How Does the Flu Vaccine Work?

Author: Harpreet Singh, MD
Specialty: Family Medicine

Each year, between 291,000 and 646,000 people worldwide die from the flu and flu-related respiratory illnesses. When accounting for how the flu can cause or exacerbate serious and sometimes fatal conditions like cardiovascular disease or diabetes, that number could be upwards of a million.

That’s why fighting the flu is a global issue – and getting your yearly flu shot is the first and best defense.

What is the flu?

While we tend to refer to it generically as “the flu”, it’s actually four distinct genera of Influenzavirus that are then further divided by strain.

Type A flu virus is the type we associate with flu pandemics, commonly infecting humans, other mammals and birds. You may recall outbreaks of H1N1 swine flu and H5N1 bird flu; both are strains of Influenzavirus A.

Type B flu virus, which can be found in both human and seal populations, is a less common genera that mainly affects young children. Type C flu virus tends to be milder (similar in severity to a common cold) and non-epidemic.

Type D flu virus can affect some animal populations, but does not affect humans.

Why Do I Need a Shot Every Year?

Typically, there are only a few strains of influenza that circulate each year. However, viruses like the flu can mutate quickly, which means new strains of the flu virus are constantly evolving.

That’s why, every February, the World Health Organization (WHO) uses advanced modeling and population data to assess which strains of the flu have the greatest pandemic potential for the Northern Hemisphere. Manufacturers then produce vaccines based on these recommendations – which usually protect against 2 strains of Type A flu virus as well as 1-2 strains of Type B. Because the dominant strains change from year-to-year, so must the flu vaccine.

Can I Get the Flu from the Flu Vaccine?

No, you can’t get the flu from a flu shot. Unfortunately, this is a common misconception that dissuades some from getting their annual vaccination.

Vaccines do contain a viral component that helps your immune system create antibodies against active strains. However, the viral component of the shot is dead, meaning it can’t cause infection, and nasal spray vaccines contain a “live attenuated” virus, meaning it’s weakened to the point that it’s unable to replicate in average body heat.

While you cannot get the flu from the flu shot, it is still possible to get sick after being vaccinated. Common reasons for this include:

Bad Timing: After being vaccinated, it takes your body about two weeks to build up enough antibodies to fight off the full-fledge flu virus. Within that window, unfortunately, it’s still possible to get sick with the flu.
Wrong Strain: Each year, the WHO makes the best possible prediction of what strains of the flu will be most prevalent. As we saw with the 2017-2018 flu season, sometimes those predictions are wrong. In which case, even with the flu shot, you won’t be immune to the dominant strain.
Misdiagnosis: Because their symptoms are so similar, there’s a good chance that the “flu” a vaccinated person gets is actually just a really bad cold. While it may not make you feel better while sick, the common cold is nowhere near as dangerous as the flu.

Who Should and Shouldn’t Get Vaccinated?

The CDC recommends that all people aged 6 months and older receive an annual flu vaccine, with few exceptions. Those who should not receive the vaccine, include:

Children under 6 months of age.
People with severe allergies to ingredients in the vaccine, which can include gelatin, antibiotics, eggs and other ingredients.

Is it Too Late to Get Vaccinated?

No, it’s not too late.

Ideally, one would receive the flu vaccine in enough time to build up immunity before the flu hits your community. But flu season can be unpredictable. If you are not currently experiencing flu-like symptoms, you should still get your flu shot.

If you’re in the Tri-City area, you can contact your primary care provider or call Washington Hospital Urgent Care at 510.791.2273 to schedule your vaccination. Or, you can visit the California Department of Public Health to search for low- or no-cost vaccination options near you.

Posted November, 2019

About Harpreet Singh, MD
Harpreet Singh, MD, is a board-certified family medicine physician. Dr. Singh, who joined Washington Township Medical Foundation in 2019, was inspired to practice family medicine by his desire to build long-lasting relationships and provide a full spectrum of care for his patients. “I want to address not only my patients’ medical health, but also their psycho-social health,” he explained.

Practicing medicine at Washington Township Medical Foundation is a homecoming for Dr. Singh, who grew up in Fremont, where his parents still live.

“At Washington Township Medical Foundation, I have an opportunity to help my patients to a better tomorrow,” Singh said. “We want them to make healthy lifestyle choices, be inspired to achieve their goals, pursue higher education, and stay positive and persistent.”

Dr. Singh received a Bachelor of Science degree in biomedical engineering from the University of California, Davis. He then studied medicine at St. George’s University School of Medicine, both in the U.K. and in Grenada, West Indies, and participated in several clinical clerkships in the U.S. He has been an associate physician at Santa Clara Valley Medical Center in Santa Clara, and at U.S. HealthWorks Medical Group in Union City.

In addition to providing health care to the community, Dr. Singh is passionate about improving the overall quality of life for its residents, especially in terms of literacy. He is active in fundraising events, such as the Run for Health, where the funds are used to purchase books for children, as well as discussing literacy with his patients’ parents.

Dr. Singh’s interests also include reading, hiking, basketball, music and cooking. He and his wife look forward to one day starting a family. “This is a wonderful community in which to raise a family,” said Singh, whose expertise has been certified by the American Board of Family Medicine. “The diversity here, and essentially the feeling of home, are very important to us.”