Flu vaccines have prevented millions of deaths – our research proves it

The 1918 Spanish flu pandemic was caused by a particularly virulent strain of influenza virus. It infected 500 million people, caused around 50 million deaths, and its impact was so severe that global life expectancy fell dramatically. It claimed more lives than the First World War.

In their efforts to develop a vaccine, researchers at the time worked under the mistaken assumption that influenza was caused by bacteria, based on Richard Pfeiffer’s 1892 discovery of the “bacillus influenzae”, which today is known as the bacterium Haemophilus influenzae.

It was not until 1931 that Richard Shope discovered the Influenza A virus in pigs. In 1933, Wilson Smith, Christopher Andrewes and Patrick Laidlaw then discovered the same virus in humans.

Subsequent work has described different versions of the virus surface proteins haemagglutinin (HA) and neuraminidase (NA). Different combinations of these give rise to the influenza A virus subtypes, including the H1N1, H2N2 and H3N2 subtypes that have afflicted humankind for over 100 years.

The first inactivated influenza vaccine for use in humans was developed by Thomas Francis (who also developed the Influenza B virus in 1940) and his student Jonas Salk, who later developed the polio vaccine.

The influenza vaccine was tested for safety and efficacy in the US military during World War II before being licensed for wider use in 1945. However, researchers soon realised that the virus regularly mutated, meaning vaccines needed annual updates to remain effective.

Constant evolution

Various technologies and methods are used in producing flu vaccines. In the northern hemisphere, design for the autumn vaccine begins in February, and is based on the strains circulating at that time.

Over recent decades, vaccines have evolved in response to changes in circulating viruses. In 1948, the World Health Organization (WHO) established the Global Influenza Programme and, in 1952, the Global Influenza Surveillance and Response System (GISRS) to track emerging strains.

These initiatives enabled the production of seasonally updated vaccines, and form the basis for the WHO’s annual recommendation of specific strains to be included in each hemisphere’s immunisations against Influenza A H1N1 and H3N2, as well as Influenza B viruses.

Flu returns annually as an epidemic. It is a constant threat to public health, affecting millions of people and causing severe complications in the most vulnerable: young children, older adults, and people with pre-existing conditions.

How effective are vaccines?

In 2010, the recommendation for full vaccination of the population (from 6 months onwards) marked a major advance in reducing the risk and complications of infection. It also meant that hospitals were under less strain in the winter months. Since then, flu’s impact has diminished greatly, but what do we really know about how effective vaccines are?

To find out, our team conducted a study. We analysed different parameters to estimate the effectiveness of influenza vaccination in preventing and reducing the severity and mortality of infection, especially in the most vulnerable segments of the population.

Our work is a meta-analysis of 119 articles published over the last 10 years, covering a total of 192,705 patients. Our mathematical analysis was validated using data from the TrinetX database, which includes over 6.5 million patients.

We analysed the percentage of the most common influenza viruses such as Influenza A (H1N1 and H3N2) and Influenza B in different age groups: children under 5, people between 5 and 65, and people over 65. In addition, we studied the effectiveness of vaccines against these viruses in the same age groups.

Our results show that vaccines are effective in preventing infection with the different influenza viruses they are intended to prevent. In the case of H3N2, this protection is more limited.

In terms of its effectiveness in preventing deaths, our analysis of the data shows that influenza vaccination is able to reduce infection-associated mortality by half overall, including H3N2 infections.

For at-risk groups – those with pre-existing conditions that make them two to ten times more likely to die after influenza infection – vaccination in some cases reduced their mortality to levels comparable to those of uninfected people. This highlights the vaccine’s ability to protect even those who face the greatest risks.

It’s a fact: vaccines save lives

In a society where vaccine scepticism is on the rise, it is crucial that we gather and analyse all available evidence, share it, and use it to make objective decisions that outweigh opinions or value judgements.

It is true that vaccination does not guarantee that nobody will get infected. However, it does reduce the burden of disease on healthcare systems and, more importantly, it saves lives. Mild or moderate symptoms after infection are a small price to pay when you consider that vaccines protect us from hospitalisation, serious complications and death.

We often hear people say things like “I got vaccinated this year and still got the flu”. However, with the data in front of us, we can be certain that without vaccination, this illness could have been much, much worse.