Obesity reduces vaccine effectiveness

Facts

• Globally, over 39% of adults are overweight and 13% have an obesity problem
• Over 30% of adults are obese in Australia and USA
• Obesity is associated with:
  • Reduced ability to fight against diseases and infections
  • Increased rate of infection
  • Reduced recovery from bacterial and viral infections
  • Reduced response to vaccines
• Vaccines specifically enhanced to overcome the reduced immune responsiveness in these vulnerable populations should be considered

History of flu

Every year, influenza “the flu” results in ~1 billion infections, 3–5 million cases of severe illness resulting in hospitalisation and 300,000–500,000 deaths.

The severity and global effect (health threat) of influenza depends on multiple factors, including the virulence (strength of virus strain) and the level of pre-existing immunity.

Influenza vaccines are formulated every year to capture the known existing and past strains, as the influenza virus rapidly changes and evolves over time.

Slightly different versions of a virus are called “new strains”. During the 2009 pandemic with influenza A H1N1, morbid obesity with body mass index (BMI) >35–40 kg per m² was recognized as an important risk factor.

A normal healthy BMI is between 18.5 and 24.9 kg/m².

Obesity links to flu susceptibility

Not only is obesity a risk factor for flu complications, but it makes vaccines less effective.

Why?

Obesity is characterised by a state of chronic inflammation, meaning there is an imbalance between the good and bad factors that circulate around your body.

These factors can include hormones that negatively impact your immune system turning it into overdrive. This can make you more susceptible to infection, reduced ability to fight infections and a slower recovery time.

In fact, viral replication – the process through which viruses are formed – is ramped up in excess if you have obesity.

Not only will this make you sicker, but also more likely to spread the disease – contributing to a flu outbreak or “pandemic”.

Increased severity of secondary bacterial infections are also more likely.

Researchers have found that vaccinated obese adults are twice as likely to develop influenza and influenza-like illness compared to healthy weight adults  (BMI<25 kg/m²).

These findings question the effectiveness of vaccines in individuals with excess body weight (BMI>30 kg/m2).

Science behind immunity

The primary function of the immune system is to defend the body from pathogens (bacteria or viruses that can cause disease).

The body’s systems (tissues, cells, and proteins) involved in the immune system response work together to achieve this function.

B cells are one example of an important cell type that are an essential component of the immune system. B cells make antibodies (proteins) that attach to the surface of a pathogen and prevents entry into healthy cells helping to fight infection.

T cells are another example of an important cell type that are an essential component of the immune response.

T cells kill viruses by attacking and killing cells that have been infected by the virus.

T cells from influenza vaccinated obese adults are less switched on when triggered by vaccines of influenza strains.

This explains why vaccine efficiency is reduced in obesity.

Immune System

The immune system is comprised of two components the innate or immediate and adaptive or delayed immune response.

It takes time for T and B cells to respond to new antigens (part of the pathogen that is detected by the body) when a virus causes an infection.

Once exposed to the pathogen, these cells develop a “memory” for the virus so that they are ready for the next infection.

As part of the adaptive immune response, some T and B cells change into memory cells.

Memory cells “remember” antigens.

If a person becomes infected with the same pathogen again, these cells can quickly begin fighting the infection.

When a virus strain changes, it means the body needs to respond to this new strain with different “antigen/s” by triggering a new immune response.

Vaccines assist with providing protection.

They expose the body to a low dose or part of the virus so memory cells can be made for a quicker immune response when infection with the real virus occurs.

It may take up to 14 days for your body to build up immunity after influenza vaccine. The first immune response is called the “primary response” and the second response is called the “secondary response”.

But what about the elderly, don’t they have reduced immune response also?

The increased susceptibility of the elderly to infection presents a major challenge to public health services.

An aging immune system causes increased infection rates in elderly people.

Vaccination protects the elderly against diseases such as influenza and is highly recommended.

However, reduced function of immune system with age affects the response to immunisation.

Elderly have reduced efficacy to immunisation of 17–53% in the elderly compared with 70–90% in healthy adults.

So, what does this all mean for vaccine development and COVID-19?

In addition to susceptibility to influenza, recent evidence suggests young people with obesity are more likely to be infected with COVID-19.

Once infected, those with obesity are more likely to require respirators in hospital.

Obesity is associated with increased risk for cardiovascular disease, hypertension and diabetes, conditions that also compromise the immune system and increase risk for COVID-19 complications.

Take-home message

Obesity reduces vaccine effectiveness.

Keeping fit through regular physical activity (20-40 min/day) and maintaining a healthy body weight (BMI 18.5-24.9 kg/m²) will substantially reduce your risk of infection by improving your immune responsiveness.

For more information on vaccine immunology.

Author

Dr Hayley M O’Neill, PhD

Hayley is the Business Development Manager at Clueo Clinical Pty Ltd. She  has over 12 years combined experience in clinical and pre-clinical research and development, and management. She was an NHMRC postdoctoral research fellow. Her expertise is metabolic diseases and weight loss. She is passionate about health and strives to improve our current knowledge to enable development of new strategies, improve patient outcomes and lower disease burden on society.

LinkedIn

Other articles by this author:

• Are stress and isolation sabotaging your weight loss efforts?
• The power of a healthy gut