The "common" cold is aptly named...it is something nearly everyone encounters. The U.S. population experiences nearly a billion colds annually. Children usually have about six to ten colds per year...adolescents and adults have about two to four. Adults over 60 typically have less than one cold per year.^10762,10763

Influenza ("the flu") is much more serious...and much less common than the common cold. Each year 35-50 million people in the U.S. get the flu. Most people recover. But the flu still causes complications, which lead to 100,000 hospitalizations and more than 50,000 deaths each year.¹⁰⁷⁶⁴
 

More than 200 different viruses can cause the common cold. The rhinovirus is the most common. It's responsible for 30% to 50% of all colds. It is spread both by contact and through airborne transmission. Rhinovirus infections can occur throughout the year but peak between April and May, and again in September.¹⁰⁷⁶⁵ In autumn, rhinoviruses cause 80% of all upper respiratory infections.¹⁰⁷⁶⁶

The flu is caused by 3 types of viruses...influenza A, influenza B, and influenza C. The influenza A virus is responsible for pandemics...flu outbreaks that spread worldwide. Influenza A causes severe disease and a significant number of deaths, even in young people. The influenza B virus doesn't cause pandemics, but can cause severe disease in the elderly and other high-risk patients. Influenza C causes mild disease with no seasonal variation.¹⁰⁷⁶⁷

Flu season typically lasts from November to March. Different vaccines are needed every year because of changes in viral proteins, especially in influenza A. Two proteins on the surface of the virus facilitate viral spread in the respiratory tract. These proteins can change. The changes produce what looks like a new virus to the immune system. Each time this happens the population doesn't have immunity to the "new" virus. This means the influenza virus reinvents itself to some degree every year or every few years. The greater the changes, the greater the risk for a pandemic.¹⁰⁷⁶⁷

Each year's flu vaccine is an educated guess by the U.S. Public Health Advisory Committee on Immunization Practices. This group predicts which viruses are likely to cause disease in the upcoming flu season. This decision is made 6-9 months in advance to allow production time for vaccines. A faulty prediction can result in a vaccine which doesn't protect against the season's prevalent influenza strains.¹⁰⁷⁶⁷

Cold and flu viruses are usually transmitted by hand contact with secretions that contain the virus...either directly from an infected person or indirectly from environmental surfaces such as telephones and doorknobs. Subsequent rubbing of the eye or nose can lead to infection.^10763,10766

Viral transmission can also occur by inhalation. Aerosols from an infected person enter the respiratory tract of a new host and begin colonization. Small-particle aerosols, which are thought to be the means of influenza and adenovirus transmission, can linger in the air for an extended period of time.^10763,10766

There are a lot of myths about causes of the cold and flu. For example, some people believe becoming chilled or wet can cause a cold or flu. But this isn't true.¹⁰⁷⁶⁶ It may be the common timing of cool weather and peak flu season. Cold weather tends to keep people inside where exposure to infected individuals can occur more easily.

Some people think smokers have more colds. Actually, cigarette smoking doesn't affect the incidence of colds and flu. But smokers do have more severe symptoms and longer duration of symptoms than nonsmokers.^10763,10769

Viruses colonize respiratory cells, triggering the release of histamine, leukotrienes, interleukins, tumor necrosis factor, and other cytokines. The flu viruses cause extensive damage to the respiratory epithelium. In contrast, cold-causing rhinoviruses themselves don't cause changes to respiratory tissue. Rhinovirus symptoms may be caused by the body's own inflammatory response to the virus.^10763,10766

Colds typically begin with sore or scratchy throat, sneezing, nasal discharge and stuffiness.^10763,10766 Otitis and sinusitis can sometimes follow a cold. The flu often begins with a sudden headache, fever, myalgia, and malaise.¹⁰⁷⁶⁷ Influenza complications include viral and secondary bacterial pneumonia.^10763,10766

*Note: Many natural products are tried for colds and flu, but very few have reliable evidence that they work. Inclusion in this list does NOT imply that these products are effective for colds or flu.
 

Vaccines

The development of a vaccine against cold-causing rhinoviruses is unlikely. There are many different types of rhinovirus. These different types don't share enough in common to create an effective vaccine.

Several vaccines against other cold-causing viruses, Respiratory syncytial virus (RSV) and parainfluenza virus are in early clinical trials.¹⁰⁷⁶⁶ There are options already available for high-risk neonates and children up to age two...the RSV vaccine (palivizumab, Synagis) and the RSV immune globulin (RespiGam).

There are many more options available for preventing the flu. Flu vaccines are very effective. They can prevent severe disease, hospitalization, and death. In fact, the U.S. Centers for Disease Control and Prevention encourages vaccination for EVERYONE over 6 months of age, except for those with contraindications.

Most people should get flu immunizations in October and November. Patients are usually protected within 2 weeks of the shot and it lasts for about 6 months. Flu vaccines (FluShield, Fluzone, Fluvirin) are trivalent...each includes two influenza A strains and one influenza B strain.¹⁰⁷⁷³

Children age 9 and under who are receiving a flu shot for the first time should receive 2 shots spaced a month apart.¹⁰⁷⁶⁷ More than one flu vaccine per year in adults provides no additional benefit.^10861,10862

FluMist is a new intra-NASAL vaccine. FluMist contains live attenuated flu viruses. Traditional influenza vaccines contain inactivated influenza viruses. FluMist is NOT recommended for people under age 5 or over age 49, pregnant women, or patients with chronic disease.

Since FluMist is a live-virus vaccine, it can't be given to immunocompromised patients or their caregivers. This is because someone receiving a live-virus vaccine might transmit virus to an immunocompromised patient. The flu SHOT may be preferred for family members, healthcare workers, and other close contacts of immunocompromised patients.¹⁰⁷⁷⁴

Antivirals

Antiviral drugs can be used as alternatives to flu immunization for patients who can't get a flu vaccine. Though they must be used throughout flu season to prevent the flu. Amantadine (Symmetrel) and rimantadine (Flumadine) inhibit the growth of influenza A. But they aren't effective against influenza B. Their use is also limited, particularly amantadine, by adverse effects...insomnia...restlessness... anxiety.^10775,10776

Relenza (zanamivir) and Tamiflu (oseltamivir) are a newer class of antivirals...neuraminidase inhibitors. They prevent viruses from penetrating the surfaces of healthy cells and inhibit the release of viruses from infected cells. Zanamivir and oseltamivir seem to be equally effective. The neuraminidase inhibitors may be better tolerated than the older antivirals. Zanamivir and oseltamivir are effective against both influenza A and B.^10775,10776

Zinc is sometimes used to prevent colds. Zinc inhibits rhinovirus replication in vitro, but there's no evidence this happens in vivo. There's no evidence zinc is effective for preventing colds. ^{10780,10783,10784} Tell patients dietary or supplemental zinc won't PREVENT colds.

Immunomodulators

Many people try natural products promoted to "boost or support the immune system." But this approach may not offer much help. Some research suggests that a virus's ability to infect a host may be MORE important than immune system function in catching a cold or flu.¹⁰⁷⁶⁸ In other words, a virus may be able to cause illness even in the presence of a healthy immune system.

Andrographis (Andrographis paniculata), also known as "Indian echinacea," is used to prevent both colds and flu. Andrographis is thought to have immunostimulant properties.²⁷⁶⁶ There's some preliminary evidence that suggests andrographis might reduce the risk of catching a cold. But it can take two months of treatment to see this benefit.²⁷⁷² And it's unclear how long this benefit lasts. It's too soon to recommend it.

Astragalus (Astragalus membranaceus) is a Chinese herb promoted to prevent colds and flu. There's some evidence astragalus can stimulate lymphocyte production.^3713,10777 But there's no clinical evidence it's effective for cold or flu prevention. Don't recommend astragalus.

Echinacea (Echinacea angustifolia, Echinacea pallida, Echinacea purpurea) is widely used to prevent upper respiratory infections including colds and flu. In vitro research suggests that echinacea stimulates the immune system, causing macrophages to produce tumor necrosis factor, interleukin-1, and beta-interferon.^6388,6389 But echinacea does not seem to be effective for preventing colds.^{3281,3282,6386,10782} Don't recommend echinacea for PREVENTING colds and flu.

For the latest on Echinacea, see "Echinacea for the Common Cold," Detail-Document #210911.

Garlic (Allium sativum) is tried for preventing colds. Garlic has immunostimulant activity and might also have antiviral activity. There's some evidence that allicin-containing garlic SUPPLEMENTS reduce the risk of catching a cold.¹⁰⁷⁸⁷ Allicin is the active component in garlic. Patients taking daily supplements between November and February have one fewer cold than patients taking placebo.¹⁰⁷⁸⁷ But there's not enough evidence to recommend garlic for preventing colds.

Garlic has dose-related adverse effects...most commonly bad breath and body odor. Tell patients taking warfarin that garlic can increase their INR.^{616,4802,4803}

Panax ginseng might have immunostimulant effects. Some clinical evidence suggests that Panax ginseng might protect against colds and improve response to the flu vaccine. When Panax ginseng 100 mg per day is started 4 weeks prior to influenza vaccination and continued for 8 weeks thereafter, it seems to reduce the risk of contracting both the cold and flu. The mechanism for this effect is unknown, but Panax ginseng might increase natural killer cell activity and the antibody response to vaccination.⁵⁸⁹ There's not enough evidence to recommend Panax ginseng for this use. Panax ginseng is usually well-tolerated. Insomnia is the most common complaint. The safety of long-term use is unknown. Tell patients to limit Panax ginseng use to 3 months.⁵⁸⁹

The brand Cold-fx is getting lots of attention. For the latest on North American ginseng (Panax quinquefolium), see "North American Ginseng Extract (Cold-fX) for the Common Cold," Detail-Document #211212.

Some research suggests that milk fortified with the GG strain of Lactobacillus rhamnosus can modestly reduce the incidence of respiratory infections in young children in day care.⁸⁵⁶⁵ Lactobacillus GG might stimulate immune function.⁴³⁹⁹ It appears to increase phagocytic activity of leukocytes.^7756,7757 Other research suggests a combination of the essential fatty acids linoleic acid and alpha-linolenic acid can reduce respiratory infections in children. These fatty acids might have a beneficial effect on immune function.¹⁰⁷⁸⁵ But in adults, dietary fatty acids don't seem to affect immune response to bacterial infection.¹⁰⁷⁸⁶ Don't recommend lactobacillus or fatty acids to prevent respiratory infections.

Multivitamin-mineral supplements don't seem to affect the incidence of acute respiratory infections. Supplemental vitamin E doesn't lower the risk of infection. But it might reduce the severity of illness.¹⁰⁷⁸⁸ Supplementation with zinc and selenium might improve antibody response to the flu vaccine in elderly patients with mineral deficiencies.⁶⁵⁵³ But there's no evidence that zinc and selenium supplementation helps healthy patients with adequate dietary intake. Tell patients there's no evidence multivitamins or minerals prevent colds and flu.

Vitamin C has long been promoted for colds and flu...and has generated lots of controversy. Vitamin C might help immune function. It seems to increase T-lymphocyte activity, phagocyte function, leukocyte mobility, and possibly antibody and interferon production.^1963,1965 But most evidence suggests that even in doses up to 1 gram per day, vitamin C does NOT prevent colds.^{1967,6458,9832} Likewise DIETARY vitamin C intake doesn't seem to affect the risk of getting a cold.¹⁰⁷⁸⁰

Suggest to patients interested in using vitamin C to get five servings of fruits and vegetables per day. This provides about 200 mg of vitamin C which is adequate for good nutrition.³⁰⁴²

Antivirals

Treatment of the common cold with antivirals has not been successful so far. On the other hand, treatment of the flu with antiviral drugs is well established. Amantadine and rimantadine are used to treat influenza A, but viral resistance can develop in about 25% to 35% of patients.

The neuraminidase inhibitors...oseltamivir and zanamivir... are effective for both influenza A and B. When treatment with neuraminidase inhibitors is begun within 48 hours of the onset of symptoms, the duration of the flu is cut by one to two days.¹⁰⁷⁶⁶ Neuraminidase inhibitors also decrease the risk of flu complications such as pneumonia and otitis media.^10776,10791 Significant viral resistance has not been reported for these newer antivirals.¹⁰⁷⁷⁵

Antihistamines

Conventional treatment of colds is symptomatic. First-generation antihistamines...chlorpheniramine and clemastine...can decrease sneezing and rhinorrhea, probably because of their anticholinergic activity.^10766,10792 Drowsiness is a prominent side effect, however. Second generation antihistamines (loratadine, fexofenadine, etc) aren't effective for symptomatic relief because they have hardly any anticholinergic activity.

Decongestants, Anticholinergics, and Anti-inflammatories

Oral or intranasal decongestants can dilate nasal passages.¹⁰⁷⁶⁶ Tell patients to limit intranasal decongestant use to three to five days to avoid rebound congestion. Intranasal ipratropium (Atrovent nasal spray) also relieves sneezing and rhinorrhea associated with colds.¹⁰⁷⁹³ NSAIDs have shown effectiveness in reducing cough, possibly by blocking prostaglandin action. NSAIDs are also useful for headache, malaise, sore throat pain, and other systemic complaints.^{10763,11104,11105,11106,11107} But oral or intranasal steroids, with more potent anti-inflammatory activity, are not clinically useful for treating colds.¹⁰⁷⁶⁶Antitussives and mucolytic agents are frequently used, but their efficacy in colds is unproven.¹⁰⁷⁹⁴ Even codeine seems to be no more effective than placebo for treating coughs associated with colds.¹¹¹¹⁰

Immunomodulators

Lots of people take natural medicines to TREAT the common cold and influenza. Unlike conventional treatment, which is primarily directed at symptoms, many natural medicines are used to "strengthen the immune system."

Andrographis seems to significantly improve symptoms of the common cold when started within 72 hours of symptom onset. Some symptoms can improve after two days of treatment, but it typically takes four to five days before maximal symptom relief. Andrographis doesn't seem to help cough. Most studies have used the proprietary product Kan Jang, standardized to contain 4-5.6 mg of the andrographolide per tablet. Tell patients wanting to use andrographis to stick to products standardized to 4-5.6 mg of andrographolide. The safety of more concentrated products is not known.^{2744,2773,2774,5784,10795}

Echinacea is frequently used alone or in combination with other herbs to treat colds and flu. Although it's commonly thought of as an immunostimulant, echinacea might actually have anti-inflammatory effects.^{10797,10798,10799} Theoretically, echinacea might reduce cold symptoms via anti-inflammatory activity similar to NSAIDs.

Most studies show that echinacea can reduce symptom severity and duration from 10% to 30%.^{1412,6384,6386,6392, 8228,10782,10802} The active constituent(s) isn't known, so products used in research are not standardized.¹⁰⁸⁰⁰ Dose can also vary by product. For example, a tablet containing 6.78 mg of Echinacea purpurea crude extract based on 95% herb and 5% root (Echinaforce, Bioforce AG) is dosed as two tablets given three times daily.¹⁴¹² Another example is Echinacea purpurea herb juice. It's used in a daily dose of 6-9 mL. Tell patients that echinacea might modestly reduce cold symptoms if begun when symptoms are first noticed and continued for 7-10 days.

Elderberry (Sambucus nigra) might be useful for treating the flu. Elderberry has both antiviral and immunomodulating effects. Elderberry seems to increase production of inflammatory cytokines, such as interleukins and tumor necrosis factor. It also seems to prevent viral attachment to cells, similar to the neuraminidase inhibitors. Elderberry is active against both influenza A and B. The standardized elderberry extract, Sambucol, seems to shorten the duration of symptoms such as fever and myalgia when 4 tablespoons are taken daily for 3 days. Tell patients that elderberry might reduce flu symptoms.^5260,10796 Caution patients not to use uncooked elderberry fruit. The raw fruit contains toxic compounds.

Patients may ask about a homeopathic product, Oscillococcinum for preventing and treating the flu. The rationale for its use in influenza comes from the homeopathic principle of "like cures like." Oscillococcinum is made from very small doses of wild duck heart and liver, a well-known source for influenza viruses. There's no proof it prevents or treats influenza. Some researchers might claim it reduces duration, but analysis of the data shows only a one-fourth of a day reduction.¹⁰⁸⁰⁴ This is not significant. Tell patients not to waste their money.

One gram of vitamin C taken PROPHYLACTICALLY seems to reduce the duration of cold symptoms by about a half-day.⁶⁴⁵⁸ But these doses are associated with a greater incidence of adverse effects...nausea and diarrhea.⁴⁸⁴⁴ Taking 1 gram or 3 grams of vitamin C daily for two days at the ONSET of cold symptoms doesn't seem to have any effect on symptom severity or duration.⁹⁸³³ Tell patients the slight reduction in duration of cold symptoms isn't worth taking gram doses of vitamin C.

Research is divided on zinc for treating colds. A lot of research suggests that zinc lozenges providing 9-24 mg elemental zinc per dose begun within 24-48 hours of the onset of cold symptoms reduces the severity and duration of colds.^{333,334,335,336,337,6703,6705} But other research shows no effect.^{338, 339,6521,6522,6700} Tell adult patients zinc lozenges might be worth a try. But patients have to use a zinc lozenge every 2-3 hours while awake. Zinc may produce a dry or astringent feeling in the mouth.¹⁰⁸⁶⁴

Studies using zinc lozenges in children show conflicting conclusions.^341,10803 It's too soon to recommend zinc lozenges for children.

People also use zinc in nasal formulations. Zinc SULFATE nasal sprays don't seem to help cold symptoms.⁸⁶²⁹ Zinc GLUCONATE nasal gel (Zicam) in a total daily dose of 2.1 mg seems to lessen the severity and shorten the duration of cold symptoms by up to 75%.^6471,10247 But other evidence suggests it has no effect on cold symptoms.⁸⁶²⁸ Tell patients who want to try zinc gluconate nasal gel to begin using it within 24-48 hours of symptom onset and continue for the duration of cold symptoms.

Lots of other natural products are used to treat colds and flu...goldenseal, pau d'arco, astragalus, larch arabinogalactan, propolis, boneset, wild indigo, and Siberian ginseng. These products are marketed as "immune system supporters." They are used alone or in combination with other natural products, such as echinacea. But there's no reliable clinical evidence that they relieve cold symptoms. Theoretically, natural products that stimulate the immune system could exacerbate autoimmune diseases. They could also interfere with immunosuppressants, such as cyclosporine (Sandimmune).

Miscellaneous

Saline nasal sprays or drops are sometimes recommended as a benign cold treatment. But most studies using nasal irrigation are in patients with allergic rhinitis, sinusitis, or nasal surgery.¹¹¹⁰⁸ Two-percent saline doesn't seem to improve nasal symptoms in cold sufferers any better than normal saline (0.9%).¹¹¹⁰⁹ There are no studies showing saline nasal irrigation lessens the severity or shortens the duration of cold symptoms. Tell patients saline sprays don't seem to help cold symptoms.

Teas are often promoted for cold and flu symptoms. Elderflower, rose hip, goldenseal, German chamomile, peppermint, slippery elm,