It’s official — flu season has begun in Texas. Although, people can catch the flu year-round, it’s not “flu season” until more than 2.5 percent of doctor office visits are for flu-like illnesses.

In Texas, we usually cross this threshold in December. Generally, the flu peaks in February and then tapers down, reaching a baseline in April that continues until fall. However, the flu can be unpredictable. For example, the severe 2009-10 season was in full force in September and peaked in October.

The flu spreads easily between people within 6 feet of each other by coughs and sneezes so more than cheer may spread at holiday gatherings. Symptoms usually begin about two days after exposure, with the abrupt onset of fever, headache, body aches and fatigue, along with cough, sore throat and runny nose.

An uncomplicated infection lasts about a week. However, prolonged illness or permanent disability may occur if an individual develops flu-related pneumonia, kidney damage, heart attack, brain inflammation or Guillain-Barre syndrome (paralysis).

There are many different flu strains because the virus mutates at an incredible pace. This is the reason people can repeatedly catch the flu (some may even be unlucky enough to have it twice in one season). The ever-changing strains make development of a highly effective flu vaccine extremely challenging. Current vaccines protect against either three or four strains.

All vaccines contain two “A” strains (H1N1 and H3N2). Most also contain two “B” strains, but the vaccines only for seniors contain only one “B” strain. These vaccines for seniors stimulate a stronger response from an aging immune system. The tradeoff is that they cover just three strains, but that is considered fine as “A” strains circulate more than the “B” strains and infections with “A” strains are more likely to lead to hospitalization and death.

The effectiveness of the flu vaccine varies and typically works best in younger and healthier persons. The effectiveness also varies by the type of vaccine and the degree of similarity between viruses in the vaccine and those in circulation (the “match”). Sometimes vaccinated people catch the flu, but they still benefit from vaccination as the illness is less severe, reducing the likelihood of hospitalization and death.

The flu vaccine is recommended for everyone 6 months and older. After vaccination, it takes about two weeks to develop protection. Adults don’t need more than one dose per flu season, even if the season goes long. At least 75 percent of the population needs to be vaccinated to begin limiting the spread of the flu through herd immunity, which is almost double the current percentage vaccinated.

If you haven’t been vaccinated yet, it’s not too late. Flu season will continue for several more months. Vaccination helps protect you and minimizes your chance of giving the flu to your family and friends during the holiday season.

Vaccine Smarts is written by Sealy Institute for Vaccine Sciences faculty members Drs. Megan Berman, an associate professor of internal medicine, and Richard Rupp, a professor of pediatrics at the University of Texas Medical Branch. For questions about vaccines, email

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