Viruses, as we all know, are invisibly small things that make us sick. But is that the whole story?
Zoom in close enough and you'll discover the complex, unseen world of viruses. Some do make us sick, but many others simply exist alongside us as part of the natural world. Most are very beautiful and many, it turns out, look a bit like snowflakes.
It's the time of year for seasonal decorations. So the MRC-University of Glasgow Centre for Virus Research has created a set of papercraft virus snowflakes you can print and cut out. They're a fun way to explore the viruses around us this winter - and the vaccines that protect us from them.
Here are some of our favourites.
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On the first day of Christmas a virus gave to me: a world that is too small to see
An elegantly decorated adenovirus, just 100 nanometres across - that's a ten-thousandth of a millimetre, or smaller than a quarter of the wavelength of visible light.
On the second day of Christmas a virus gave to me: two twinned capsids
Many viruses use repeating protein blocks to package their genetic material (genome) into regular, rounded "capsids". The geminiviruses of plants pull off a beautiful geometrical trick, stacking their proteins into a doubled capsid structure.
On the third day of Christmas a virus gave to me: three genome segments
Most viruses store their genes in one molecule, but some split them into segments - just like how our DNA is divided into multiple chromosomes. This virus, Heartland virus, has three of them.
On the fourth day of Christmas a virus gave to me: four COVID vaccines
There are four main types of COVID vaccine (clockwise from top left): protein subunit vaccines (which use harmless virus fragments), inactivated virus vaccines (using killed virus particles), mRNA vaccines (delivered in tiny lipid bubbles), and adenoviral vector vaccines (using a harmless virus as a delivery vehicle).
On the fifth day of Christmas a virus gave to me: FIIIIVE TIIINY RIIIIIIINGS
Anelloviruses (named after the Latin word for "ring" because of their circular genomes) are extremely common blood-borne viruses. Despite infecting almost everyone on the planet, they don't appear to cause any disease - so they went completely unnoticed for decades.
On the sixth day of Christmas a virus gave to me: six wasps a-laying
Bracoviriforms have formed a remarkable partnership with a particular type of wasp. The wasp passes the virus's genes directly to its offspring, and in return, the virus provides capsids (protein shells) for the wasp to use. The wasp then uses those capsids to disable a caterpillar's immune system, allowing it to lay eggs inside the living caterpillar. Not the nicest story, but that's nature for you.
On the seventh day of Christmas a virus gave to me: seven dogs a-barking
A vaccine made from inactivated rabies virus particles. Rabies vaccines were among the first ever developed, and, unusually, they can protect someone even after a dog bite has exposed them to this otherwise deadly virus.
On the eighth day of Christmas a virus gave to me: eight tools for teaching
Bacteriophage lambda infects the most commonly studied strain of lab bacteria, E coli. Instead of being a nuisance, it turned out to be a revelation. By manipulating its host with a clever set of genetic switches, lambda helped scientists understand how cells and genes are controlled.
On the ninth day of Christmas a virus gave to me: nine childhood vaccines
From January 1 2026, all children in the UK will be offered free vaccines against these nine viruses. They are (clockwise from top left) measles virus (the cause of measles and of measles encephalitis), varicella zoster virus (chickenpox, shingles, and a potential contributor to dementia), poliovirus (poliomyelitis and paralysis), mumps virus (mumps), hepatitis B virus (hepatitis, cirrhosis and liver cancer), human papillomavirus (cervical cancer), influenza virus (influenza), rotavirus (gastroenteritis) and rubella virus (German measles, miscarriage, congenital rubella syndrome).
On the tenth day of Christmas a virus gave to me: ten lunar landers
Bacteriophage T4 is one of the most complex and beautiful of the bacterial viruses. It lands on a bacterium like a tiny lunar module, then squats down to inject its genome and take over the cell. One small step.
On the eleventh day of Christmas a virus gave to me: eleven Christmas dinners
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A wreath of ten crAssviruses - hugely abundant viruses that infect gut bacteria and are part of your normal, healthy microflora. They surround one norovirus, which causes winter vomiting disease, and is not part of your normal, healthy microflora.
On the twelfth day of Christmas a virus gave to me: twelve fights worth winning
Viruses representing pandemics or major outbreaks since the start of the 20th century: four influenza viruses (from the pandemics of 1918, 1957, 1968 and 2009), SARS-CoV-1, SARS-CoV-2, Zika virus, mpox virus, HIV, polio virus and Ebola virus.
The responses to all of these outbreaks were complex and flawed, but in every case their effects would have been far worse were it not for the tireless work of healthcare professionals, scientists and public health specialists. This work must continue - with a space for "disease X", the ghost of viruses yet to come.
If you'd like to see more, you can download and try out the virus snowflakes for yourself, along with lesson plans and other free resources.
Ed Hutchinson, Professor, MRC-University of Glasgow Centre for Virus Research, University of Glasgow
