Four out of ten Brits may naturally show fewer flu symptoms

Thinking of throwing a sicky? Your usual alibi might be a little less convincing after today’s report by The Independent that "Four in 10 Britons immune to flu symptoms, leading to hopes of a new vaccine".

A survey of 1,414 people found that 43% of them had a type of immune cell – T cells – that partially protects against the symptoms of a flu infection.

Researchers found that T cells target specific parts of the flu virus machinery, called nucleoprotein. So the lucky 43% had less flu symptoms after becoming infected.

The logic is that if people have fewer symptoms, they are less likely to spread the virus through coughs and sneezes, and this may slow the spread of both seasonal and pandemic flu strains, such as swine flu. The logic is plausible, but was not directly tested in this study.

The research team suggested vaccines that boost T cell numbers might be worth exploring as an alternative to those that try to stop flu virus infection altogether.

An added potential benefit of their finding was that protection from symptoms of one virus strain showed similar signs in another. That said, only two virus types were tested, so we don’t know whether this "cross-reactivity" is widespread.

We know coughs and sneezes spread diseases, but do you know what to do about it? Read how to prevent flu. 

Where did the story come from?

The study was led by researchers from University College London and was funded by a large range of charity, government and university sources, including the Medical Research Council, the British Heart Foundation and Cancer Research UK. 

The study was published in the peer-reviewed American Journal of Respiratory and Critical Care Medicine.

Generally, the UK media reported the story accurately. Hope of a new vaccine was widely discussed by the media. This was not investigated in the study, so remains speculative at this stage.

What kind of research was this?

This was a cohort study looking to understand naturally existing resistance to the symptoms of flu in the hope the knowledge might one day be useful in lessening the spread of seasonal and pandemic flu.

The study authors say that a high proportion of flu (influenza) infections do not cause flu symptoms like coughing and sneezing – which is the main way the virus spreads from person to person.

Animal, human and observational studies suggest T cells, part of the immune system, are involved in lessening flu symptoms in some people, but the impact of this at a population level is not known.

The T cells are thought to target an important part of the flu virus machinery called nucleoprotein. Nucleoprotein exists across many strains of flu virus, so T cell-linked immunity against this key part of the virus may help to confer protection from symptoms for a wide range of different strains. If true, the hope is this might be harnessed to form a more effective vaccine and limit the spread of both seasonal and pandemic flu through coughs and sneezes.

What did the research involve?

The researchers measured flu-specific T-cells in an English population cohort during seasonal and pandemic periods between 2006 and 2010.

A total of 1,414 unvaccinated individuals had T cell measurements. They were part of a "Flu Watch Study". The study recruited successive groups each year via random selection of households from general practice registers across England.

Blood samples were taken prior to the natural circulation of flu virus to measure baseline antibody and T cell responses. Participants were then followed up intensively over the flu season to determine who got ill with flu. This involved weekly follow-up from late autumn to late spring, using automated telephone calls or emails.

Nasal swabs were also taken and analysed in the laboratory to confirm flu infection.

What were the basic results?

The study found people with T cells targeting flu virus nucleoprotein before exposure to the virus generally had less symptomatic disease (odds ratio, 0.27; 95% confidence interval, 0.11 to 0.68) during pandemic and seasonal periods.

They found T cells reacting to a specific flu virus (H3N2) also reacted to a different one (H1N1).

Influenza-specific T cell responses were detected in 43% of people, indicating a lot of people carried some level of immunity that showed lesser symptoms.

This link was independent of baseline antibodies. The antibodies actually help prevent flu infection, whereas the T cells are involved in lessening symptoms. So this confirmed people were still getting infected, but symptoms were varying in line with T cell characteristics.

How did the researchers interpret the results?

"Naturally occurring cross-protective T cell immunity protects against symptomatic PCR-confirmed disease in those with evidence of infection and helps to explain why many infections do not cause symptoms. Vaccines stimulating T cells may provide important cross-protective immunity."

Conclusion

A study of 1,414 unvaccinated people showed those with T cells targeting virus nucleoprotein still got infected by flu, but had fewer symptoms. The logic is that people with fewer symptoms are less likely to spread the virus through coughs and sneezes, which may slow the spread of both seasonal and pandemic flu strains.

This is plausible, but was not directly tested in this study, so we don't know if it's true in real life. The research team suggested vaccines that boost T cell numbers might be worth exploring, as an alternative to those that try to stop virus infection altogether. An added potential benefit of their finding was that lessened symptoms in one virus strain showed similar signs in another.

That said, only two virus types were tested, so we don't know whether this "cross-reactivity" is more widespread.

The findings suggest around 43% of people had some form of this natural immunity, but it's not clear if this is across a broad range of flu viruses or just a couple.

The study is encouraging, but is in its early stages of understanding, raising as many questions as it answers. For example:

• Is it possible to boost this natural symptom immunity in those that have it?
• How common is this natural immunity in the public?
• Is it possible to transfer this symptom immunity to those that don’t have it?
• How useful is this at preventing new cases of flu or deaths from flu?

If you are particularly vulnerable to the effects of a flu infection due to factors such as having a chronic disease or being aged 65 or over, then you should take advantage of the seasonal flu vaccine. Read more about who should get the “flu jab”.