The Centers for Disease Control and Prevention is recommending that children aged 6 months to 4 years, schoolchildren, pregnant women, persons over 50 years old, residents of nursing homes or other chronic-care facilities should be vaccinated against the flu.

Because it can take two weeks to develop full immunity after receiving a flu shot, those at highest risk should be vaccinated during the month of October, public health officials say. The CDC recommend getting a flu shot because it will lessen the severity of the infection and protect against serious complications. Influenza is a viral illness and its symptoms include fever, cough, chills, sore throat, headache and muscle aches.

Record numbers of vaccinations are expected this year, though last year’s vaccine was just 44 percent effective.

A study led by Dr. Mark Steinhoff, a paediatrician with the Johns Hopkins University Bloomberg School of Public Health showed that flu shots offer protection during pregnancy for both mother and baby. “Infants under six months have the highest rates of hospitalization from influenza among children in the U.S. These admission rates are higher than those for the elderly and other high-risk adult groups,” Steinhoff said.

The infections are mostly treatable in adults, but usually deadly in very young children. In the past years, the U.S. Advisory Committee on Immunization Practices recommended that children 6 months to 4 years be vaccinated because they are among the high-risk groups and are more likely to suffer serious complications associated with the flu. Schoolchildren should be vaccinated because they are big spreaders of flu. By targeting them, officials hope to reduce outbreaks in communities.

Reports show that more than 35,000 Americans die from influenza, which is especially dangerous for young children, or for those with a weakened immune system.