Tag: anamnestic response

Why Are Vaccinated Australians Now Catching Measles?

Measles is on the rise in Australia, like many other places. But why are vaccinated Australians now catching measles?

More vaccinated Australians are catching measles because there is more measles in Australia.
More vaccinated Australians are catching measles because there is more measles in Australia.

And has this got folks thinking it is because the disease is evolving?

Why Are Vaccinated Australians Now Catching Measles?

Well, apparently it has some folks thinking that.

Remember, Andrew Wakefield has also been talking about mutant measles.

Is that what this story in Australia was about?

No.

“In recent years, 13 Victorians have been hospitalized with measles despite having one or two vaccinations that should have made them immune. Why? Well, experts believe that because measles is so rare in Australia, we pretty much never come into contact with it, so our immune systems are starting to let their guards down and wane a little bit.”

Nathan Templeton on Measles Immunity Concerns

What is he talking about?

It’s the idea of exogenous boosting from being around natural infections. In other words, after you become immune from being vaccinated, you could get a boost in your immune protection if you are around someone with the disease.

“The exogenous boosting (EB) hypothesis posits that cell-mediated immunity is boosted for individuals reexposed to varicella-zoster virus (VZV).”

Talbird et al on Understanding the role of exogenous boosting in modeling varicella vaccination.

While this is thought to happen with chickenpox, we aren’t sure if it happens with measles.

It might, but the “problem” is that it is known that folks can have an amnestic response, so can be immune even though they have low antibody levels.

Mostly though, it is important to keep in mind that most of the people who get measles are unvaccinated, often intentionally unvaccinated.

“The key to measles elimination is increasing vaccination coverage and monitoring of measles antibody status for all ages, as well as enhancing surveillance of both domestic and overseas incidences.”

Inaida et al on Measles elimination and immunisation: national surveillance trends in Japan, 2008-2015.

So how many vaccinated Australians are getting measles?

Overall, there are 154 cases of measles in Australia so far this year.

“In Australia, the majority of measles cases are due to unvaccinated individuals becoming infected while travelling to countries in which measles is either common or there are outbreaks occurring. As measles is highly contagious, these people can then spread the disease to others, causing outbreaks, often before they are aware that they have the virus.”

Australia’s Measles Outbreaks 2019

And just as in the United States and most other countries, most of their outbreaks are started by folks who are unvaccinated.

More on Measles in Australia

How Often Should You Do Vaccine Titer Testing?

We sometimes hear about folks doing vaccine titer testing.

A vaccine titer is a blood test that can determine whether or not you are immune to a disease after you get a vaccine.

While that sounds good, after all, why not check and be sure, it has downsides. Chief among them is that the results aren’t always accurate.

That’s right. You can sometimes have a negative titer test, but still be immune because of memory B cells and the anamnestic response.

How Often Should You Do Vaccine Titer Testing?

So how often should you do vaccine titer testing?

It depends, but most folks might never have it done!

Why not?

Vaccines work very well, so you would typically not need to routinely check and confirm that you are immune after being vaccinated. And, this is also important, the vaccine titer tests don’t always work that well, titer testing isn’t available for all vaccines (you can’t do titer testing for Hib and pertussis), and the testing can be expensive.

So we usually just do the testing (a quantitative titer) for folks that are in high risk situations, including:

  • pregnancy – rubella titer only (HBsAg is also done, but that’s not a vaccine titer test, but rather to see if you are chronically infected with hepatitis B)
  • healthcare workers – anti-HBs (antibody to the hepatitis B surface antigen to confirm immunity after being vaccinated)
  • students in nursing school and medical school, etc. – anti-HBs
  • children and adults exposed in an outbreakmeasles, chicken pox, mumps, etc., but only if we are unsure if they were previously vaccinated and protected
  • after a needlestick injury, etc. – to confirm immunity to hepatitis B
  • babies born to a mother with hepatitis B – to confirm that their hepatitis B vaccine worked

Vaccine titer testing might also be done for:

  • internationally adopted children – to confirm that they are immune if we unsure about all of the vaccines the child got in other countries
  • children and adults with lost vaccine records – to confirm that they are immune, since we are unsure about all of the vaccines they got
  • evaluation of children and adults with immune system problems – to help identify what immune system problems they might have – typically involves checking pneumococcal titers, giving Prevnar, and then checking pneumococcal titers again
  • people at continuous or frequent risk for rabies – rabies titer testing every 6 months to 2 years
  • patients with inflammatory bowel disease, before starting immunosuppressive therapy – hepatitis A and hepatitis B titers, as they might be at increased risk for hepatitis

While checking titers is easy, it is sometimes harder to know what to do with the results you get.

Of all of these different titers, only one tells you that you are immune due to vaccination.
Of all of these different titers, only one tells you that you are immune due to vaccination.

It is especially important to know that:

  • most people don’t need to have their titers checked routinely if they are not in one of the high-risk groups noted above
  • it isn’t practical to get titers tested as a method of potentially skipping one or more doses of your child’s vaccines, after all, if the titer is negative, then you are still going to have to get vaccinated
  • a healthcare provider with a negative measles titer after two doses of the MMR vaccine does not need another dose of vaccine
  • a healthcare provider who has anti-HBs <10 mIU/mL (negative titer) after three doses of the hepatitis B vaccine should get another dose of vaccine and repeat testing in 1 to 2 months – if still <10 mIU/mL, they should then get two more doses of hepatitis B vaccine (for a total of 6 doses) and repeat testing. If still negative, these documented nonresponders will need HBIG as post-exposure prophylaxis for any future hepatitis B exposures, but no further doses of hepatitis B vaccine.
  • vaccinated women of childbearing age who have received one or two doses of rubella-containing vaccine and have rubella serum IgG levels that is not clearly positive should be administered one additional dose of MMR vaccine, with a maximum of three doses, and should not be tested again
  • postvaccination titer testing is not recommended after the chicken pox vaccine
  • in addition to not being able to test titers for pertussis and Hib immunity, it is becoming difficult to test poliovirus type 2 titers, as the test uses a live virus that isn’t routinely available anymore (type 2 polio has been eradicated)

Still think you need vaccine titer testing?

More on Vaccine Titer Testing

Did Your Hepatitis B Antibody Test Come Back Negative?

Hepatitis B can be prevented.Three doses of the hepatitis B vaccines have been shown to provide long lasting protection in most people.

Do you need to get your titers checked to make sure you are immune?

Usually not. Simply being fully vaccinated with the  vaccine is  good enough evidence that you are immune in most, but not all circumstances.

A few circumstances in which you might need to be tested can include:

  • a baby who was born to a HBsAg (hepatitis B surface antigen) mother
  • being a healthcare worker who has a job and who is in a work setting that puts them at higher risk for exposure to blood or body fluids from patients who are positive for HBsAg
  • being immunocompromised, so you are not sure if the vaccine is going to work, or patients requiring chronic dialysis
  • someone who has sex or shares needles with a person who has a chronic hepatitis B infection

The screening test for vaccine immunity that is done checks the persons level of anti-HBs (antibody to the hepatitis B surface antigen). It should be done one to two months after your last dose of hepatitis B vaccine, but not later.

“Persons determined to have anti-HBs concentrations of ≥10 mIU/mL after receipt of the primary vaccine series are considered immune, and the result should be documented. Immunocompetent persons have long-term protection and do not need further periodic testing to assess anti-HBs levels.”

CDC on Immunization of Health-Care Personnel

The alternative to screening healthcare workers after they complete their vaccination series is to do postexposure management. In this method, in the case of a needlestick or other blood or body fluid exposure, both the source patient and the health care worker are tested and postexposure prophylaxis is given as necessary.

Don’t pregnant women get tested for hepatitis B? They do, but not to see if they are immune from immunization. They routinely have a HBsAg test to see if they have a chronic hepatitis B infection, which can be passed on to their baby.

Other screening tests that can be done include anti-HBc (antibody to hepatitis B core antigen) and IgM anti-HBc (IgM subclass to hepatitis B core antigen). These two tests can help you figure out if a person has an acute infection or is immune from a past infection.

Non-Immune Hepatitis B Titer Levels

Why check the anti-HBs level?

Because of the devastating effects of chronic hepatitis B infections, it is good to have all of the information you can get to help prevent a possible infection if you are exposed to blood or body fluids while working.

Having a positive anti-HBs level, typically defined as a level of ≥10 IU/mL, means that you are immune and protected.

But what if your level is negative? What if your level is <10 IU/mL after you have already gotten three doses of hepatitis B vaccine?

Then you get another dose of hepatitis B vaccine and the level is checked again in one to two months. If it is still <10 IU/mL, then you get two more doses of hepatitis B vaccine and the level is checked again in one to two months.

If you are still negative after six or more doses of hepatitis B vaccine, then you are considered a non-responder. You would then require postexposure testing and possible prophylaxis if you are exposed to a patient’s blood or body fluids.

What If You Lost Your Hepatitis B Immunity?

There is a reason that they don’t recommend testing more than one to two months after your last dose of hepatitis B vaccine.

“Studies indicate that immunologic memory remains intact for at least 20 years and confers protection against clinical illness and chronic HBV infection, even though anti-HBs levels that once measured adequate might become low or decline below detectable levels. If one is challenged with HBV, people whose immune systems are competent will mount an anamnestic response and develop protective anti-HBs.”

Immunization Action Coalition on Hepatitis B Questions

It is known that anti-HBs levels can decrease over time.

Fortunately, this does not lead to waning immunity in typical circumstances. Because of an anamnestic response, the hepatitis B vaccine provides long lasting protection, even if your antibody levels appear to have dropped.

Avoiding Hepatitis B

Since health care workers should practice universal precautions whether or not they are immune to hepatitis B, being a non-responder isn’t going to change how you do things too much.

Plus, there are other diseases that are not yet vaccine preventable that you could get if you are stuck with a needle, so you are hopefully still very careful, no matter how immune you are to hepatitis B.

Still, it is very nice to have one less thing to worry about in this situation.

“Unvaccinated or incompletely vaccinated persons who experience a workplace exposure from persons known to be HBsAg-positive should receive 1 dose of hepatitis B immune globulin HBIG (i.e., passive vaccination) as soon as possible after exposure (preferably within 24 hours).”

CDC on Immunization of Health-Care Personnel

If you are a non-responder and and are exposed to hepatitis B, then one thing that is different is that you will likely require two doses of HBIG (hepatitis B immune globulin) for protection. Others can get one dose of HBIG and can repeat the hepatitis B vaccine. Those who are fully vaccinated and known to be immune likely won’t have to do anything to protect themselves from hepatitis B, although each incident should be investigated to make sure.

But it is not just healthcare workers who are at risk for accidental needlesticks. What if a healthcare worker sticks themselves and then you or your child? Or what if your child gets stuck with a discarded needle at the park?

What to Know About Hepatitis B Titers

Get vaccinated and follow the latest guidelines if you are exposed to hepatitis B, especially if you are a non-responder to the vaccine with low titer levels.

More on Hepatitis B Titers and Immunity

Vaccine Titer Testing

Titer testing, laboratory evidence of immunity, is available for some vaccines and in some situations.

Vaccine Titer Testing

With titer testing, you do a blood test to check your antibody levels, which can help determine if you are immune to a specific disease, like measles or chicken pox.

Vaccine titer testing is available to confirm your immunity for some vaccine-preventable diseases.
Vaccine titer testing is available to confirm your immunity for some vaccine-preventable diseases.

Titer testing is sometimes recommended to confirm the immunity status of:

  • healthcare workers
  • pregnant women – rubella and hepatitis B
  • internationally adopted children
  • children and adults with lost vaccine records

While not available for all vaccines, like Hib and pertussis, when necessary, you can check titers for MMR, hepatitis A, hepatitis B, diphtheria, tetanus, and varicella.

Should you get titer testing just in case your child is immune from an asymptomatic infection? While it is true that many viruses and bacteria can cause infections without symptoms, it is extremely unlikely that your child would have had a vaccine-preventable disease without symptoms, considering most are at low levels.

Titer testing to avoid a second MMR vaccine is also not recommended. Although the second MMR vaccine is technically not a booster shot, if your child is negative to any of the three components of the vaccine, then he will still need the second shot.

Is there a downside to doing vaccine titer tests?

“Commercial antibody assays, particularly the LA test, may not be sensitive enough to detect vaccine-induced antibody in some recipients.

Because of the potential for false-negative serologic tests, routine postvaccination serologic testing is not recommended.”

Immune response to varicella vaccine: infection versus vaccine response

Many people who have negative titer tests may still be immune because they have a retained anamnestic potential, instead of being a nonresponder to the vaccine or losing their immunity.

And then there is the pain and cost of doing a blood test.

Also, if titer testing is negative, even if it is a false-negative, you will have to get a vaccine anyway, which is why most doctors and parents opt for getting kids vaccinated and skipping titer testing unless it is necessary.

More on Vaccine Titer Testing