During a lecture to his BIOL 0530: “Principles of Immunology” students last semester, Richard Bungiro, lecturer in biology, invited workers from Health Services on stage to inject him with this year’s influenza vaccine.
“I guess you could call it a publicity stunt,” he said.
After class, about 70 percent of Bungiro’s students followed suit and rolled up their shirtsleeves to be vaccinated against the flu.
With the flu season off to an earlier-than-usual start this year, the vaccine is “far from perfect, but still the best tool we have to prevent the flu,” said Tom Frieden, director of the Centers for Disease Control and Prevention during a Jan. 11 media conference call.
This year, the flu has resulted in 20 pediatric deaths, and 24 states are now reporting a high level of influenza-like illness, Frieden said at the conference.
The flu season is hitting the nation particularly hard this winter because the predominant circulating strain, H3N2, causes the most severe kind of flu, said Aurora Pop-Vicas, assistant professor of medicine.
“We’ve had a lot more hospitalizations this year from influenza-like illnesses and more incidences of laboratory-confirmed influenza,” Pop-Vicas said. Previous seasons have yielded few lab-confirmed flu cases in adults and the elderly, but Memorial Hospital of Rhode Island has had close to 40 admissions in one month this year, she said.
As of mid-November, about 37 percent of Americans had been vaccinated, which is on par with last year, said Joe Bresee, chief of epidemiology and prevention with the CDC’s influenza division, during the conference call. Still, the CDC hopes that number will rise to about 50 percent, Bresee said. Approximately 130 million doses of flu vaccine have been delivered, he added.
This year’s vaccine is 62 percent effective, meaning vaccinated individuals are 62 percent less likely to get a case of the flu that requires them to go to a doctor, Frieden said. This number is comparable to flu vaccine effectiveness rates from past years but is below the 90 percent efficacy of most childhood vaccines, he said.
Flu vaccines come in two forms — flu shots, which contain a version of the influenza virus that has been inactivated, and nasal sprays, which contain a weakened version of the live virus, according to the CDC.
Once injected into an individual, the vaccine causes the body to make antibodies, said Daniel Weinreich, assistant professor of ecology and evolutionary biology. This is the body’s way of “remembering” the foreign virus, so the next time the individual encounters that virus strain, it can identify it and mount a defense much more quickly, he said.
“The vaccine mimics infection,” Weinreich said. “Your body is ready because it has had the exercise and the training.” Those who do not receive the vaccine have a longer lag time before their body recognizes and attacks the flu virus, he said.
“The pick of vaccine strains was as good as it could have been this year,” Frieden said in the conference call. “About 90 percent of all the strains circulating are included in the vaccine,” he said.
But there is one strain, which accounts for about 10 percent of the circulating flu viruses, that the vaccine is not effective against. There is no evidence that this strain is more or less severe than other strains, Bresee said.
Creating an effective vaccine is difficult for scientists because the flu virus mutates at such a rapid rate, Bungiro said.
The virus mutates in two ways, Bungiro said. The first way is through antigenic drift — genetic variation that occurs in the virus as it replicates. This form of mutation takes place gradually, but “over time changes the virus enough that antibodies that you made last year might not be as effective,” Bungiro said.
The second mechanism of mutation, known as antigenic shift, is harder to predict, he said. For this sort of mutation to occur, two different strains of the virus must infect a single organism. Inside the host, the virus strains swap genetic material, resulting in a new form of the influenza virus, Bungiro said.
“The only thing predictable about the flu is that it’s unpredictable,” Frieden said in the conference call.
The World Health Organization and the CDC begin work on the vaccine one year in advance, Bungiro said, meaning the 2013-2014 vaccine is already being developed.
The vaccine can include three strains of flu, so scientists predict which three strains will be the most prevalent during the following year’s flu season. Development of the vaccine amounts to an “educated guess,” Bungiro added.
“You get one shot, but it’s actually three vaccines,” Weinreich said.
To increase the effectiveness of the vaccine, scientists are currently developing quadrivalent vaccines, which could include four strains of the virus, Frieden said.
“There’s a lot of research going on towards improving influenza vaccines by novel approaches like looking at different proteins on the surface of the vaccine,” Bresee said. He noted the quadrivalent vaccine could be used by the CDC as soon as next year.
“We tend to think of influenza as one entity because the experience of the illness is very similar. But on a genetic and molecular level it turns out that there are diverse strains of flu,” Weinreich said.
Because the immune systems of young people are stronger than those of the elderly, the vaccine tends to be more effective in younger recipients, Pop-Vicas said. This is a public health challenge because the people who are most susceptible to severe flu — the frail, the elderly and people who have had cancer — are also the least likely to benefit from the vaccine, Frieden said.
Despite the flu virus’ propensity to mutate, the vaccine is an effective measure against the flu, Weinreich said. While the vaccine will help prevent infection in individuals, perhaps a greater benefit is that it shuts down the widespread transmission process, he said.
“There’s a certain population effect,” Weinreich said, “and the fewer people who are infected, the harder it is for the virus to get traction in the population.”