Concerns about safety have focused on formaldehyde in part because high concentrations of formaldehyde can damage DNA (the building block of genes) and cause cancerous changes in cells in the laboratory. Although formaldehyde is diluted during the manufacturing process, residual quantities of formaldehyde may be found in several current vaccines (see table below). While formaldehyde is a likely cause of nasopharyngeal cancer, the quantities contained in vaccines are not sufficient to cause cancer. 

The average quantity of formaldehyde to which a young infant could be exposed to in the first two years of life may be as high as 0.7 – 0.8 mg (see table below). This quantity of formaldehyde is considered to be safe for two reasons:

• Formaldehyde is essential in human metabolism and is required for the synthesis of DNA and amino acids (the building blocks of protein). Therefore, all humans have detectable quantities of natural formaldehyde in their circulation (about 2.5 ug of formaldehyde per ml of blood). Assuming an average weight of a 2-month-old of 5 kg and an average blood volume of 85 ml per kg, the total quantity of formaldehyde found in an infant's circulation would be about 1.1 mg, a value about 1,500 times more than the amount an infant would be exposed to in any individual vaccine.
• Quantities of formaldehyde at least 600 times greater than the amount contained in vaccines have been fed safely to animals in drinking water.

Formaldehyde content of vaccines licensed for use in the United States

Td (adult)/ DT

Quantity per dose: ≤ 0.005 mg – 0.1 mg

DTaP (Daptacel, Infanrix)

Quantity per dose: ≤ 0.005 mg – ≤ 0.1 mg

DTaP-Hep B IPV (Pediarix)

Quantity per dose: ≤ 0.1 mg

DTaP-IPV (Kinrix, Quadracel)

Quantity per dose:

• Kinrix: ≤ 0.1 mg
• Quadracel: < 0.005 mg

DTaP-IPV-Hib (Pentacel)

Quantity per dose: < 0.005 mg

Hepatitis A (Havrix, Vaqta)

Quantity per dose:

• Havrix: ≤ 0.05 mg (pediatric), ≤ 0.1 mg (adult)
• Vaqta: 0.0004 mg (pediatric), 0.0008 mg (adult)

Hepatitis A - Hepatitis B (Twinrix)

Quantity per dose: ≤ 0.1 mg

Hib (ActHIB, HIBERIX)

Quantity per dose: < 0.005 mg

Hepatitis B (RECOMBIVAX)

Quantity per dose: < 0.0075 mg (pediatric); < 0.015 mg (adult and dialysis formulations)

Meningococcal vaccines

Meningococcal ACWY:

• Menactra  quantity per dose: < 0.00266 mg
• Menveo quantity per dose: < 0.0003 mg

Polio (IPOL)

Quantity per dose: ≤ 0.02%

Japanese encephalitis vaccine (IXIARO)

Quantity per dose: < 200 ppm

Tdap (ADACEL, Boostrix)

Quantity per dose:

• ADACEL: ≤ 0.005 mg
• Boostrix: ≤ 0.1 mg

Influenza

Not all influenza vaccines contain formaldehyde, but some preparations contain amounts between < 0.005 – 0.1 mg.

References

Mitkus RJ, Hess MA, Schwartz SL. Pharmacokinetic modeling as an approach to assessing the safety of residual formaldehyde in infant vaccines. Vaccine 2013;31:2738-2743. 
The authors estimated the levels of formaldehyde in blood and total body water following exposure to formaldehyde-containing vaccines and compared them with endogenous background levels. (Formaldehyde is a natural product of single-carbon metabolism.) Following a single intramuscular dose of 200 micrograms of formaldehyde, which is equivalent to the amount of formaldehyde received from DTaP, Hib, IPV, and hepatitis B at a single office visit, formaldehyde was completely removed from the site of injection within 30 minutes. Peak concentrations of formaldehyde in blood were estimated to be less than 1 percent of the level of formaldehyde naturally produced by the body. The authors concluded that formaldehyde in vaccines is safe.