The news media is full of reports of possible, probable and confirmed cases throughout the United States. The CDC updated its numbers last about two hours ago.

Indiana’s Health Department is reporting 1 case.

California reports 1 more than the CDC.

New Jersey is reporting 5 probable cases.

Neither Florida or North Carolina currently have any swine flu cases reported on their website. The New York City site continues to have only the cases from St. Francis.

The Centers for Disease Control (CDC) held a briefing this afternoon. Anne Schuchat, M.D., Interim Deputy Director for Science and Public Health Program and Daniel Jernigan, M.D., Ph.D., Medical Epidemiology, Influenza Division were the briefers.

There are 20 laboratory confirmed cases of the swine flu in the United States, from 5 states. 1 patient required hospitalization. All the patients have recovered. Human to human transmission has been confirmed. Patient ages range from 7 to 54.

All the US cases have recovered without antiviral treatment. High fever, sore throat, muscle aches, possible vomiting or diarrhea are the symptoms these patients experienced. The tested viruses are sensitive to Tamiflu and Relenza.

The interventions by the CDC and state and local governments will vary by locality. Listen to your state and local health departments for information for your area. It is important that individuals do some planning, such as what they will do if schools close.

We cannot stop this illness at the border. We cannot contain the virus. The goal is to slow transmission.

We need to prepare for the appearance of additional cases in additional states. Dr. Schuchat fears that we will see deaths in the United States from this illness.

The CDC has 12 samples from Mexico that are positive for swine flu. They also have samples that are positive for seasonal influenza. The illnesses are found in several parts of the country. CDC teams are in Mexico working with their public health authorities.

There is no vaccine for the swine flu at this time. The CDC is building a seed sample of the swine flu virus which would be given to vaccine manufacturers if the decision is made to create a vaccine. Growing the virus is the first challenge. There is new technology available that may speed that process.

The seasonal influenza vaccine component for human H1N1 initially appears to confer no immunity to the swine flu. One hypothesis is that exposure to human H1N1 may confer some immunity but there is not enough data at this time to prove or disprove this guess.

A great deal of science remains to be done. There is not enough data at this time to make very many conclusions. It is premature to suggest that the illness is different in Mexico or that it is affecting only specific age groups.

The normal disease screenings are being conducted at the border. The CDC plans to handout yellow cards to travelers giving signs and symptoms, and instructions to seek treatment if the person becomes ill. It will be up to the travelers to watch for illness and seek care.

We tolerate the “flu season” just as we once tolerated the annual “yellow fever season”. The CDC is making every effort to change our perception so that we no longer see the flu as routine.

As always, the caveat that the CDC information is up to two weeks behind when released publicly.

Influenza activity in the United States, week ending January 10, 2009

CDC:

CDC has antigenically characterized 158 influenza viruses [93 influenza A (H1), 13 influenza A (H3) and 52 influenza B viruses] collected by U.S. laboratories since October 1, 2008.

All 93 influenza A (H1) viruses are related to the influenza A (H1N1) component of the 2008-09 influenza vaccine (A/Brisbane/59/2007). All 13 influenza A (H3N2) viruses are related to the A (H3N2) vaccine component (A/Brisbane/10/2007).

Influenza B viruses currently circulating can be divided into two distinct lineages represented by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. Seventeen influenza B viruses tested belong to the B/Yamagata lineage and are related to the vaccine strain (B/Florida/04/2006). The remaining 35 viruses belong to the B/Victoria lineage and are not related to the vaccine strain. Thirty of the 35 viruses belonging to the B/Victoria lineage were from two states.

Data on antigenic characterization should be interpreted with caution given that:

1. Few U.S. isolates are available for testing because of limited influenza activity thus far.
2. The majority of viruses antigenically characterized to date come from only three states and may not be nationally representative.
3. Antigenic characterization data is based on hemagglutination inhibition (HI) testing using a panel of reference ferret antisera and results may not correlate with clinical protection against circulating viruses provided by influenza vaccination.

Annual influenza vaccination is expected to provide the best protection against those virus strains that are related to the vaccine strains, but limited to no protection may be expected when the vaccine and circulating virus strains are so different as to be from different lineages, as is seen with the two lineages of influenza B viruses.

Based on the current, limited data, this year’s flu shot would appear to be effective. The B viruses were the issue late in the season last year but the data sample is too small to allow a guess as to this year’s activity. As of this moment, it looks like we may have a good year with a lighter than normal flu outbreak.

If so, we should recognize the efforts of the CDC to have the flu vaccine widely distributed to the at-risk population, and the growing numbers of patients vaccinated for pneumonia.