Pfizer's Covid vaccine may not work as well if you're fat

Pfizer's Covid vaccine may not work as well if you're fat

March 1, 2021

Pfizer’s Covid vaccine may not work as well if you’re fat: Obese people make HALF as many antibodies after getting two doses, study claims

  • Italian study said jabs are 50 per cent less effective in those who are obese
  • But experts said that was ‘suspiciously high’ and may be linked to small sample
  • Other research has suggested the flu vaccine is half as effective in obese people 

Pfizer’s coronavirus vaccine may be less effective in obese people, scientists have warned.

Severely overweight healthcare workers generated only half the antibodies to fend off Covid after receiving two doses of the jab, compared to healthy people.

Italian researchers said obese people may need another top-up vaccine, or bigger doses, to protect them against the disease.

The above results show the antibody levels in people of differing weights after getting their second dose. They reveal there was no significant difference between them, suggesting more tests are needed. Separate results indicated the jabs were half as effective in obese people

Scientists said obesity is known to lead to jabs being less effective because it can stop cells functioning normally

Severely overweight people are already considered to be more at risk of becoming critically ill or dying if they get infected.

Scientists say this may be because they are more likely to have other conditions —such as diabetes and high blood pressure — that make them more vulnerable. 

Experts today said it was also well known obesity — defined as having a BMI above 30 — hampers the effectiveness of jabs.

Previous research has suggested the flu vaccine, which is dished out every winter, could be half as effective in severely overweight people.

But the Italian study, yet to be scrutinised by fellow scientists, is believed to be the first time the same link has been found for Covid.

Carrying added weight can lead to the immune system being constantly inflamed, impairing its function, according to experts.

For comparison, in healthy people it only triggers inflammation when it is fighting an infection. 

Almost a third of adults in England and nearly 40 per cent in the US are classed as obese, according to estimates. 

They also studied the antibody responses by age, but found no differences in concentrations (error bars are shown to overlap). This suggests that jabs trigger as effective immune responses in over-70s as among younger age groups

In the study, 248 participants received two doses of the Pfizer vaccine at the Rome-based Istituti Fisioterapici Ospitalieri.

Scientists analysed their blood for levels of antibodies seven days after the second dose was administered.

Antibodies are virus-fighting proteins that can stop a Covid infection. They are a major part of the immune system – but not the only part.

Results showed that while those who were a normal weight had a high concentration (325.8), those who were obese had half this level (167.1), on average.

But the study only included 26 obese people, which is considered to be too small to draw concrete conclusions.

And there was no significant difference in results between those who were obese and normal weight, meaning more tests are needed. 

It also considered vaccine responses by age — but found no significant difference between the different groups. 

Professor Ian Jones, a virologist at the University of Reading, told MailOnline he thought the figures looked ‘suspiciously high’.

‘It’s probably the small numbers (of participants),’ he said. ‘But that an effect is seen is not surprising.

‘It would be nothing to do with the vaccine, all would be similar. It is the individual’s response that is compromised.’

He added it was a ‘general finding’ that jabs are less effective in obese people.

‘It’s not entirely clear why but it may be related to metabolic syndrome which in turn has a knock-on effect to many cell functions, including immunity,’ he said.

Metabolic syndrome is the medical term for a cluster of conditions, including high blood pressure, heart disease and type 2 diabetes.


Studies have shown obese people are more likely to suffer serious complications or die from infections, such as the flu. 

Doctors say the immune systems of fat people are constantly ramped up as they try to protect and repair the damage inflammation causes to cells. 

Using all its energy fending off inflammation means the body’s defence system has few resources left to defend against a new infection like Covid-19. 

Dr Dyan Sellayah, a lecturer in cellular and organismal metabolism, University of Reading, said obese people tend to have dysfunctional immune systems.

‘Their fat tissue for example becomes a reservoir for immune cells known as macrophages. While these cells reside in our fat under normal circumstances, in obesity they are at higher frequency and become more troublesome (they start to secrete inflammatory cytokines) and negatively impact on immune and metabolic health.’ 

Obese people might eat a diet with very little fiber and antioxidants – which keep the immune system healthy – such as fruit and vegetables.  

Most patients with a BMI of over 40 suffer from breathing problems that range from simple shortness of breath to a potentially life-threatening condition known as obesity hypoventilation syndrome (OHS).

Public Health England (PHE) has previously suggested that obesity leads to fatty tissue around the upper airway, and a heavy chest can directly reduce lung function. 

Excess weight may make it more difficult for the diaphragm and lungs to expand and inhale oxygen. Starved of oxygen, organs will begin to fail.  

But other experts have disagreed with this theory, saying severely ill Covid-19 patients end up on ventilators anyway and still end up with worse outcomes. 

There are several other factors that may increase an obese person’s chance of falling seriously ill with coronavirus, including a lack of exercise.

Studies have shown that physical activity increases the numbers of certain immune cells that help to bolster immune activity.  

Clogged up arteries also make it hard for blood carrying immune cells to pass through and repair cells around the body.  

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