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Flu vaccine appears to be offering reasonable levels of protection this winter, with particularly strong levels in children, new data from the Centers for Disease Control and Prevention suggest.

The vaccine effectiveness estimates, which showed unusually robust protection for children against influenza B viruses but more modest protection for people ages 65 and older against influenza A viruses, were presented Wednesday at a meeting of the CDC’s expert vaccine panel, the Advisory Committee on Immunization Practices.

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The figures were based on data from four national databases, and a separate analysis from California.

This flu season is ongoing and these estimates are preliminary. The CDC will reassess the vaccine’s effectiveness later in the year, after the season ends. That said, flu activity appeared to peak over the Christmas holidays, and has been declining slowly since then. The CDC has assessed this flu season as being of moderate severity.

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In children, the vaccine effectiveness against any type of flu infection requiring medical care ranged from 59% to 67%, depending on the database. Protection against illness serious enough to require hospitalization ranged from 52% to 61%.

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The vaccine effectiveness in children against influenza A H1N1 viruses — the type that has predominated this flu season — ranged from 54% to 61% against flu infection requiring medical care and between 64% and 89% in protecting against infection with influenza B. Flu B viruses have made up a minority of circulating viruses this year, though they have been seen more commonly in the past few weeks.

In all adults, the vaccines appeared to offer strong protection against flu B virus, with a vaccine effectiveness of 78% against illness requiring medical care and 60% against illness serious enough to require hospitalization. Robust protection was even seen in adults aged 65 and older, a group in whom flu can cause serious illness but in whom vaccines may not generate as much protection as they do in younger adults.

The effectiveness of the vaccines against H1N1 viruses was lower, estimated to be 25% against any illness requiring medical care and 50% against flu requiring hospitalization in all adults. The vaccine appeared to be somewhat more effective in adults 65 and older, who are recommended to get specially formulated shots that either contain a high dose of vaccine or include an adjuvant, a boosting compound.

The CDC recommends that everyone 6 months and older should get vaccinated against flu annually. But vaccine uptake has been declining since the Covid-19 pandemic. The CDC estimates that 51% of children and 48% of adults have received flu vaccine this year, with the rate among people ages 65 and older at nearly 74%.