Nightly News   |  February 10, 2013

U.S. struggling to contain whooping cough

A new strain of whooping cough recently discovered in the United States may not be protected by today’s vaccine. NBC’s Nancy Snyderman reports.

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>>> we're back with health news, and concern about a growing outbreak of whooping cough . it's a bacterial infection that can be fatal to very young children, while it was almost gone at one time, cases are now on the rise. nbc's chief medical editor dr. nancy snyderman has more on this tonight.

>> reporter: 2012 was america's worst year for whooping cough in more than six decades.

>> there's a tremendous outbreak of whooping cough across the united states right now.

>> reporter: as scientists try to figure out how to better prevent infection, they're also looking at a new strain recently discovered here in the united states that may not be protected by today's vaccine. the first vaccine became available in the 1940s , sparking a dramatic drop in cases that continued for decades. but it had some side effects , including the risk of brain danger. so in 1991 , a safer, but slightly less effective series of shots was introduced. since then, cases have shot up. more than 1,400%, from fewer than 3,000 cases in 1991 to more than 40,000 last year. while scientists say the new strain is responsible for some cases, recent outbreaks are mainly due to the vaccine wearing off over time which leaves people less protected. the decline occurs even in those who got the original and more potent whooping cough vaccine. now doctors are still measuring the staying power of the new vaccine, which they say fades much faster, though it's unclear just how fast. the cdc recently changed its guidelines to include whooping cough booster shots for pregnant women . it now recommends one during every pregnancy, in order to give babies who are among the most vulnerable protection at birth.

>> by vaccinating mother, the mother will then pass her immunity to the baby, and when the baby is born, that baby will have protection.

>> reporter: as researchers try to improve protection against highly contagious diseases, they say the best thing people can do is remain up-to-date with immunizations and get those booster shots . dr. nancy snyderman , nbc news, new york.