-LRB- Health.com -RRB- -- An analysis of the sickest swine flu patients in Australia , Canada , Mexico , and New Zealand suggests that relatively healthy adolescents and young adults are among the most likely to get very sick after an H1N1 infection , a pattern similar to that seen in the 1918 influenza pandemic . The most important message is that children should get the H1N1 vaccination , Dr. Neil Schachter said . Almost all critically ill patients in the studies were sick for only a few days before rapidly progressing to more severe symptoms and respiratory failure , which required treatment with a breathing machine , according to three studies published in the Journal of the American Medical Association . The mortality rate ranged from 14.3 percent to 41.4 percent , depending on the country . The findings may help shine some light on what the 2009 H1N1 flu season may bring , and who may be hit the hardest by the swine flu during the next few months . `` These studies are telling us that young people are at risk for bad complications of H1N1 and under usual circumstances , -LSB- seasonal -RSB- flu does not cause acute respiratory failure in younger people , '' says Dr. Neil Schachter , the medical director of the respiratory care department at Mount Sinai Medical Center , in New York City , and the author of The Good Doctor 's Guide to Colds and Flu . The analysis of cases in Australia and New Zealand looked at people who developed severe acute respiratory distress syndrome -LRB- a condition in which the lungs fill with fluid -RRB- and were put on a life-support system known as extracorporeal membrane oxygenation -LRB- ECMO -RRB- . This artificial heart and lung machine system , which puts oxygen into the blood and then carries this blood to the body tissues , is considered risky and expensive ; as a result , it is not readily available in every hospital . The mortality rate was 21 percent for these patients , although it may have been higher without this treatment , the authors say . Health.com : 8 ways swine flu is changing society `` These studies provide important signals about what clinicians and hospitals may confront in the coming months , '' Dr. Douglas B. White , and Dr. Derek C. Angus , of the University of Pittsburgh School of Medicine , write in an editorial accompanying the new studies . In young , healthy patients , H1N1 can quickly cause respiratory failure that ca n't necessarily be reversed with mechanical ventilation , although such patients are not currently a priority group for H1N1 vaccination , they note . In the Canadian study , about 30 percent to 40 percent of the patients had lung disease , were obese , or had high blood pressure , a history of smoking , or diabetes . Overall , 14.3 percent of 168 critically ill people with confirmed or suspected H1N1 died within 28 days . The mortality rate in the Mexican study was strikingly higher . In Mexico City , where the H1N1 pandemic was first reported , 41.4 percent of 58 critically ill people died within 60 days of developing the flu . Health.com : 10 best big cities for people with asthma Those people who died from H1N1 got sicker earlier in the course of their illness , had extremely low levels of oxygen in their blood , and had multiple organ failure . Their average age was 44 years old , and 54 of 58 patients needed mechanical ventilation . Other signs of more severe H1N1 included fever and severe trouble breathing . Health.com : 10 ways you put yourself at risk for swine flu -LRB- without realizing it ! -RRB- In the Canadian study -LRB- in which the average age was 21.4 -RRB- , the critically ill tended to be hospitalized within four days of developing flu symptoms , and there was about a one-day lapse between hospital admission to intensive care unit -LRB- ICU -RRB- admission . As in the Mexico City study , younger patients with low blood oxygen and multisystem organ failure were hardest hit . What 's more , the critically ill tended to require mechanical ventilation and rescue therapies to aid in breathing . Health.com : 8 causes of chronic cough In both countries , the H1N1 outbreak lasted about three months . `` It is not clear of hospitals ' need to invest in this ECMO technology because this has not proven very successful in other respiratory illnesses , '' says Schachter . `` We do know that treating H1N1 with antivirals such as Tamiflu -LRB- oseltamivir -RRB- and Relenza -LRB- zanamivir -RRB- did help improve mortality . '' The most important message is that children should get the H1N1 vaccination , which is safe , he says . `` The technology for making swine flu vaccine is no different than that used to make the regular flu vaccine , so in principle , there should be no differences in terms of safety , '' he explains . `` Recent surveys have shown that Americans are iffy about whether they will let their children receive this novel vaccine . '' Dr. James B. McAuley , the director of Pediatric Infectious Diseases at the Rush University Medical Center , in Chicago , Illinois , notes that the studies focused on the sickest of the sick patients . Health.com : 7 surprising triggers of lung trouble `` The mortality rate can be high for a small subset of people , but the overall death rate is closer to seasonal flu than the severe acute respiratory syndrome -LRB- SARS -RRB- outbreak of 2003 , '' he says . `` This is a serious flu and there is mortality , but it is about the same as with the seasonal flu -- maybe a little worse . '' As to why younger people seem to be hit hardest , the current school of thought is that perhaps a similar virus circulated 50 or 60 years ago , so older people could have immunity to H1N1 . McAuley 's advice ? `` Definitely get the vaccine , '' he says . -LRB- He says his own children have already received the H1N1 vaccination . -RRB- The editorialists write that the burden is on the public health system to heed the warnings in the new studies and prepare for the coming flu season : `` Any deaths from 2009 influenza A -LRB- H1N1 -RRB- will be regrettable , but those that result from insufficient planning and inadequate preparation will be especially tragic . '' Such planning should include widespread availability of antivirals , antibiotics , and mechanical ventilation systems . Enter to win a monthly Room Makeover Giveaway from MyHomeIdeas.com