Is Swine Flu Dying Down or Gearing Up for a Comeback in the Fall?

The mutant strain of H1N1 flu continues to make its mark around the world. As of Monday, May 11 the World Health Organization (WHO) was reporting 4,694 laboratory confirmed cases in 30 countries, including the first in mainland China. However, as Dr. Gordon Dickinson, chief of infectious diseases at the University of Miami Miller School of Medicine and the Miami VA noted, for every confirmed case there are probably hundreds of unconfirmed cases. Based on a new analysis of confirmed H1N1 cases in Mexico and its international spread, WHO researchers estimate that by late April possibly up to 32,000 people had been infected in Mexico alone. 

With 2,618 confirmed cases across 44 states and the District of Columbia, including 94 hospitalizations and three deaths, the U.S. now surpasses Mexico as the country most affected by the outbreak. Most of the new cases in the U.S., according to Dr. Richard Besser, the CDC’s acting director, are now caused by person-to-person transmission and not a link to Mexico, as was the case when the outbreak first began. So far, the majority of the cases have been mild and the deaths linked to the virus occurred in people with multiple underlying health conditions. But Dr. Anne Schuchat, the interim deputy director at the CDC, noted that since many people who become ill don’t seek medical attention and are never tested for this particular strain of flu, “the numbers we are reporting are a minority of the actual infections that are occurring in the country.”

In Canada, health officials have confirmed 40 new cases of swine flu, bringing the total number across the country to 331. The majority of the new cases, 34, were found in Ontario, which now has had a total of 110 cases since the beginning of the outbreak. The remaining cases are scattered around the country, including two in Quebec and three in Alberta.

In Mexico, the epicenter of the outbreak, the infection toll stands at 2,059, with 56 deaths, according to Mexican Health Minister Jose Angel Cordova. Struggling for a degree of normalcy after a virtual shutdown, the country reopened businesses, government services, high schools and universities last week. On Monday, kindergartens, primary and middle schools shut down since April 24 reopened, with teachers checking students for any sign of flu symptoms. Secretary of Public Education Alonso Lujambio Irazabal urged parents not to send sick children to school. “School life will return to normal as long as the safeguards we have put in place are effective. Help us in this,” he said. As an added precaution, gym classes and ceremonies remain suspended and any students with symptoms were to be stopped at the door and sent home. “It’s very important for families to know that the disease is curable; we have enough medicine to treat any cases that arise,” said Irazabal. “As soon as we suspect we have a case we are going to offer antivirals to that person, that teacher, that student.” Six of Mexico’s 31 states put off reopening schools for another week because of local rises in the number of cases, and a seventh ordered a one-day delay.

Mexican authorities also announced a $1.06 billion business support program aimed at reviving the country’s economy. “We are not looking for magical or spectacular solutions—which would be illusory—only that businesses have the liquidity need to recover from this emergency,” said Finance Secretary Agustin Carstens. “Mexico is facing a very complicated year that combines a flu outbreak with one of the most severe global recessions in the last 60 years.”

Professor Neil Ferguson, author of a new study from the MRC Centre for Outbreak Analysis and Modelling at the Imperial College London, says the fatality rate seen in Mexico equates to around 4 in 1,000 cases, making this strain of influenza A about equal in severity to 1957 Asian flu and less severe than the deadly 1918 Spanish flu. “Our study shows that this virus is spreading just as we would expect for the early stages of a flu pandemic. So far, it has been following a very similar pattern to the flu pandemic in 1957, in terms of the proportion of people who are becoming infected and the percentage of potentially fatal cases that we are seeing,” he said. “What we're seeing is not the same as seasonal flu and there is still cause for concern—we would expect this pandemic to at least double the burden on our healthcare systems. However, this initial modelling suggests that the H1N1 virus is not as easily transmitted or as lethal as that found in the flu pandemic in 1918.”

But the CDC and other experts say it’s far too early to breathe a sigh of relief, as the new virus could continue to mutate only to return in a more virulent form in the fall. “It’s too early to say,” Dr. Ghinwa Dumyati, an associate professor of medicine, division of infectious diseases at the University of Rochester Medical Center. “At this point, it doesn’t look like it has sustained transmission, but you don’t know, in the winter, what will happen.”

Dr. Dickinson agrees. “People need to stay tuned and see what’s going on, and the medical community needs to work fast and hopefully, a vaccine will be prepared,” he added. “What bothers me is that, in 1918, the influenza emerged in the spring then sort of melted away during the summer. Then it came back as a very lethal process. This gives one pause as we see this current H1N1 epidemic spreading. The cases continue to emerge. It just hasn’t hit with a major force yet.”