New Year, New Flu Season: Insight on the 2019-2020 Flu Vaccine’s Effectiveness

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By Michele Yi

Every year brings the same signs of winter: the days get colder and the winds blow harder. But more importantly, winter always brings a friend we all know too well: flu season. Your day is interrupted by a sneeze, and then a cough. Next thing you know, you’re lying in bed with a 102 degree fever, feeling fatigued and nauseous. Every year, despite our best efforts to develop and administer flu vaccinations, the virus is relentless, infecting millions of people every year. Thus, understanding the efficacy of this year’s flu vaccine in fighting the seasonal flu virus could serve as a benchmark for our progress in controlling one of the most widespread illnesses to date.

The 2019-2020 flu season began in early November, marking the earliest start of the flu season since the 2009 pandemic. It began in April of 2009, when a new influenza A virus (H1N1) arose. So far, this season’s flu has infected at least 32 million people, resulting in 310,000 hospitalizations and 18,000 deaths. In addition, there were 92 influenza-associated deaths of children and teens younger than 18, which has been the largest since the 2004-2005 flu season. These numbers have not been decreasing for the past few seasons, bringing into perspective the gravity of the flu and its impact on us. However, compared to those of the past few flu seasons, this season’s flu vaccine has been more effective in terms of protection against the flu virus. According to the Centers for Disease Control and Prevention (CDC) website, the vaccine has been 50 percent effective against influenza B and 37 percent effective against influenza A, which are the viruses mainly responsible for the seasonal flu. Overall, the flu vaccine was 45 percent effective: a drastic increase from a 29 percent effectiveness of the flu vaccine during the 2018-2019 flu season.

The flu vaccine is a crucial part of keeping the flu under control every year, and the U.S. uses three different production technologies (all of which have been approved by the U.S. Food and Drug Administration) to produce millions of flu vaccines: egg-based technology, cell-based technology, and recombinant technology. Egg-based technologies use candidate vaccine viruses (CVVs), which are injected into fertilized hen eggs. The eggs are incubated in order for the viruses to replicate. Then, the virus-containing fluid inside the eggs is collected. To make inactivated flu vaccines, the viruses in the fluid are killed (or inactivated, since viruses are nonliving), and the viral antigens––the parts that trigger the immune system––are removed. For nasal spray flu vaccines, however, the CVVs are kept alive, but they are weakened (attenuated). As for cell-based technology, the CVVs are obtained from influenza viruses grown in cells and injected into cultured mammalian cells to undergo replication. Afterwards, the cell-based technology process is similar to egg-based: the virus-containing fluid is collected and cleansed of viral antigens. Unlike the other two production technologies, recombinant technology does not use CVVs, but rather produces vaccines synthetically. First, scientists obtain DNA that codes for a viral antigen called hemagglutinin (HA). Then, the DNA is combined with a baculovirus, a virus that infects invertebrates, which creates a recombinant virus. This virus transports the DNA that instructs how to make HA to a host cell. Once the virus enters the U.S. Food and Drug Administration-qualified host cell line, the cells begin to rapidly produce HA. The HA is then purified and packaged as a recombinant flu vaccine.

While there is no significant correlation between a vaccine’s production methods and its effectiveness, the effectiveness does depend on other factors. One of them is age, as evident during the 2019-2020 flu season. While the flu vaccine was 55 percent effective for children of ages six months to 17 years, it had a significantly lower effectiveness of 5 percent for adults ages 18 to 49. Another factor is the similarity between the flu virus the vaccine protects against and the virus contracted in the community. However, it is difficult to determine if the similarity of these flu viruses will help foretell how effective the flu vaccine is. During flu seasons when the flu vaccine and circulating viruses are largely dissimilar, there may be very small benefits to taking the vaccine. On the other hand, when the flu vaccine and circulating viruses do match well, there may be more significant benefits from flu vaccination. But the flu vaccine may still have varying benefits even if there is a good match, as there are still many other factors to consider, like attributes of the vaccinated person, the flu viruses being spread, or what type of flu vaccine is used.

These varying benefits spur scientists to develop new vaccines each year. It is their responsibility to take the aforementioned factors into account when performing their research, and how scientists actually understand the extent to which the flu vaccine performs its responsibility is worth looking into. This part of the process—determining how well a flu vaccine works—is challenging, as most data regarding it depends on statistics received after the flu vaccine is administered. When the flu vaccine is well-adapted to the present flu viruses, scientists can then use such data in future vaccines made in order to prevent forthcoming viral strains in the future. For now, researchers attempt to determine how well the vaccines work in a way similar to public health intervention. Estimates of flu vaccine strength vary based on a variety of factors, ranging from the study design, outcomes measured, the studied population, and the time during which the study was carried out. After collecting this data, the CDC uses mathematical modeling to estimate the number of illnesses associated with the flu regarding hospitalizations, cases, and deaths. The modeling provides a great deal of information regarding the potency of such vaccines and currently adds to the public conversation surrounding appropriate vaccine use. While current flu vaccines provide many with the intended prevention, flu vaccines are always in the works, and at the moment, more effective vaccines are needed. In recent times, the government has been attempting to invest funds and publicly recognize these efforts to create more effective vaccines.

In an executive order issued by the White House in mid-September 2019, President Trump explained a plan to modernize and improve influenza vaccines, stating, “We want a safe and healthy future for every American family.” While the actual vaccine is being reformed as well, the administration is looking to extend the vaccine’s availability to as many American households as possible. The importance of being able to rapidly produce influenza vaccines using scalable technologies in the case of a pandemic has been recognized especially when compared to the recent COVID-19 outbreak. Despite the role of safeguarding the health of American citizens, influenza vaccines are currently produced using time-consuming methods. More efficient, non-egg-based production would allow researchers to select the most relevant strains, but this production is far away from being implemented into the public.

These measures taken by the government demonstrate how administering the flu vaccine is crucial to keeping Americans healthy. While the flu vaccine will always be changing and is often unpredictable, scientists have grown accustomed to researching the virus and its respective strains, working to counteract its effects. In recognizing that developing the perfect flu vaccine is an ongoing process that requires upkeeping every year, Americans must realize the importance of receiving the vaccine in order to set up a safeguard they can fall back on in case they’re exposed to the flu. There are many ways to receive the vaccine, from a family physician to school nurses to local pharmacies. While influenza statistics do show that the vaccine does not provide strict results on the positive spectrum, the opportunity should be taken as a preventative measure. Recently, while the COVID-19 outbreak is causing many Americans to be in a panic, it's a relief to know that influenza was in fact a pandemic in the early 1900s, with its vaccines being in worldwide circulation today. A COVID-19 vaccine is currently in the works, but its future remains to be seen.