Vaccines

Vaccines are biological products given as injections, nasal sprays, or oral drops. They stimulate the immune system by exposing it to controlled amounts of weakened or dead microbes, or to specific components of those microbes. The immune system responds by producing protective antibodies. Vaccines provide active immunity.

Most vaccines (including inactivated vaccines and the live nasal spray influenza vaccine) are stored refrigerated. Some vaccines, such as the chickenpox (varicella) vaccine, VARIVAX, and the Zostavax shingles vaccine, are stored frozen. The Pfizer COVID-19 vaccine is stored (before thawing) in an ultracold freezer between -80 to -60 degrees Celsius. If a frozen vaccine needs to be prepared, it should be slowly defrosted in a refrigerator.

Before administering a vaccine, the lot number, expiry date, and manufacturer are recorded, and a vaccine information statement (VIS) is given to the patient.

Depending on the vaccine components and the immune response they produce, vaccines can be classified as follows:

Vaccine type	Description	Examples
Live attenuated	- Uses an attenuated or weakened strain of the microorganism

• Stimulates cell-mediated, long-lasting immunity
• Temperature sensitive
• Contraindicated in immunocompromised individuals like HIV, organ transplant recipients, etc. | MMR
  Rotavirus
  Smallpox
  Chickenpox
  Yellow fever
  Nasal influenza
  Oral polio (Sabin) | | Inactivated | - Use killed microorganisms
• Booster doses are essential for long-lasting immunity | Hepatitis A
  Flu shots
  Polio shots (IPV or Salk)
  Rabies | | Subunit, recombinant, polysaccharide, and conjugate | - Use antigenic parts or subunits of the pathogen to induce specific immunity
• Booster doses are required | Haemophilus influenzae type b or Hib
  Hepatitis B
  HPV
  Pertussis component of DTaP
  Pneumococcal
  Meningococcal
  Shingles
  Novavax for COVID-19 virus | | Toxoid | - Uses inactivated toxins | Diphtheria and Tetanus | | Messenger RNA (mRNA) vaccine | - Uses messenger RNA coding for protein like S protein in the COVID-19 virus | COVID-19 vaccines (Comirnaty, Moderna, Spikevax) | | Vector vaccines | - Uses a harmless vector like a non-pathogenic virus to introduce an antigenic protein into the body | COVID-19 vector vaccine from Janssen/Johnson and Johnson |

Vaccine adverse effects include fever, local erythema and swelling after DTaP booster doses, and allergic reactions to neomycin in MMR, IPV, and chickenpox vaccines. Influenza vaccine is contraindicated in serious egg allergies. Thimerosal is a mercury containing preservative used in some vaccines and can be potentially toxic to the developing brain of infants.

CDC immunization schedule for under 18 years of age: The recommended immunization schedule for children includes the Hepatitis B vaccine administered at birth, followed by boosters at 1 and 6 months of age, and a third dose at 18 months. Rotavirus vaccines are given in 2 doses between 2-4 months. Diphtheria, tetanus and acellular pertussis or DTaP, pneumococcal conjugate vaccine PCV 15 or 20, and inactivated polio vaccine are given as 4 separate doses typically in 2,4,6 months, followed by 9-15 months of age. An additional dose of DTaP and IPV is given between 4-6 years of age. At ages 10-12, a Tdap vaccine is administered. Haemophilus influenzae type b (Hib) vaccine is given in 3 or 4 doses, the first two doses in months 2 and 4, and the third or fourth doses between 9-15 months. Influenza vaccines are administered annually in the flu season. The first dose of MMR and Varicella vaccines is given between 12-15 months, and the second dose is between 4-6 years of age. Meningococcal vaccines are given at age 11-12 years and 16 years of age.

CDC recommended vaccines in adults: Certain vaccinations are recommended by CDC to prevent diseases like herpes zoster, pneumococcal pneumonia, severe flu, and COVID-19 pneumonia in susceptible adults. Shingles or herpes zoster vaccination, called RZV (recombinant zoster vaccine) or Shingrix, is given as 2 doses 2-6 months apart after the age of 50 years. HPV vaccine is administered in 2-3 doses depending on the initial age at immunization, starting at age 9 years.

Route of administration	Type of patient	Needle gauge and length*
Intramuscular	Neonate (up to 28 days of age)	22-25 G; ⅝ inch
Intramuscular	Infants (1-12 months of age)	22-25 G: 1 inch
Intramuscular	Children** (2-18 years of age)	22-25 G; 1-1.25 inches for injection into the thigh; ⅝-1 inch for injection into the arm
Intramuscular	Adults	22-25 G; 1 inch
For obese adults, use 1.5 inches
Subcutaneous	Any	23-25 G; ⅝ inch

*Needle gauge is denoted by G, which refers to the diameter of the hole in the needle. A higher G means a thinner needle. Needles are available in various gauges and lengths. The length is listed along with the gauge of the needle on the packaging.

**The arm is the preferred site for vaccinating older children (above 2 years of age), while the thigh is the preferred site for toddlers aged 1-2 years. Arm injection is recommended for adults.