Vaccine Effectiveness for Influenza

Flu vaccines have been around since the early 20th century and continue to grow in popularity during flu season. But how effective are they exactly? Each year, the CDC conducts studies to determine how well the influenza vaccine protects against the flu. Vaccine effectiveness can vary depending on a variety of factors, but it was generally found that the vaccine reduces the risk of the flu by 40-60% throughout the overall population. Sometimes, the flu vaccine does not match with circulating influenza viruses, which makes it less effective. Even when there is a match, other factors like pre-existing health conditions of individuals getting the vaccine limits effectiveness. It is also important to understand that the flu vaccine does not protect against other viruses that cause flu-like symptoms.

Overall, flu vaccines protect better against influenza B (H1N1) viruses, as compared to influenza A (H3N2) viruses. Influenza A and B are the two different types of influenza viruses present during the flu season. Influenza A (H1N1) viruses are the only ones known to cause global flu pandemics. Trivalent flu vaccines are formulated to protect against three flu viruses while quadrivalent vaccines protect against four. Overall, the two have similar symptoms, hospitalization rates, and death rates. Despite this, there are still numerous benefits to getting the flu vaccine that outweigh the disadvantages. For example, many studies have concluded that flu vaccines cut the risk of influenza-related hospitalization even after infection.

Scientists and doctors are looking for ways to improve the vaccine by making it more efficient and keeping it up to date with evolving situations. The two strains of Influenza, A and B, further branch out into mutated versions as the strain continues to evolve. Potential solutions include producing the annual vaccine more quickly. Until 2013, all flu vaccines were made by growing samples of the viruses in fertilized chicken eggs, which was an inefficient and time-consuming process. Cell-based vaccines, where samples of the virus are grown in cultured animal cells, are a better alternative, as this method takes less time and is more innovative. Another potential solution is developing a universal flu vaccine that reduces the need for scientists to develop a new version of the vaccine each year. Several of these methods are undergoing clinical trials, and three have even reached phase III, meaning that they are being tested on thousands of people to make sure they work and are safe. These are all methods that could potentially be used in the future to boost the effectiveness of the influenza vaccine and reduce cases overall.

In order to measure the effectiveness of the flu vaccine, the CDC uses mathematical calculations to release a report each year. These steps take into account several factors, such as hospitalizations by specific demographics and the number of cases compared to previous years. The U.S. Flu Vaccine Effectiveness Network’s sites use a highly accurate lab test called PCR (polymerase chain reaction) to test for flu viruses in the respiratory system of its specimen. This and combined studies compare the frequency of vaccination among patients who test positive for influenza with vaccination in a control group without influenza. This past flu season, the U.S. Influenza VE Network collected data from 4112 children and adults who had contracted the flu from October 2019 to January 2020 and found that the vaccine had an overall 45% effectiveness rate.

Each year, vaccines are developed to protect against 3-4 strains of influenza. The World Health Organization (WHO) identifies those strains for the Northern Hemisphere by collecting information on viruses circulating in the Southern Hemisphere in the previous six months. Sometimes, the viral strains that end up in North America and the Northern Hemisphere do not match the strains that the vaccine is supposed to protect against. For future vaccines, the FDA recommends that they contain a type of H1N1, H3N2, and two versions of type B.

In terms of what you can do to protect yourself from the flu and other viruses, getting vaccinated is an important precautionary measure. Cleaning and disinfecting surfaces, as well as keeping your hands clean are crucial to reducing the spread of many viruses, even beyond the flu. The flu season typically lasts from the start of fall to late winter, but activity can last as late as May. It takes nearly 2 weeks after the vaccine is administered for it to be effective, so getting the vaccine at the start of flu season is recommended by doctors. Even though the vaccine does not prevent the flu in all cases, it reduces the severity and duration of the illness.

Works Cited

1. Averett, N. (2020). The flu shot is 46% effective for this year's 2020 flu season. Insider. https://www.insider.com/how-effective-is-the-flu-shot

2. Barber, K. (2020). How the flu vaccine is made. Insider. from https://www.insider.com/how-is-the-flu-vaccine-made

3. CDC. (2019). Flu vaccines work. https://www.cdc.gov/flu/vaccines-work/index.html

4. CDC. (2020). Vaccine effectiveness: How well do the flu vaccines work? https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm

5. Koenig, D. (2020). How effective is the flu vaccine? WebMD. https://www.webmd.com/lung/news/20200902/how-effective-is-the-flu-vaccine