Flu Vaccine Effectiveness: How Well Do Flu Shots Work?

The flu vaccine is not 100% effective. In fact, the overall effectiveness hovers around 40 to 60%. You may find yourself wondering why bother getting it at all?

Like the COVID vaccine, a flu shot does not always guarantee protection from infection. But it does prevent millions of flu cases each year. And if you do catch the flu, the vaccine significantly reduces your chances of being hospitalized, going to the ICU, or losing your life.

Why should I get the flu vaccine if it’s not 100% effective?

Up to sixty percent effectiveness may not seem like an impressive number. But the flu is so widespread, this still translates to:

  • 6,300 deaths prevented
  • 58,000 hospitalizations avoided
  • 3.69 million doctor visits averted
  • 7.52 million fewer flu infections

CDC data, 2018-2019 flu season

Vaccination is especially important for Filipinos. Influenza and pneumonia (a frequent complication of the flu) account for 10% of all deaths in the Philippines. Getting the flu vaccine every year can help reduce this statistic.

Why is the flu vaccine more effective in some years than others?

The influenza virus is constantly changing. New anti-flu vaccines are released every year to keep up with the rapidly evolving virus. The problem is that it takes about six months to produce enough flu vaccine for the entire planet. So, scientists have to create the vaccine many months before flu season begins.

How do they predict the flu strains that will be in circulation? Researchers gather data from 142 national influenza centers across the globe for their forecasts. Sometimes the predictions are accurate and vaccine efficacy is high. But the reverse is also true–some years the vaccine is not a good match. This is why you see a range of flu vaccine effectiveness each year.

How long is the flu vaccine effective?

The flu vaccine is effective for around six months. Efficacy is at its highest two weeks after you’ve been vaccinated. Then, effectiveness begins to decline steadily. Studies show that vaccine efficacy goes down by about 10% each month. This is still sufficient to cover most people for the flu season. However, people with weakened immune systems may benefit from getting two shots each year or getting a high-dose vaccine.

When is the most effective time to receive a flu shot?

Because vaccine efficacy wanes, it’s important to time your shot right. If you get it too early, you’ll have less protection when the flu season is at its peak. You also want to avoid waiting too long to get your jab, so you are protected before the start of the Philippines’ flu season. That’s why the Philippines DOH advises getting your shot ahead of the flu season, between February and June. If you happen to miss this period, it is still advisable to get your shot because less protection is better than none.

Is one type of flu vaccine more effective than another?

There are two distinct types of flu vaccines–the trivalent vaccine and the quadrivalent vaccine. Both will help protect you from the flu. But which one is more effective? The trivalent flu vaccine offers protection against 3 flu strains, while the quadrivalent vaccine protects against four strains.

The CDC advises everyone above six months to get the flu vaccine annually, regardless of type. However, experts agree that the quadrivalent shot offers broader protection because it covers more flu strains.

How effective are flu vaccines in older adults?

Our immune system becomes weaker as we age. This means the flu vaccine is somewhat less effective for seniors.

However, it is still important for the elderly to get vaccinated. In the Philippines, about 2 out of 3 people who die from influenza are 60 years and older. Seniors can counteract their weaker immune response by receiving two flu jabs or by getting a high-dose vaccine, like Fluzone.

How effective are flu vaccines in children?

The flu vaccine is somewhat less effective in children below 24 months because their immune system is still developing.

However, if your child contracts the flu, vaccination can prevent many life-threatening complications. A study conducted by CDC established that the flu vaccine reduced the risk of being admitted to the pediatric intensive care unit (ICU), needing CPR, and flu deaths by up to 76%. For this reason, the CDC recommends every child over 6 months get the anti-flu vaccine.

How does the CDC measure how effective the vaccine is?

The CDC measures the effectiveness of the flu vaccine in two ways: randomized controlled trials (RCTs) and observational studies.

During RCTs, the CDC gets volunteers to participate in efficacy studies. Some people are given the flu vaccine and others receive a placebo. The two groups are monitored to see which one has higher rates of infection and complications. This helps the CDC measure vaccine efficacy in a controlled, laboratory setting.

In observational studies, the CDC looks at how effective the vaccine is in the general public. They measure key outcomes, such as the number of flu cases, hospitalization rates, ICU admissions, and deaths. This helps determine how well the vaccine works in a real-world setting.

Flu vaccination is the best prevention

Several factors can reduce vaccine effectiveness, from inaccurate predictions to the timing of your shot. But an imperfect vaccine is still better than none. Even in a year when the vaccine is less effective, it can save thousands of lives and prevent serious complications. Flu vaccination remains the most effective way to prevent you and your family from the flu.