Some doctors believe COVID-19 restrictions that kept many people at home over the last two years reduced the number of flu cases.

However, many countries have removed pandemic restrictions. Now, cold weather is coming to the northern half of the world, and doctors think the upcoming winter may bring a bad flu season.

Flu, short for influenza, causes millions of infections in the U.S. each year. The U.S. Centers for Disease Control and Prevention reports the number has been as low as 9 million and as high as 40 million depending on recent years.

Doctors in the U.S. expect to give out about 180 million flu shots this year. They are asking seniors, or people older than 65, to get a special, stronger flu shot if it is available where they live.

Flu shots are recommended in the U.S. for people starting at six months of age.

Richard Webby is a doctor who centers his work on the flu at the St. Jude Children's Research Hospital in Memphis, Tennessee. He said older people should ask for the kind of shot that is right for their age group. He said three of the shots available this year work better for older people.

Younger people have choices, too. There are versions of the flu vaccine that work for people who are allergic to eggs and those who do not like injections.

Strong flu season ahead

Another flu expert is Dr. Andrew Pekosz of Johns Hopkins in Baltimore, Maryland. He said Australia recently had its worst flu season in five years. Pekosz said what happens in the southern half of the world can help predict what will happen in the northern half of the world.

He said a strong flu is dangerous for young children who have never gotten the virus before.

Jason Newland is a children's doctor who works on infectious diseases at Washington University in St. Louis in the state of Missouri. He said doctors are already treating children for infections like flu that affect the lungs. He said, "...we will see a true influenza season like we saw before the pandemic."

The doctors said one reason for increased infections is that most people are no longer wearing face coverings. During the main part of the COVID-19 pandemic, they did.

The CDC said people should get a flu vaccine by the end of October. But the agency said the shot can still be effective later in the year.

Current vaccines take longer to make because scientists must grow the virus that will be used in the vaccine in a laboratory. Sometimes, the version of flu will change, or mutate. That means the vaccine become less effective.

Future vaccines

Companies that made the vaccines for COVID-19 are now working on flu vaccines. That makes medical observers hopeful that doctors will be able to contain the flu more easily each year.

The mRNA vaccine technology, which is used by Pfizer-BioNTech and Moderna, is currently being tested for flu. If the tests are successful, scientists believe the mRNA vaccines will be able to be changed quickly if the flu virus changes.

I'm Dan Friedell.

Dan Friedell adapted this story for VOA Learning English based on a report by The Associated Press.

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shot –n. injecting a medicine or vaccine into the body using a needle

allergic –adj. related to a condition caused by a strong reaction to some substance which includes swelling or breathing problems