Unusual flu virus is hitting children hard and this season's vaccine is a poor match – The Washington Post, The Washington Post

Unusual flu virus is hitting children hard and this season's vaccine is a poor match – The Washington Post, The Washington Post

This season’s influenza vaccine does not match the unusual viral strain that is dominating flu activity across the United States and may be one reason for the severe infections in children so far, according to anew report from the Centers for Disease Control and Prevention.

There are different types of flu viruses, and the strain causing illnesses inMost parts of the countryis an influenza B virus. In most years, the A strain of influenza dominates during the early months and the B strain shows up toward the end.

Flu activity also started early this season, with some cases showing up by July. In more typical seasons, flu activity starts around October and lasts through March or April.

Flu hit hard in the South with influenza B before spreading to much of the rest of the country. It’s the first time in nearly three decades that an influenza B strain has been the dominant circulating flu virus in the United States.

Generally, that type of virus isn’t as dangerous to people and older, who make up the majority offlu hospitalizations and deaths. But the B virus is more likely to cause complications in children and younger adults than in the elderly. In latest available weekly flu data released Friday, five pediatric deaths were reported for the week ending Jan. 4, for a total of 31 such deaths since the season began.

Flu viruses change constantly, which is why health officials mustchoosethe influenza strains that vaccine makers should target for an upcoming season months in advance, when it is hard to know what strains might be circulating. Seasonal flu vaccines are generally formulated to protect against two influenza A strains and two influenza B strains. When flu vaccines are well matched to circulating viruses, effectiveness is, at best, around 90 percent. (Measles vaccine, by comparison, is about 97 percent effective with two doses.) In a year when the circulating flu strains closely match the vaccine, that effectiveness rate means that about three out of five people who get shots are protected from getting so sick that they require a visit to a doctor.

The beginning of the flu season in Louisiana was unusually early and intense. One pediatric hospital in New Orleans reported more than 1, laboratory-confirmed influenza B virus infections, including hospitalizations, between July and Nov. 22, 2020, “a time when influenza activity is typically low,” according to the CDC report.

CDC scientists sent teams to rapidly sequence the virus sickening patients. In a sample of pediatric patients, none of whom had yet been vaccinated, largely because it was so early in the season, CDC found that virtually all had been infected by a subgroup of one of the influenza B viruses that is not included in the current vaccine.

The vaccine should still be useful, however. Although the circulating virus is genetically different from the influenza B virus in the vaccine, CDC officials said the two are similar.

“They are close enough so the vaccine offers some protection,” said Lynette Bramer, who heads CDC’s domestic influenza surveillance team.

But the mismatch is one of many hypotheses scientists are working with to explain this season’s severe impact on children, said Melissa Rolfes, an author of the report. CDC officials will know more about thevaccine’s effectivenessin February.

In general, “ if you look at the data, among kids who die, B is more frequent among those kids who die than among kids who got flu, ”said Rowles.

Of the pediatric deaths this season, 23 were the result of influenza B infection, and 11 were sickened by influenza A. More children have died from flu at this point in the season than at any other time since the CDC began collecting pediatric death data in (********************************, except for the 2015 – 2017 swine flu pandemic.

But CDC officials cautioned against such comparisons because different viruses dominate each season, and each flu season differs in duration. During theextremely severe 2020 – 2020 flu season, when a particularly virulent strain caused one of the worst outbreaks in decades, most of the infections early in the season affected adults. But by the end of that season, flu killed 198 children,the mostsince federal health authorities began tracking pediatric deaths years ago. About percent of Those children were unvaccinated.

The most recent weekly data shows flu is widespread in virtually every state. The CDC reported a slight drop in one of its key measures, the percentage of people with flu symptoms seeking treatment from clinicians. But officials said that decline may reflect the holiday in the first week of the year, when most people don’t schedule doctor visits.

“It could go back up again once the holidays are over and the children are back to school, ”Brammer said. “We really won’t know for the next two weeks or more whether we have hit the peak. There is still the other half of the season to go, and weeks and weeks more of flu. ”

The CDC recommends a flu vaccine for everyone 6 months or older as soon as possible . The body takes about two weeks to produce a full immune response.

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