The flu vaccine cannot prevent all cases of the respiratory illness, but it appears to reduce severe outcomes — intensive care unit admissions and death — among those who are vaccinated but still become infected with the virus, say the researchers behind a newly published study.

“These data highlight the need of an influenza vaccine for each season for those people who are more likely to show severe types of influenza, such as people over 65 and people with other diseases for whom the influenza vaccine was not enough to prevent the infection from appearing,” said the researchers.

Investigators studied all of the severe cases of flu that occurred in 12 hospitals in Spain during the 2010-2011 and 2015-2016 influenza seasons. During those time frames, a total of 1,727 patients aged 18 or more years entered the hospital for flu; 591 were admitted to the ICU and 223 died.

“Results show that, among those ICU admissions and deaths, vaccination was less frequent (21.2% of the cases) than [in] the rest of the patients with more benign symptomatology, 29.7% of them being vaccinated,” the authors wrote. “Therefore, the effectiveness of influenza vaccination to prevent ICU admissions or death among the total people in hospital for influenza was of 23%, and in particular, 44 % for the group of people aged 65” or more.

Full results are published in the journal Eurosurveillance.

National Influenza Vaccination Week

The U.S. Centers for Disease Control and Prevention has declared Dec. 2-8 as National Influenza Vaccination Week to remind people that it is not too late to get vaccinated. “Flu vaccination coverage estimates from past seasons have shown that few people get vaccinated against influenza after the end of November,” according to the agency.

The Clover Health Flu Shot Monitor found that 75% of people aged 80 or more years, 66% of those aged 70 to 79, and 56% of adults aged 60 to 69 have been vaccinated so far this year. The CDC encourages long-term care and other healthcare workers to get vaccinated to help protect themselves, their families and those for whom they care, who are among the most vulnerable.

The CDC has posted a toolkit to help increase influenza vaccination among workers and an influenza outbreak management guide for long-term care facilities on its website.