Viruses 'more likely to lead to infection' in the morning, says report

Viruses are 10 times more likely to cause illness in their victims if the infection is contracted in the morning, and late nights increase the impact even further, according to a study by the University of Cambridge.

Scientists infected mice with influenza and herpes viruses and found those infected in the morning had 10 times the viral levels of those infected in the evening.

It is believed the findings could help governments decide the best course of action when pandemics break out, and to determine the correct advice to give to citizens.

Further tests revealed the impact of a disrupted body clock, caused by lifestyle changes such as later nights and jet lag, which created a ‘locked in’ condition that allowed viruses to multiply rapidly.

The study was published in the scientific journal Proceeding of the National Academy of Sciences and thoroughly examined the “circadian regulation of systemic immunity” completed by the human body.

Professor Akhilesh Reddy was one of the lead researchers on the project and said the findings could help people gain a better understanding of the impact of viruses on the body at different times of day

“The virus needs all the apparatus available at the right time, otherwise it might not ever get off the ground, but a tiny infection in the morning might perpetuate faster and take over the body,” he told BBC News.

“In a pandemic, staying in during the daytime could be quite important and save people's lives, it could have a big impact if trials bear it out.

“The time of day of infection can have a major influence on how susceptible we are to the disease, or at least on the viral replication, meaning that infection at the wrong time of day could cause a much more severe acute infection.”

A particular gene called Bmal1 was a major focus of the study, as relatively low levels of it in the morning makes the body more susceptible to infection.

Professor Reddy’s colleague Dr Rachel Edgar said the findings show regular shift workers could be “prime candidates” for receiving annual flu vaccines, given their disrupted body cycles.

“[The study] indicates that shift workers, who work some nights and rest some nights and so have a disrupted body clock, will be more susceptible to viral diseases,” she said.

The researchers additionally found Bmal1 levels undergo major seasonal variations, explaining why people are more vulnerable to viruses such as influenza during the winter, when the gene was found to be less active.

Meanwhile, bacteria and parasitic organisms are thought to be relatively unaffected by the cycle of the day as they are not dependent on overwhelming cells in order to replicate.