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Issue 1,685: April 4, 2023
Ask the Experts: As seen on social media now regularly features both written and short video versions of clinical questions and answers (Q&As) from our popular Ask the Experts section on our social media channels: YouTube, Instagram, Facebook, Twitter, and LinkedIn. This issue introduces you to three of our new Ask the Experts videos, plus a selection of 7 Q&As recently shared on social media. Follow on your preferred social media channels for posts that make it easier for you to improve your vaccination practices a little every day.

Because COVID-19 vaccination recommendations and clinical guidance are updated frequently, reminds our readers to regularly visit CDC’s web page: Use of COVID-19 Vaccines in the United States.

You can also find these Q&As and more than a thousand other Q&As about vaccines and vaccine administration on our “Ask the Experts” main page at’s team of experts includes Kelly L. Moore, MD, MPH (team lead), Carolyn B. Bridges, MD, FACP, and Iyabode Beysolow, MD, MPH.
Video Q&As

Video Q&As

Q: How late in the season can I vaccinate patients with influenza vaccine?

A: Peak influenza activity generally occurs in the Northern Hemisphere in January or February. Providers should continue vaccinating patients through spring, as long as there is continued circulation of influenza viruses and they have unexpired vaccine in stock and unvaccinated patients in their office.

Because influenza occurs in many areas of the world during April through September, vaccine should be given to travelers who missed vaccination in the preceding fall and winter. Another late season use of vaccine is for children younger than age 9 years who needed 2 doses of vaccine but failed to get their second dose early in the season. For each of these situations, vaccine can be given through the month of June since most injectable influenza vaccine has a June thirty expiration date.

Q: What’s the difference between a contraindication and a precaution?

A contraindication is a condition in a recipient that increases the risk for a serious adverse reaction to vaccination and is a condition under which vaccines should not be administered. In addition to contraindications found in prescribing information, ACIP may recommend against the use of a vaccine under certain conditions, such as a lack of data about use of a vaccine in a specific situation, such as pregnancy.

A precaution is a condition in a recipient that might increase the risk for a serious adverse reaction, might cause diagnostic confusion, or might compromise the ability of the vaccine to produce immunity. For example, not vaccinating a person who is moderately or severely acutely ill avoids diagnostic confusion between the underlying illness and side effects of vaccination. Vaccination may be deferred if a precaution is present, although a vaccination might be indicated in the presence of a precaution if the benefit of protection from the vaccine outweighs the risk for an adverse reaction.

Q: We frequently see patients who are febrile or have an acute illness and are due for vaccinations. We are uncertain if we should withhold the vaccines or not. What do you advise?

A: A “moderate or severe acute illness" is a precaution for administering any vaccine. A mild acute illness (such as diarrhea or mild upper respiratory tract infection) with or without fever is not a precaution, and vaccines may be given.

The concern in vaccinating someone with moderate or severe illness is that a fever following the vaccine could complicate management of the concurrent illness—it could be difficult to determine if the fever was from the vaccine or due to the concurrent illness. In deciding whether to vaccinate a patient with moderate or severe illness, the clinician needs to determine if deferring vaccination will increase the patient’s risk of vaccine-preventable diseases, as is the case if the patient is unlikely to return for vaccination or to seek vaccination elsewhere.

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Recent Social Media Q&As

Q: How does CDC define being “up to date" on COVID-19 vaccination?

A: CDC has used the term "fully vaccinated" to refer to people who have completed a primary COVID-19 vaccine series. CDC uses the term “up to date" (UTD) to refer to a person who has received all doses recommended for their age and health status. With the exception of children age 6 months through 4 years who have completed a 3-dose primary series with Pfizer-BioNTech COVID-19 Vaccine, for whom no booster dose is recommended, all other people age 6 months and older are considered UTD if they have completed a primary series and have received a bivalent COVID-19 booster dose. The definition of up-to-date vaccination of each age group is available here:

Q: May I use Novavax COVID-19 protein subunit vaccine as a booster dose?

A: Yes, but only in limited circumstances. Patients age 18 years or older who have completed any COVID-19 vaccine primary series, but who have never received a booster dose, may be offered a single Novavax monovalent COVID-19 vaccine as a booster dose under one of the following conditions: (1) the recommended bivalent mRNA vaccine is contraindicated, or (2) the patient refuses the recommended bivalent mRNA vaccine booster dose (or it is unavailable) and would not otherwise be vaccinated. The Novavax monovalent vaccine is not authorized for use as a booster dose in a person who has received one or more COVID-19 vaccine booster doses in the past.

Q: What proof do I need for COVID-19 vaccination of a patient who says he is moderately or severely immunocompromised?

A: CDC states that no additional medical documentation is required before vaccination. People may simply affirm that they are moderately or severely immunocompromised and receive COVID-19 vaccine doses wherever vaccines are offered. Vaccinators should not deny COVID-19 vaccination to a person due to lack of documentation.

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Q: Does CDC recommend restarting the hepatitis B vaccine series in the event the series is interrupted?

A: No. The series should not be restarted. Continue the series from where you left off.

Q: Several physicians in our group have no documentation showing they received hepatitis B vaccine. They are relatively sure, however, that they received the doses many years ago. What do we do now?

A: Because there is no documentation of vaccination, a vaccination series should be administered and postvaccination testing should be performed 1–2 months after the final dose of vaccine. There is no harm in receiving extra doses of vaccine. Postvaccination anti-HBs testing results should also be documented, including the date testing was performed. All healthcare settings should develop policies or guidelines to assure valid hepatitis B immunization.

Q: I'm a nurse who received the HepB series more than 10 years ago and had a positive follow-up titer (at least 10 mIU/mL). At present, my titer is negative (less than 10 mIU/ mL). What should I do now?

A: Do nothing. Data show that vaccine-induced anti-HBs levels might decline over time; however, immune memory (anamnestic anti-HBs response) remains intact following immunization. People with anti-HBs concentrations that decline to less than 10 mIU/mL are still protected against HBV infection. For healthcare professionals with normal immune status who have demonstrated adequate anti-HBs (at least 10 mIU/ mL) following full vaccination, booster doses of vaccine or periodic anti-HBs testing are not recommended.

Q: If dose #1 of HPV vaccine was given before the 15th birthday and it has been more than a year since that dose was given, would the series be complete with just one additional dose?

A: Yes. Adolescents and adults who started the HPV vaccine series prior to the 15th birthday and who are not immunocompromised are considered to be adequately vaccinated with just one additional dose of HPV vaccine.

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IZ Express is supported in part by Grant No. 1NH23IP922654 from the National Center for Immunization and Respiratory Diseases, CDC. Its contents are solely the responsibility of and do not necessarily represent the official views of CDC.

IZ Express Disclaimer
ISSN 2771-8085

About IZ Express

IZ Express is supported in part by Grant No. 1NH23IP922654 from CDC’s National Center for Immunization and Respiratory Diseases. Its contents are solely the responsibility of and do not necessarily represent the official views of CDC.

IZ Express Disclaimer
ISSN 2771-8085

Editorial Information

  • Editor-in-Chief
    Kelly L. Moore, MD, MPH
  • Managing Editor
    John D. Grabenstein, RPh, PhD
  • Associate Editor
    Sharon G. Humiston, MD, MPH
  • Writer/Publication Coordinator
    Taryn Chapman, MS
    Courtnay Londo, MA
  • Style and Copy Editor
    Marian Deegan, JD
  • Web Edition Managers
    Arkady Shakhnovich
    Jermaine Royes
  • Contributing Writer
    Laurel H. Wood, MPA
  • Technical Reviewer
    Kayla Ohlde

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