Public health experts recommend an annual flu shot, and are worried a “twindemic” with Covid-19 could further burden health care facilities this year.

Last fall, as coronavirus cases climbed and the world hoped for vaccines, health experts feared influenza and Covid-19 would combine for a devastating “twindemic.”.

While pandemic measures appeared to keep the flu at bay, this year experts are again concerned, especially as some countries and state authorities roll back lockdown rules.

Many officials and experts are urging the public: Do not dismiss the danger of the flu, and seek a flu vaccine.

Schaffner warned that medical providers now had to remind people about influenza: “We are going to have to say, ‘There is another nasty respiratory virus, and don’t blow it off.’”.

Scientists said pandemic precautions most likely played a role, as many people adopted masking, social-distancing and hand-washing habits.

“The lack of influenza last year was truly remarkable,” said Dr.

The relative lack of flu cases over the last 18 months could also mean that population-level immunity to the flu is lower this season, said Lynnette Brammer, the leader of the C.D.C.’s domestic influenza surveillance team.

It takes about two weeks for protection to develop after vaccination, so experts recommend getting vaccinated from September through the end of October, but even after that it is better to get the vaccine than not.

Because viruses mutate, requiring a new vaccine every year, even people who received a flu shot last year need another this year, they said.

For any given season, vaccines are tailored to the types of influenza viruses — there are many — that are circulating or most likely to be circulating.

Vaccines are intended to target specific viruses: Just as the Covid-19 vaccines are manufactured for the coronavirus, flu vaccines target influenza viruses.

Common reactions to the flu vaccine can be a sore arm, and some people might get a little tired, he said.

If you do get the flu shot and the Covid-19 vaccine at the same time, experts advise using different arms to avoid soreness, or at least spacing the injection site for each shot by at least one inch.

Antiviral treatments exist for influenza, and some patients with Covid-19 receive monoclonal antibody treatment.

Experts added that children sick with Covid-19 should not get the flu vaccine until they have recovered

Public health officials and experts said that vaccination was so important because it reduces the chances of severe, sometimes fatal illness