By Kasra Zarei
The worst season of the year has arrived, making its stamp with coughs, runny noses, doctor visits, and absences in work and school.
The flu season has started, with the peak months of flu activity approaching around mid-winter.
From an individual standpoint, receiving a flu vaccine is the first and best way to prevent the flu from spreading, but a majority of Americans still do not get vaccines every year. Understanding the flu vaccine is a complicated task and a subject that is filled with widely held questions and misconceptions.
The University of Iowa is home to a team of infectious-disease specialists and professionals who provide preventative care and information for everyone on campus, including answers to the million-dollar question: When is the best time to get a flu shot?
“The timing of influenza vaccine is based upon the usual timing of annual influenza epidemics, which doesn’t occur until at least October,” said Daniel Diekema, UI clinical professor of internal medicine and infectious diseases.
It takes two weeks for the vaccine to become fully effective, so it is best to get the flu shot at least two weeks before the earliest time the flu season is expected to begin.
While it’s not possible to predict what the flu season will be like in terms of timing and length, historical records suggest that the flu season does not begin before October.
“It takes two weeks to develop protection after you receive the vaccine. So if the flu season comes early, and you are vaccinated after October, you may get the flu before the vaccine kicks in,” said Michael Edmond, a UI clinical professor of internal medicine and infectious diseases.
Regardless of the best time to get the shot, the flu vaccine isn’t always effective for everybody, and its effectiveness is influenced by several factors, said Lisa James, associate director for clinical outreach at UI Student Health & Wellness.
“Getting good protection by getting a flu vaccine depends on the age and health status of the individual, and having a good match between the influenza strains in the vaccine with the circulating virus,” James said.
Humans have a poorer immune response as they age, which is why higher-dose flu vaccines are sometimes recommended for elderly patients.
Vaccines allow a person to develop immunity to the flu by imitating an infection, serving as a “training course” for the body’s immune system. Each year, the flu virus mutates, so each year, a new vaccine is developed to retrain the body’s immune system.
Furthermore, the general effectiveness of the flu vaccine varies from year to year based upon how closely the vaccine strain matches the circulating strain.
“Because the vaccine strains have to be selected months in advance of the flu season to give time for the vaccine to be manufactured, there is some guesswork involved in choosing strains,” Diekema said.
Sometimes the guess is not correct.
“In a mismatch year, even with vaccination, there are influenza viruses that can still make you ill,” James said.
The overall efficacy of the flu vaccine is estimated to be between 50 and 60 percent.
“That might not seem like good odds for some students, but the vaccine is something they can do to take action for their personal health but also for their fellow students, teachers, family, and community,” James said.
Diekema said one major importance of the flu vaccine is reducing the chance of severe complications.
“The flu vaccine seems to be better at reducing the complications of influenza that require hospitalization than in reducing overall infection rates,” he said.
Although recent studies show that getting vaccinated reduces the risk of flu illness by only 50-to-60 percent, one of the biggest myths about getting the flu vaccine is that they can make you sick.
“Since it takes two weeks for full immunity to be conferred from the shot, if a student comes down with another viral illness in that time frame, they often blame the flu shot,” James said.
Beyond the limited effectiveness, many vaccines have reduced protective effects over time, as antibody levels gradually decline after exposure to a virus or a virus-vaccine
“Some immunizations do not produce long-lasting immunity, and influenza is one of those,” Edmond said. “It’s not one of our best vaccines, but [it is] still worth getting every year.”
Unlike some other vaccinations, the influenza shot has a bigger problem when it comes to long-lasting immunity.
“The target of influenza vaccines are parts of the virus that change over time, and can change quite rapidly,” Diekema said. “So the vaccine is designed to produce antibodies to a strain of virus that, by the time the season rolls around, may already be slightly different.”
The flu shot may be naturally imperfect, but it is still one of the best ways to prevent influenza, along with frequent, thorough hand washing, covering coughs and sneezes with tissues or sleeves, and staying home when sick.
