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H1N1 (Swine Flu): Canadian Vaccine Study Refuted and Surgical Masks and N95s provide Similar Protection

October 6, 2009

Yesterday two reports/studies were released addressing some pressing concerns.  On September 23 a unpublished and unpeer reviewed study was released in Canada raising concerns about whether it’s a good idea to get a seasonal flu shot this fall. The data appeared to suggest that people who got a seasonal flu shot last year are about twice as likely to catch swine flu as people who didn’t.  WHO was not convinced….  The second study was just released in the Journal of American Medical Association (JAMA) suggesting that in “average” medical situations (and hence in community settings) a surgical mask was comparable to an N95 mask. This contradicts the IOM study released last month. Confused?  Read on…

WHO: NO NEED TO CHANGE VACCINE POLICY BASED ON CANADIAN FLU SHOT DATA

International influenza vaccine experts are apparently not convinced that Canadian researchers have found a true link between getting a seasonal flu shot and catching swine flu. The consensus that emerged from a WHO teleconference Friday on the controversial data seemed to be that the Canadian findings are likely due to some confounding factor or factors in the data themselves and may not reflect a real increased risk, according to a WHO official who helped pull together the meeting.

 "From a WHO point of view, the fact that the findings are not replicated in other countries I think is reassuring for us that this is an outlier, if you like, the unexpected findings that are coming out of Canada," said David Wood, coordinator of the quality, safety and standards team of WHO's department of immunization, vaccines and biologicals. "Most people are still looking at this as some sort of undetected confounding in the data, that for some reason is giving the results that are there."

"From a WHO point of view, the fact that the findings are not replicated in other countries I think is reassuring for us that this is an outlier, if you like, the unexpected findings that are coming out of Canada," said David Wood, coordinator of the quality, safety and standards team of WHO's department of immunization, vaccines and biologicals. "Most people are still looking at this as some sort of undetected confounding in the data, that for some reason is giving the results that are there."

In an interview from Geneva, Wood was diplomatic. But when pressed, he did admit most experts on the call didn’t seem to believe that the unpublished study, based on data from British Columbia, Quebec and Ontario, had found a true link between getting a seasonal flu vaccine and having an increased risk of coming down with a mild case of H1N1 flu. Because it is an unexpected finding. That’s the way people tend to think.” The work, which is said to be being considered for publication by a medical journal, contributed to decisions by most provinces and territories to stagger or delay their seasonal flu shot efforts this fall.

Instead of launching full-fledged seasonal flu vaccine programs in October, most have announced they will offer seasonal shots in October only to seniors – who aren’t currently at high risk from the pandemic H1N1 virus – and residents of long-term care facilities. After pandemic vaccination efforts are completed, most of those provinces plan to offer seasonal vaccine more broadly.

The Canadian findings, which are reportedly mirrored in data from Manitoba as well, suggest that people who got a flu shot last fall were twice as likely as people who didn’t to contract swine flu. But the association, if it is real, is to mild disease. There is no evidence that people who got seasonal flu shots are more prone to develop severe illness if they catch the new H1N1 virus.

Scientists from the United States, Britain and Australia have looked at their data but didn’t see the same effect. A number of scientists have speculated that the Canadian data may have some built-in confounders – factors that can produce false results. For instance, if people who get flu shots are also more likely to seek a diagnosis of swine flu if they get sick, that could make it seem like more of them got the illness when in fact what happened is that more of their illnesses were recorded. But if the Canadian results are due to some statistical flaws or selection biases, no one on the 4 1/2-hour teleconference was able to put a finger on what exactly the problem is, Wood acknowledged. And he admitted there may not be a satisfactory answer to that puzzle in the foreseeable future.

In the meantime, a summary of the situation will be presented to the WHO’s Strategic Advisory Group of Experts on immunization, also known as the SAGE. The group, which meets later this month, makes recommendations for the WHO on vaccination policy. Wood said he couldn’t prejudge what the committee will decide, but said for the moment it doesn’t seem like the WHO needs to ask countries to change their vaccination programs for this fall. “The fact that it’s just been seen in Canada at the moment, I don’t think that that’s going to force global policy changes,” he said.

http://www.google.com/hostednews/canadianpress/article/ALeqM5gPz7AwhAlmZF7pAyHmP0GWejWPHg

SURGICAL MASKS, N95 RESPIRATORS OFFER SIMILAR PROTECTION AGAINST INFLUENZA TRANSMISSION

Rates of laboratory-confirmed influenza were similar among health care providers who wore surgical masks compared with those who wore fit-tested N95 respirators while caring for febrile patients with respiratory illness, recently published data indicate.

Researchers from several sites in Canada and the United States randomly assigned 446 nurses at eight Ontario tertiary care hospitals to wear either a surgical mask (n=225) or an N95 respirator (n=221) between Sept. 23, 2008 and Dec. 8, 2008. During the study period, 50 nurses in the surgical mask group contracted laboratory-influenza compared with 48 in the N95 respirator group.

“Surgical masks had an estimated efficacy within 1% of N95 respirators in preventing influenza,” the researchers wrote.

“Surgical masks had an estimated efficacy within 1% of N95 respirators in preventing influenza,” the researchers wrote.

Vaccination status was similar among the two groups, with about 30% of nurses in each having received 2008-2009 trivalent inactivated influenza vaccine.

“This is a tremendous addition to our body of knowledge on this issue,” Mark E. Rupp, MD, president of the Society for Healthcare Epidemiology of America and professor of infectious diseases at the University of Nebraska Medical Center, said in an interview. “Going with a simpler, more cost-efficient surgical mask that health care workers will be more compliant with makes more sense than something that is cumbersome, uncomfortable, more costly and no more effective in routine clinical situations.”

The study findings are in accordance with SHEA’s recommendations for managing novel H1N1 influenza, which are based on the knowledge that the novel virus behaves similarly to seasonal influenza, according to Rupp, who said N95 fit-tested respirators should be reserved for procedures more likely to generate aerosols, such as bronchoscopy or intubation.

This study's findings contradict results presented at the recent ICAAC meeting that indicated that N95 masks may be more effective at preventing influenza transmission than surgical masks.

This study's findings contradict results presented at the recent ICAAC meeting that indicated that N95 masks may be more effective at preventing influenza transmission than surgical masks.

“It’s understandable that health care workers are concerned about acquisition of influenza in the work place, but quite frankly the type of respiratory protection they use is way down on the list of infection control measures that they should be emphasizing,” Rupp said. Vaccination is the most effective way to protect both patients and those in the health care community, according to Rupp, who encourages vaccination once the H1N1 vaccine becomes available.  Other important infection control strategies include prompt recognition and triage of patients with flu-like illness, promoting cough etiquette, encouraging patients to wear a mask, promoting appropriate hand hygiene and excluding sick visitors and healthcare workers.

http://jama.ama-assn.org/cgi/content/full/2009.1466

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