HEAVY smokers are more than six times as likely to die from a Covid infection compared to people who have never smoked, according to a major new study which challenges claims that cigarettes might offer a protective effect against the disease. 

Researchers said there was a "need for greater clarity" about the relationship between smoking and severe Covid due to "conflicting evidence" which has even led to a clinical trial being established to investigate whether nicotine replacement patches can used as a prophylactic against the infection. 

The study, published today in the BMJ journal Thorax, is the first to pool both observational and genetic data on Covid and smoking. 

Scientists from Oxford University drew on primary care records and information about genetics and lifestyle stored on more than 421,000 people as part of the UK Biobank project. 

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From this cohort, they were able to identify that 1,649 individuals had tested positive for Covid between January and August 2020, of whom 968 required hospital treatment and 444 died as a result of their infection. 

The comparatively high ratio of hospitalisations and deaths to infections during this period reflects the way in which community testing was limited during the initial phase of the pandemic, with most PCR resources targeted to healthcare settings or care homes. 

The researchers cross-referenced Covid outcomes against self-reported smoking status.

They found that 849 of the 1,649 infections had occurred in people who had never smoked, of whom 440 required hospital admission and 159 died. 

The Herald:

Among the 57 who were current - as opposed to former smokers - there were 51 hospitalisations and around 40 deaths. 

Once adjusting for variables including age, sex, ethnicity, deprivation and underlying health conditions, the researchers found that "heavy smoking" - 20 or more cigarettes per day - was associated with a six-fold increase in the risk of death from Covid compared to people who had never smoked. 

Current smokers were also 80% more likely to be admitted to hospital.

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The researchers also found that a genetic predisposition to smoking was associated with a 45% higher risk of infection.

The findings follow a raft of "conflicting evidence" including one study conducted early in the pandemic which reported a lower prevalence of active smokers among Covid-19 patients relative to the general population, and another which  found that smoking was associated with lower risks of Covid-19 mortality. 

A clinical trial involving over 1,600 participants is currently underway in France comparing the spread and severity of the virus in groups given nicotine replacement patches compared to a placebo.

However, a number of other observational studies have since found links between smoking and an increased risk of infection, worse symptoms, and respiratory failure in lifetime smokers. 

“The idea that tobacco smoking may protect against Covid-19 was always an improbable one,” write Dr Anthony Laverty and Dr Christopher Millet of Imperial College London, in a linked editorial.

“A respiratory pandemic should be the ideal moment to focus collective minds on tobacco control,” they add, highlighting a recent warning from the Royal College of Physicians that the UK will miss its target of cutting smoking prevalence to less than 5% by 2030.

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Lead researcher Dr Ashley Clift said: “Our results strongly suggest that smoking is related to your risk of getting severe Covid, and just as smoking affects your risk of heart disease, different cancers, and all those other conditions we know smoking is linked to, it appears that it’s the same for Covid.

"So now might be as good a time as any to quit cigarettes and quit smoking.”