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PHILADELPHIA (CBS/CNN) — An increase in flu activity over the last week has led to school closures in at least 12 states, including New Jersey. A report released Friday by the Center for Disease Control and Prevention shows an increase in “widespread” flu activity in the state.

The recent outbreak squashed CDC hopes that flu activity had peaked earlier in the season.

There have been as many as 11.4 million flu illnesses, 5.4 million medical visits and 136,000 flu hospitalizations between October 1, 2018 and January 19, 2019, according to the weekly flu report released Friday by the US Centers for Disease Control and Prevention.

During the week that ended January 19, the CDC reported three additional children had died due to flu-related causes, bringing the total number to 22 for the season. For adults, flu deaths are estimated based on pneumonia and other illnesses related to flu. The proportion of deaths attributed to pneumonia and flu was 7.2%, which is slightly higher than the usual threshold of 7.1 percent for this time of year, the CDC said, based on data from the National Center for Health Statistics.

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Flu activity is expected to remain elevated for weeks, with 18 states and New York City experiencing high activity last week, an increase over the previous week when only nine states reported the same.

States reporting widespread activity rose from 30 to 36 during the same week over the previous one, with an additional 11 states and Puerto Rico reporting regional activity.

The CDC also recorded 14.8 hospitalizations per every 100,000 people for the week ended January 19. This is the overall rate with a higher proportion of people who are 65 and older requiring hospitalization (38.3 per every 100,000), followed by children up to age 4 (26.5 per every 100,000).

Over the past five seasons, the end-of-season hospitalization rates have ranged from 31.4 per 100,000 (2015-2016) to 102.8 per 100,000 (2017-2018).

About 55 million students and 7 million staff attend the more than 130,000 public and private schools each school day in the United States, according to the CDC. No government agency tallies the number of flu-related school closings; however CNN has unofficially counted school districts in at least 12 states that have closed for one day or longer as a result of flu outbreaks. They are: Alabama, Arkansas, Idaho, Illinois, Kansas, Michigan, North Carolina, Ohio, Oklahoma, Tennessee, Texas and Virginia. Private schools have also closed in additional states, including in California, Florida, New Jersey, New York, Louisiana and West Virginia.

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The H1N1 virus strain is the most widely confirmed influenza A strain this season, however H3 viruses are dominating in the southeastern United States, the CDC reported Friday. Last year, the H3N2 strain, which is known to cause more severe illness, dominated.

Influenza B strain viruses, which lead to the same flu symptoms as A strain viruses, are also circulating, as usual, this season.

The most important response to seasonal flu, according to the CDC, is for everyone age 6 months or older to get vaccinated against the flu. As long as flu is circulating in the area where you live, it is not too late to get vaccinated. People over age 65, children under age 2 and individuals with medical conditions should also get a pneumococcal vaccination to prevent pneumonia, according to the CDC.

Overall, the effectiveness of last year’s flu shot was estimated to be 40 percent, meaning getting vaccinated reduced an individual’s risk of seeking medical care by 40 percent.

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Dr. William Schaffner, medical director for the National Foundation for Infectious Diseases, said that those who get the flu after receiving a vaccine are less likely to require hospitalization and they’re less likely to die.

“The vaccine is not perfect,” said Schaffner. “But give the vaccine credit for softening the blow.”

(©Copyright 2019 CBS Broadcasting Inc. All Rights Reserved.The-CNN-Wire™ & © 2019 Cable News Network, Inc., a Time Warner Company contributed to this report.)