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There is no way to prevent a cold once exposed to the virus. Some strains of flu (influenza) may be prevented via vaccine and certain medications. People with a cold or flu are encouraged to stay home, rest and avoid passing the infection to others.

One of the easiest ways to prevent transmission of a cold or flu virus is by practicing good hygiene. This includes washing one’s hands after coughing or sneezing, or after coming into contact with a person with a viral infection. It is also important to cover the nose and mouth when sneezing or coughing. The spread of a virus can also be prevented by not sharing items such as towels, eating utensils, bottles or beverage containers with others. Tissues should be promptly disposed of after use, and hands should be washed after handling used tissues.

It may be difficult to completely avoid contact with infected persons. Some people with viral infections may be contagious before any signs of illness appear – although people are most contagious during the first two to four days after symptoms appear, according to the American Academy of Family Physicians (AAFP). Some people may continue to be contagious for up to three weeks.  

Controversy surrounds some popular over-the-counter medications believed to help prevent viral infection. Parents should consult their child’s pediatrician before providing any herbal remedies or exceeding the recommended daily allowance of any vitamin or supplement. These controversial preventive methods include:

• Vitamin C. There is no conclusive evidence that vitamin C prevents viral infections.
  
  
• Zinc. Studies have shown inconsistent results – anywhere from no change to dramatic benefits – from the use of zinc on cold or flu symptoms.
  
  
• Echinacea. The effectiveness of Echinacea to prevent viral infections has not been adequately studied. The lack of a standard formula within commercial products containing Echinacea makes it difficult to scientifically evaluate.

Because fewer varieties of flu viruses exist than cold viruses, a vaccine is available for the flu. Every year, a flu vaccine is developed to prevent three specific strains of flu expected to occur that year. The vaccine is usually given as a shot in the upper arm. This exposes patients to dead flu viruses, helping the body to develop an immunity or resistance to those particular viruses. It may also help those who contract different strains of the flu to have less severe symptoms. Side effects of the flu shot include soreness where the shot was provided, muscle aches and fever.

The vaccine is also available in nasal spray form, sometimes referred to as LAIV (live attenuated influenza vaccine). This is because it contains live but weakened flu viruses. Side effects of the nasal spray vaccine include a runny nose, headache, cough and sore throat.

Flu vaccines are considered 70 to 90 percent effective in preventing the flu caused by the specific strains contained in the vaccine in healthy people under the age of 65 years, according to the AAFP. Protection lasts for one year, since viruses are constantly changing and new strains must be identified for inclusion in the vaccine.

It is not possible to contract the flu from the vaccine. Flu vaccines are usually provided in the fall, although they may be obtained any time during the flu season (November through April). It can take one to two weeks for the body to build up immunity to the flu viruses contained in the vaccine. Parents should check with their child’s pediatrician before getting a vaccine for their child.

Flu vaccines are recommended for the following groups who are at risk of complications as a result of the flu:

• Caregivers and parents of infants less than 6 months old. Colds and the flu can be dangerous to very young children, since these viral infections may quickly develop into more serious conditions (e.g., pneumonia) in this population.
  
  
• Young children. The Centers for Disease Control and Prevention (CDC) recommends that children ages 6 months to 59 months old receive a flu shot every year. Nasal spray vaccines are not recommended for children under the age of 5 years old.
  
  
• Children and teens on chronic aspirin therapy. It is recommended that all children (age 6 months to 18 years) who take aspirin regularly receive the flu shot, because of the risk of Reye syndrome. The nasal spray is not recommended for this population.
  
  
• Adults and children ages 6 months and older with any of the following chronic health conditions:
  
  
• Weakened immune systems.
• Heart or lung disorders, including asthma.
• Metabolic diseases, such as diabetes, kidney disease and hemoglobin (a protein component of red blood cells that gives blood its color) abnormalities.
• Older adults (65 years and older). It is recommended that this age group receive the flu shot (not nasal spray) vaccine.
  
• Pregnant women. The flu shot is safe and recommended for women who are pregnant or breastfeeding. But, they should not receive the nasal spray form.
  
• Residents of nursing homes or long-term care facilities.
  
  
• Healthcare workers.
  
  
• Anyone living with lots of other people (e.g., large families, shelters after a natural disaster).

Anyone with the following conditions should not get a flu vaccine without first consulting with a physician:

• Allergy to eggs (flu vaccines are grown inside eggs)
  
  
• Allergy to prior flu shots
  
  
• Moderate or severe illness with a fever
  
  
• History of Guillain-Barre syndrome (a rare, acute illness causing progressive muscular weakness and difficulty breathing)
  

If flu vaccines are in short supply (usually the result of distribution delays rather than an actual shortage), the CDC may recommend that certain high-risk populations get the shot first.