Lawrence Drew, MD, PhD, director of the clinical virology laboratory at UCSF, answered some questions related to an unusual swine flu that has infected and killed people in Mexico. Swine flu also has infected 40 people in the United States and other countries. Q. What is unusual about this virus? A. It has been around, but it has acquired additional genetic information that is allowing it to be transmitted from human to human. Previously, this illness would have been due to exposure to swine. But in Mexico, it has been affecting urban dwellers and appears to be spreading from person to person. That’s a whole new development for this type of virus. That’s rare. Q. How similar is the Mexican swine flu virus that has killed healthy young people in Mexico to the virus that has infected individuals in the United States, who have recovered? What are the differences, and how might they account for differences in the effects of the virus? A. There’s a lot of study going on to determine whether they are the same. Both are swine, and they appear to be the same. The differences – that gets speculative. Perhaps, even though it is spread from human to human, it may not be that lethal a virus. Many times, a flu virus starts an illness, but it may be superseded by bacterial infection. I don’t know the circumstances of the treatment of the cases in Mexico versus here in the US. There is an oral antiflu agent called Tamiflu. Perhaps the kids in the US received flu treatment and the individuals infected in Mexico did not. Or perhaps the US cases received antibiotics for bacterial infections, and the Mexican cases did not. Or finally, it may be that the Amerian cases were in children who had received a flu vaccine this year that didn’t fully protect them, but gave them a little bit of protection, and the Mexican cases had not. Swine flu is an H1N1 virus, and our vaccine contained an H1N1 representative – not the swine, but a cousin, if you will, to the swine virus. There may have been some protection, but not complete protection. Q. Is it possible for a flu virus that spreads from human to human and that is as virulent as the deadly Mexican virus to actually become less virulent or less transmissible over time, without necessarily causing a pandemic? A. It’s not going to become less virulent once it’s acquired this genetic information. But I believe it is unlikely to become a pandemic, because it is an H1N1. And even though it is not identical to the H1N1 we have been exposed to over the last 30 or 40 years, it is somewhat similar. We have had an exposure that I believe will limit the likelihood of a pandemic. Q. As a sentinel lab, what is UCSF doing differently than it was last week? A. We’re doing the same testing we usually do. We can’t make a separation between swine flu and another A-type influenza virus. We believe we are at the end of the regular flu outbreak for the year. The cases have been tapering off. If we got a bunch of cases now, that would be a surprise. If that happened, depending on the population affected, that would alert us that it might be the newer virus. Q. Does it make sense to develop a vaccine for this flu? A. Well, this strain is different. If you wanted comparable protection, you would need to develop a vaccine that contained this H1N1, perhaps in addition to the strain we are exposed to during a yearly outbreak. But the more you include, the more diluted the antigens become. Typically, the vaccine includes antigens from two A-type influenzas – an H1N1 strain and an H3N2 strain – together with one B-type influenza representative. The current vaccine has these three components. Could it have a fourth? I would think so, and that would be needed if this is going to become a major issue. Q. Will people with flu still need to obtain prescriptions for antiflu medications from their doctors, just as they normally would? A. Yes, you will still need a prescription.