What happens when we catch a cold?
Most common colds are caused by the human rhinovirus, with other respiratory viruses-including respiratory syncytial virus, human metapneumovirus, and parainfluenza viruses- playing a lesser role. There are few, if any, specific features of a cold that tell us which virus is responsible for the cold.

The virus first infects the cells lining of the nasal passages, known as epithelial cells which respond to infection by initiating an anti-viral defence. The cells make anti-viral defence proteins, known as interferons, and others called cytokines that gather inflammatory cells, make mucus and cause swelling of the lining of the nose. Parents can certainly recognize the effects of this in the child, with a stuffy and runny nose and sneezing being common in children with colds. A dry cough can also be part of a simple cold.

A successful anti-viral defence response would see the cold limited to the nose with the symptoms disappearing over a few days as the virus is cleared from the cells. This is what happens with most colds but sometimes the virus spreads to the lungs causing more severe or congested coughs that last more than a few days.

Are colds in children with asthma different?
While not everyone agrees, it appears that young children with asthma, or who are at risk of developing asthma, may catch more colds than children without asthma. The reasons for this are not clear but it may be that children with asthma have a less effective anti-viral defence that allows the children to catch colds more easily and allows more colds to spread from the nose to the lungs. There is some evidence that asthmatics make less interferons in response to viral infections but more research is needed to prove this and to know what to do about it if it is true.

Do colds cause asthma?
Colds by themselves are not likely to cause asthma. We do know that asthma runs in families and that children who have asthma in their family are more likely to develop asthma themselves. We also know the risk is increased for children who develop allergies in early life to common factors in the environment, such as house dust mites, cockroaches, cats, grasses and other pollens and to foods. Children that wheeze when they catch a cold, especially in the first 2-3 years of life, are at increased risk of developing asthma. So, frequent colds occurring in children with a family history of asthma and who have allergies in early life increase the risk of asthma.

Do colds make asthma worse?
Colds are the most common reason children with asthma have asthma attacks. This is true both of mild attacks and those severe enough for children to need hospitalization. This does not mean that all colds in children with asthma will cause asthma attacks, but most attacks come with colds. The virus causing a cold can leave an asthmatic child’s airways more twitchy for several weeks after the cold has passed, increasing the risk that the next cold will result in worsening asthma. The best way to guard against this is to make sure that your child does not miss her medication following a cold. Children who have frequent colds with asthma symptoms are likely to need “preventer” medications and should be taken to the doctor to see whether this is the case.

How can I prevent my child from catching cold?
The risk of catching a cold is increased by being exposed to other people, especially children, who have a cold. When someone has a cold, he is most infectious for the first few days of the cold; at the time he has the most “cold” symptoms. There are three basic ways that respiratory viruses spread from person to person:
1) Breathing in virus in small particles generated by coughing
2) Expelling large particle droplets from saliva while sneezing
3) Picking up virus on the hands from an infected person or from a contaminated surface and transferring the virus to yourself by touching your eyes or nose.

More virus colds are caught from contaminated hands than from directly breathing in particles generated by coughing or sneezing. This is why hand washing is so important in limiting the spread of colds from one person to another.

General measures to boost immunity against colds include: keeping fit by moderate exercise; eating a good balanced diet with fresh fruit and vegetables; and getting enough sleep. There is no evidence that taking extra vitamins, including vitamin C, or natural products, such as ginseng or echinacea prevent colds, and clinical trials with these products have not shown any benefit. Cigarette smoking, living with smokers or being exposed to increased levels of air pollution increase the risk of children catching colds.

Specific measures to boost immunity against colds include: immune stimulants such as probiotics, prebiotics and bacterial lysate products, such as OM85 (Bronchovaxom-not available in the United States); interferons; Vitamin D; and anti-inflammatory antibiotics (e.g., macrolides). There have been a number of clinical trials in children that have recurrent colds, recurrent wheeze or asthma using these types of products. Some trials using probiotics and similar products have shown a reduction in the number of colds children have, but not all trials are positive. One major limitation in the probiotic trials is that there is no way to test just how “probiotic” a particular product is and this may vary from batch to batch or from product to product.

Trials of Bronchovaxom generally show a benefit, with a reduction in colds or wheezing episodes by about one-third. In one study, the children took Bronchovaxom during winter only but had a reduction in wheezing episodes that lasted for the 12 months of the trial. Bronchovaxom does not contain any live organisms, showing that live organisms are not necessary for a product to have a beneficial effect. It is not known just how these products may help prevent children catching colds but the best theory is that this occurs by generating immune regulating cells in the gut that go to the airways to provide immune support. It is well known that immune cells do circulate between different parts of the body, so this theory is plausible.

Interferons are part of the body’s natural anti-viral defence system so if this is deficient, using this as a treatment seems logical. There is no proof, however, that giving interferons after a cold has begun and the symptoms are recognized would actually prevent the cold getting worse or shorten its duration. Clinical trials in adults are currently underway, so we will need to wait and see whether these are effective before this therapy could be used in children.

People who are deficient in Vitamin D seem to be at a higher risk of wheeze and asthma and there is some evidence that correcting this deficiency may reduce the risk of colds and asthma attacks. While it might be tempting to extrapolate from this to giving children vitamin D supplements to prevent colds and asthma, there is no evidence that having vitamin D levels above the recommended levels has any benefits at all.

Macrolide antibiotics have anti-inflammatory properties and there is evidence from cell studies in the laboratory that they can boost anti-viral immunity. However, there is no direct evidence that they can prevent colds in children. Indiscriminate use of antibiotics can lead to the development and spread of bacteria that are resistant to antibiotics. This poses a much greater danger to the community that far outweighs any theoretical benefit of anti-inflammatory antibiotics preventing colds.

There are no safe and effective vaccines currently available against the most common respiratory viruses that cause colds, with the exception of the influenza vaccine.

The table summarizes the measures that are likely to be beneficial in preventing children with asthma catching colds and those that are not.

Effectiveness Interventions
Most likely to be beneficial Hand hygiene
Breastfeeding (in the first 6 months of life)
Likely to be beneficial Healthy lifestyle with regular exercise, balanced diet, avoidance of tobacco smoke exposure, plenty of sleep and low stress.
Reduced exposure to air pollution and tobacco smoke
Vitamin D (if deficient), garlic, inteferons
Unknown effectiveness Vitamin C, macrolide antibiotics, echinacea, ginseng
Likely to be ineffective or harmful Antibiotics, vitamin D (if levels already sufficient)

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From issue: 29/01-02