It may be spring, but virus season isn’t over yet.
The flu and Covid, including a new strain called BA.3.2, nicknamed “cicada,” are still circulating, along with several other respiratory illnesses and a nasty stomach bug that leaves many Americans feeling dirty.
The symptoms of most viruses are so similar — wheezing, coughing, muscle aches, fever — that doctors say you can’t really tell what you have without a test.
Influenza A was really bad in the US at the end of last year, driven by the H3N2 subclade K strain. As it started to spread in January, “we switched to seeing some of these other viruses,” said Marlene Wolfe, an assistant professor of environmental health at Emory University. “Every year we think of fall, winter and spring as the season of respiratory illness,” he added, “but the truth is that there are different viruses that appear in every season.”
Arkansas, North Dakota, Vermont and Wyoming are still experiencing a moderate number of respiratory infections, and infections are low elsewhere in the country, according to the latest data from the Centers for Disease Control and Prevention.
Cases of RSV, or respiratory syncytial virus, remain high in some states, including Michigan, Nebraska, Nevada, South Dakota, Tennessee, West Virginia and Vermont.
What disease do I have?
“Unfortunately, there is really no distinguishing feature between these respiratory diseases,” said Dr. Greeta Sood, an epidemiologist at Johns Hopkins Bayview Medical Center in Baltimore.
Symptoms of Covid are no longer marked by loss of taste and smell as they were in the first few years of the epidemic, he said.
“And we can’t predict, like before, what a person has based on what’s circulating. It could be Covid, it could be the flu, and now we’ve added long RSV to the mix,” Sood said.
Right now, data on the location of wastewater, which measures the prevalence of various bacteria in a community, may be able to tell which virus you might have.
“It’s not quiet in these diseases compared to other years, but where you live there may be more opportunities,” said Jennifer Nuzzo, director of the Pandemic Center at Brown University School of Public Health.
Wolfe agreed that it’s important to understand what viruses are circulating in your community, as this can vary greatly from state to state.
“The dynamics of when and where we see the most cases varies from virus to virus, so it’s important to know what’s happening in your community. We still have a lot of respiratory viruses right now that tend to circulate in early spring,” she said.
Do I have Covid?
The masks are gone. Relatively few people got the new Covid vaccine this winter, in part because of confusion over who was eligible to get it.
The CDC has reported that a highly mutated variant of Covid called BA.3.2 has been found in contaminated water and nasal swabs in 25 states. A different spike protein carries a mutation that experts worry could allow it to avoid immunity from previous infections or booster shots.
“This variant is very different compared to previous variants, and whenever that happens, there is always a risk that because we have less immunity in this body, it can cause a spike in cases,” said Sood.
Only about 0.55% of the Covid viruses picked up in the US since mid-March have been of the BA.3.2 variant, the CDC’s most recent data shows. Covid cases have not increased in Europe following the first case of BA.3.2 detected last April, the agency reported. Currently, CDC data shows that Covid cases, although at a low level, are increasing in Florida and Massachusetts, while decreasing in the rest of the country.
In the US, “Covid cases overall don’t look like they’re increasing,” Sood said, adding that it’s too soon to say whether BA.3.2 will cause more Covid cases. “There have been a number of similar variants that are very different immunologically, and we haven’t seen a wave.”
CDC data shows mixed Covid cases across the country. Their numbers are high or moderate in parts of the South, Midwest, DC and Appalachia, and low in the West and Southeast. Data from WastewaterSCAN, a public health program that collects wastewater monitoring data, shows an increase in Covid cases.
“Covid has not yet entered a predictable pattern,” Nuzzo said, adding that the slight increase in Covid cases in certain states “is not something to be alarmed about. We are not seeing anything in terms of a trend for Covid right now.”
Still, people at high risk of complications should consider getting a booster every six months or so, she said.
“I have timed the Covid boosters for traveling, when I really don’t want to get Covid, or when the local numbers are going up. People have to look at different things in their lives, based on local habits and other circumstances,” said Nuzzo.
Influenza
The early spike in flu cases this season was driven by a modified influenza A, or H3N2, strain called “subclade K.” Cases peaked between Thanksgiving and early January, and some experts fear the US will repeat last year’s deadly flu season, which killed nearly 800 children and teenagers.
“It didn’t get as bad as last year’s flu season, which doesn’t mean anything, since last year was the worst in history,” said Nuzzo. “Last year, more children died from the flu than in any other year including 2009, when we had a flu epidemic.”
The CDC has recorded 115 pediatric flu deaths so far this flu season, after two record years. The 2023-24 flu season killed 199 children and youth, matching the previous record set by the 2019-20 flu season. However, these diseases still prove fatal – a California teenager died in early March from the flu, one of 14 children who died that week.
Cases of Influenza A began to decline in January and continue to decline across the country, although this strain still causes disease and accounts for the majority of cases. Influenza B cases are increasing in Washington and North Dakota, but decreasing nationwide, according to CDC data. WastewaterSCAN data showed the opposite – that influenza B infections are still high across the country and increasing.
“Influenza B still shows up in wastewater all the time,” said Wolfe, who is also director of the WastewaterSCAN program.
Sood said there is still time to get the flu vaccine, especially for people who got their last one in early fall.
“If you’re going to travel and want to get the vaccine, it’s not too late, but we’re closer to the end of the season than the beginning of the season,” Sood said.
Respiratory syncytial virus (RSV)
Respiratory syncytial virus, or RSV, can cause a bad cough and runny nose and fever. Although it may be difficult to distinguish from the common cold, RSV can be dangerous to children and infants.
This season, “RSV is rampant, but we’re still seeing a little bit of it in the wastewater,” Wolfe said.
CDC wastewater data show that, overall, RSV is circulating at moderate levels across the country, but the virus is still high or very high in Hawaii, Iowa, Michigan, Minnesota, Nebraska, Nevada, New Hampshire, South Dakota and Wyoming. Cases are still growing in North Dakota.
“RSV usually comes early in the season, which it did, but what’s unusual about RSV right now is that they don’t go down the way we expected,” Sood said. “Some states still recommend that babies born now should get RSV antibodies, usually the RSV season will be considered over now.”
Human metapneumovirus (HMPV)
Human metapneumovirus, or HMPV, is a virus related to RSV that causes symptoms similar to the common cold. According to WastewaterSCAN, HMPV is circulating at high levels across the country — although this is to be expected, Wolfe said.
“HMPV is consistent in wastewater data, and tends to peak in mid-April,” she said.
Norovirus, the ‘disease of two buckets’
Of the most common viruses right now, you’ll know if you have norovirus. Although it is sometimes called the stomach flu, it is a stomach virus, not a respiratory one. A nasty, highly contagious bug has been at high levels for months and is still causing misery. In the latest outbreak, more than 150 people, including passengers and crew, aboard the Princess cruise ship became ill with norovirus, according to the CDC.
People with norovirus suddenly come down with vomiting, diarrhea and nausea, which usually last for several days, earning the name “two-bucket disease.”
WastewaterSCAN shows that norovirus burdens are still high across the country but not increasing. Last cold and flu season, the US experienced an unusually high number of norovirus cases, Wolfe said. So far, the CDC has recorded less than half the number of norovirus cases this season compared to last.
“This year what we are seeing looks very similar to the pattern we saw before,” he said. “We saw the norovirus peak in late February and the cases seem to be going up. It’s good to see that it’s not as bad as it was last year.”
