The current wave of the omicron variant of the coronavirus making its way across the U.S. — dominated by the subvariants BA.4 and BA.5 — is sparking new concerns about a seemingly endless cycle of Covid infections.

Although there are still uncertainties about the different versions of the omicron variant, experts have a clearer understanding about it and how it affects people who are vaccinated or unvaccinated or who have previously had cases of Covid.For most people, at least those who are up to date on their Covid vaccinations, the original type of the omicron variant caused a milder illness that resembled the common cold, another form of the coronavirus.

Anecdotally, doctors say, the symptoms of the BA.4 and BA.5 subvariants are mostly similar to those of the earlier version of the variant.

"As far as we can tell, the BA.5 has not really proven too much different from the previous omicron waves," said Dr. Bernard Camins, the medical director for infection prevention for the Mount Sinai Health System in New York. "We just know that it's more contagious."

Dr. Roy Gulick, the chief of infectious diseases at Weill Cornell Medicine in New York, said typical symptoms of the omicron subvariants include:

• Sore throat
• Hoarse voice
• Cough
• Fatigue
• Nasal congestion
• Runny nose
• Headache
• Muscle aches With the original version of the omicron variant, which swept across the U.S. at a dizzying speed last winter, the loss of taste and smell was not as common as with the earlier alpha and delta variants. However, with the spread of BA.4 and BA.5, that symptom seems to have returned, some doctors note.While the omicron variant may have appeared milder during the winter Covid wave, that could have been a reflection of the groups who were getting sick: the young and otherwise healthy, as well as those who were fully vaccinated.

  “It is clear that if you’re vaccinated, particularly if you’ve had a booster, omicron tends to produce milder infections,” Dr. William Schaffner, an infectious disease expert at the Vanderbilt University Medical Center in Nashville, Tennessee, said this year.

  For people who have been vaccinated but have not had boosters, typical symptoms include more coughing, more fever and more fatigue than for those who have received extra doses, said Dr. Craig Spencer, the director of global health in emergency medicine at NewYork-Presbyterian/Columbia University Medical Center.

  The Centers for Disease Control and Prevention has recommended that people ages 50 and older should get second Covid booster shots to protect against waning immunity from the vaccines.

  Because BA.5 is so contagious and it appears to dodge the body’s immune system, people are more vulnerable to reinfection with Covid, especially if it has been more than 90 days since the previous illness.

  “Previous infection doesn’t guarantee protection anymore,” said Camins of Mount Sinai. 

  For the most part, reinfections are likely to be less severe than previous infections, thanks to higher levels of immunity, experts say. There has been evidence that the omicron variant tends not to burrow deeply into the lungs as much as previous variants. A study, which was posted online by the University of Hong Kong and has not yet been peer-reviewed, found that while the omicron variant is less severe in the lungs, it can replicate faster higher up in the respiratory tract.

  In that way, it may act more like bronchitis than pneumonia, said Dr. Hugh Cassiere, the director of critical care services for Sandra Atlas Bass Heart Hospital at North Shore University Hospital on Long Island, New York.

  "Usually patients with acute bronchitis tend not to be short of breath. They tend to cough and produce sputum," he said. "Patients with pneumonia tend to be short of breath and feel more fatigued than bronchitis in general."

  A small study from the CDC found that people who had Covid and are later reinfected with the omicron variant may experience fewer symptoms than they did during their initial bouts with the virus.

  Still, it is virtually impossible for people to rely on symptoms to self-diagnose an illness. Doctors urge people who have any cold symptoms or flulike symptoms to get tested.