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Scheduling Vaccines

Ask the Experts: Topics

Scheduling Vaccines

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Scheduling Vaccines
Why are vaccines generally not given to infants younger than 6 weeks of age in the U.S.?
Mainly because little safety or efficacy data exist on doses given before 6 weeks of age, and the vaccines aren't licensed for this use. The data that exist suggest that the response to doses given before 6 weeks is poor and in some cases (such as Haemophilus influenzae type b vaccine) the response could be detrimental to the infant by possibly reducing the immune response to subsequent doses of Hib conjugate vaccine. Hepatitis B vaccine is an exception because infants respond adequately to this vaccine as early as the day of birth and early receipt of this vaccine is necessary to protect infants born to HBsAg-positive mothers.
Is it necessary to start a vaccine series over if a patient doesn't come back for a dose at the recommended time, even if there's been a year or more delay?
For routinely administered vaccines, there is no vaccine series that needs to be restarted because of an interval that is longer than recommended. In certain circumstances, oral typhoid vaccine (which may be given for international travel) needs to be restarted if the vaccine series isn't completed within the recommended time frame.
What is meant by "minimum intervals" between vaccine doses?
Vaccination schedules are generally determined by clinical trials, usually prior to licensure of the vaccine. The spacing of doses in the clinical trial usually becomes the recommended schedule. A "minimum interval" is shorter than the recommended interval between doses, and is the shortest time between two doses of a vaccine series in which an adequate response to the second dose can be expected. The concern is that a dose given too soon after the previous dose may reduce the response to that dose. The minimum spacing between doses is generally included in the ACIP recommendation for that vaccine which can be found at www.cdc.gov/vaccines/hcp/acip-recs/index.html. In addition, an extensive listing of recommended and minimum intervals and ages for vaccination can be found in the ACIP General Recommendations on Immunization, available at www.cdc.gov/mmwr/pdf/rr/rr6002.pdf, pages 36-37.
How can we quickly determine how to "catch up" children who have fallen behind on their shots?
As a general rule, infants or children who are more than 1 month or 1 dose behind schedule should be on an accelerated schedule, which means the intervals between doses should be reduced to the minimum allowable. Catch-up schedules for children ages 4 months through 18 years are included with each year's recommended immunization schedule that is issued by ACIP, AAP, and American Academy of Family Physicians (AAFP). To obtain a copy, go to www.cdc.gov/vaccines/schedules/hcp/index.html.
When a 3-month-old infant presents having had no prior immunizations, would you start the accelerated schedule?
The accelerated schedule should be used when the child is more than a month behind schedule, until you get them caught up. An accelerated schedule is acceptable as long as minimum ages and minimum intervals are observed for each dose. Once you have the child back on schedule, use the recommended ages and intervals on the childhood schedule. In this case you can give the child the first set of recommended vaccines at age 3 months and then bring him back at age 4 months and give the second set of vaccinations. At this point the child will be caught up and can return to the usual schedule. Be sure to educate the parents and talk to them about the importance of bringing the child back on time.
If two live virus vaccines are inadvertently given less than 4 weeks apart, what should be done?
If two live virus vaccines are administered less than 4 weeks apart and not on the same day, the vaccine given second should be considered invalid and repeated. The repeat dose should be administered at least 4 weeks after the invalid dose. Alternatively, one can perform serologic testing to check for immunity, but this option may be more costly, may not be practical if multiple antigens are involved (such as measles, mumps and rubella), and may provide results that are difficult to interpret.
We gave a dose of vaccine too soon after the previous dose. When can we give another (valid) dose?
If vaccines are given too close together, it can result in a less than optimal immune response. However, in most instances, a difference of a few days is unlikely to have a negative effect on immune response. With the exception of rabies vaccine, ACIP allows a grace period of 4 days (i.e., vaccine doses administered up to 4 days before the recommended minimum interval or age can be counted as valid). However, if a dose was administered 5 or more days earlier than the recommended minimum interval between doses, it is not valid and must be repeated. The repeat dose should be spaced after the invalid dose by the recommended minimum interval.
If the first dose in a series is given 5 days or more before the recommended minimum age, the dose should be repeated on or after the date when the child reaches at least the minimum age. If the vaccine is a live vaccine, ensuring that a minimum interval of 28 days has elapsed from the invalid dose is recommended. Avoid such errors by knowing the minimum intervals and ages for routinely given vaccines. You can look up such information www.cdc.gov/mmwr/pdf/rr/rr6002.pdf, pages 36-37.
The 4-day "grace period" should not be used when scheduling future vaccination visits, and should not be applied to the 28-day interval between live parenteral vaccines not administered at the same visit. It should be used primarily when reviewing vaccination records (for example, when evaluating a vaccination record prior to entry to daycare or school).
For the purpose of vaccine spacing, what constitutes a month: 28 days (4 weeks), 30 days, or 31 days?
For intervals of 3 months or less, you should use 28 days (4 weeks) as a "month." For intervals of 4 months or longer, you should consider a month a "calendar month": the interval from one calendar date to the next a month later. This is a convention that was introduced on the childhood schedule in 2002 and discussed in the paper "Evaluation of Invalid Vaccine Doses" (Stokley S, Maurice E, Smith PJ, et al. American Journal of Preventive Medicine, 2004: 26[1]: 34–40).
We sometimes have differences of opinion among our staff in determining the minimum interval or age for administering vaccines. Recommendations are sometimes written in months, weeks, or days. Can you help clarify?
Customarily, if the dosing interval is 4 months or more, it is common to use calendar months (e.g., 6 months from October 1 is April 1). If the interval is less than 4 months, it is common to convert months into days or weeks (e.g., 1 month = 4 weeks = 28 days).
A 3-year-old who was otherwise on schedule received some of her 15-month vaccinations (MMR, DTaP, IPV) twice due to a change in health plans. Can these doses be counted toward kindergarten vaccinations?
Whether these doses count as part of the child's series depends on the intervals between these doses and the ones that preceded them. If the second MMR was separated from the previous one by at least 4 weeks, it can be counted as the second MMR. No additional doses are indicated. The 4th dose of IPV is recommended after the 4th birthday. In this case, the child would need a fifth dose of IPV on or after her fourth birthday. The fifth dose of DTaP should not be given earlier than age 4 years. Assuming this dose of DTaP was the fifth the child received, it was given much too early and should not be counted. The DTaP should be repeated on or after the child's fourth birthday.
If I give a pneumococcal polysaccharide vaccine to my patient now, how long must I wait before giving the influenza or Td vaccine?
Influenza vaccine and Td (or Tdap) may be given at the same time or at any time before or after a dose of pneumococcal polysaccharide vaccine. The only time you have to wait is when two LIVE vaccines are not given at the same visit; then you need to wait at least 4 weeks to give the second live vaccine.
Why can zoster vaccine be given without a delay after receipt of a blood product but a delay of up to a year is recommended for varicella vaccine?
This difference is due to the larger amount of varicella vaccine virus in zoster vaccine. In the zoster vaccine clinical trials all the participants had had varicella and were immune. So their pre-existing immunity (and the amount of antibody expected to be in most blood products) did not blunt their response to the vaccine. Varicella vaccine has a lower dose of varicella virus and is given to susceptible people. Passively-acquired antibody may interfere with the response to low-dose varicella vaccine for up to a year depending on what product is given.
What interval should be observed between receipt of a blood product and vaccination with live attenuated influenza vaccine (LAIV)?
LAIV can be administered at any time before or after receipt of a blood product. See www.cdc.gov/mmwr/pdf/rr/rr6002.pdf, pages 9 and 38-39.
This page was reviewed on May 1, 2014
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This website is supported in part by a cooperative agreement from the National Center for Immunization and Respiratory Diseases (Grant No. 5U38IP000290) at the Centers for Disease Control and Prevention (CDC) in Atlanta, GA. The website content is the sole responsibility of IAC and does not necessarily represent the official views of CDC.