have shown that COVID-19 vaccines seem to be working well against the variant.

One study out of the U.K. found that Pfizer’s vaccine still held strong against the Delta variant, cutting infections by 88% for fully vaccinated people. That’s a slight dip from the effectiveness rates against other variants, but still shows good protection, scientists concluded.

After just the first dose, though, the vaccine was only 33% effective against the variant — highlighting the risk to partially vaccinated people.

Johnson & Johnson also announced this week that its single-dose vaccine appeared to protect against the Delta variant. In blood samples tested in the lab, the antibodies produced by the immune system after a J&J shot were able to fight off the variant virus, researchers found.

Given Delta’s concerning rise, the World Health Organization and Los Angeles County officials encouraged people to keep wearing masks indoors, even if they’re fully vaccinated. But the CDC said its guidance — that vaccinated people can set their masks aside in most settings — hasn’t changed.

In any case, U.S. officials are urging Americans to get their shots if they haven’t yet. The pockets of unvaccinated people across the country are highly vulnerable as the Delta variant spreads — and the longer the pandemic lasts, the better the chances that even more variants will emerge.

“The Delta variant is currently the greatest threat in the U.S. to our attempt to eliminate COVID-19,” infectious disease expert Anthony Fauci said at a briefing.

Novavax shot shows strong results in late-stage trials

Could another COVID-19 vaccine option be on its way? American biotech company Novavax announced last month that its shots had a 90.4% efficacy rate in Phase 3 trials — putting it up there with the highly effective vaccines already approved in the U.S.

And the shots, which require two doses, were even more effective at stopping the worst COVID-19 outcomes: The trials found a 100% efficacy rate against moderate to severe disease.

“Today, Novavax is one step closer to addressing the critical and persistent global public health need for additional COVID-19 vaccines,” Stanley Erck, the company’s president and CEO, said in a statement.

Out of the almost 30,000 trial participants across the U.S. and Mexico, 14 people in the vaccine group got sick — all with mild illness — compared to 63 cases in the placebo group, Novavax reported.

Novavax still has to go through several steps before its vaccine could be added to the mix — from getting the results published in a full scientific study, to going through the FDA review process — so any shots in arms would still be months away. The company said it would be able to produce 150 million doses by the end of the year if approved.

The shots were “generally well-tolerated” in terms of side effects, Novavax reported, with the most common symptoms being arm pain, fatigue and headaches in the aftermath. And unlike the more sensitive mRNA vaccines, the Novavax shots can be stored at refrigerated temperatures, making them easier to transport.

The Novavax vaccine uses a different technology from the Pfizer and Moderna shots, which use genetic material to spur the immune response, and the Johnson & Johnson shots, which inject a weakened common cold virus.

In technical terms, the Novavax version is a protein subunit vaccine. It’s a type of vaccine that is already commonly used to protect against viruses like hepatitis B and HPV.

To make the shots, scientists grow copies of the coronavirus’s signature spike in cells in a lab. Then, they “harvest” those spikes and put a few of them together into groupings called nanoparticles.

The spike nanoparticles get injected into the body, along with a compound that spurs the immune response, and together they train the immune system on how to find and attack the virus.

Almost all new COVID-19 deaths are coming from unvaccinated people

Data from across the country have been showing a stark trend in recent months: Almost everyone dying from COVID-19 is unvaccinated. 

“Breakthrough” cases — those cropping up in fully vaccinated people — are making up only a tiny portion of infections, and an even tinier share of hospitalizations and deaths.

The Associated Press analyzed CDC numbers from the month of May to compare the groups. Their findings: Only 1.1% of coronavirus hospitalizations and 0.8% of deaths that month were among fully vaccinated people.

Wisconsin is seeing similar patterns. Between March and June, 95% of all COVID-19 deaths in the state were among people who were not fully vaccinated, the Milwaukee Journal Sentinel reports. 

Since the start of the year, only around 1% of cases in the state have been from breakthrough infections, DHS officials told the Journal Sentinel.

These numbers can provide some reassurance for the nearly half of Americans who are fully vaccinated, per CDC data. And overall, the country has seen its rate of COVID-19 deaths drop by 90% since the start of the year, according to a New York Times analysis. 

Still, with millions of people unvaccinated in the U.S. and the Delta variant making its way through the country, the threat of COVID-19 is not over yet. Some states with low vaccination rates are actually seeing their case rates shoot back up again — like Missouri, where hospitalizations have quadrupled in the last six weeks.

At this point, with vaccines now available to every American over 12 years old, Walensky said that any coronavirus deaths still happening are “particularly tragic.”

“Nearly every death, especially among adults, due to COVID-19 is at this point entirely preventable,” she said.

Other news to note:

• According to estimates from a new study, life expectancy in the U.S. dropped by nearly two years between 2018 and 2020 — the biggest decline since World War II. The toll was more pronounced among racial minorities, especially Black and Hispanic people.

• A preprint study suggested that COVID-19 survivors may face long-term losses of gray matter in the brain — especially in brain areas linked to senses of taste and smell.

• Some scientists warn the upcoming cold and flu season might be rough, after pandemic precautions kept people safe from immune-boosting exposures. But some viral lineages seem to have died off, which might make it easier to develop effective flu shots.

• The CDC reported that the U.S. saw a 4% drop in birth rates last year — showing how the pandemic may have accelerated the ongoing decline in annual births.