Tag: serotypes

Dengvaxia for Dengue Fever

Dengvaxia was recently approved by the FDA after being available in other countries since about 2015.

“Indicated for the prevention of dengue disease caused by dengue virus serotypes 1, 2, 3 and 4. DENGVAXIA is approved for use in individuals 9 through 16 years of age with laboratory-confirmed previous dengue infection and living in endemic areas.”

Wait.

Dengue is endemic throughout the tropics and subtropics, including most of the Caribbean.
Dengue is endemic throughout the tropics and subtropics, including most of the Caribbean.

It’s only for people who have already had a dengue infection before?

Dengvaxia Controversy

Unfortunately, Dengvaxia “performs differently in seropositive versus seronegative individuals.”

“In areas of 70% dengue seroprevalence, over a 5-year follow-up, for every 4 severe cases prevented in seropositive, there would be one excess severe case in seronegative per 1,000 vaccinees; for every 13 hospitalizations prevented in seropositive vaccinees, there would be 1 excess hospitalization in seronegative vaccinees per 1,000 vaccinees.”

WHO on Questions and Answers on Dengue Vaccines

If you have never had dengue before and you are vaccinated, you are at risk for a severe infection if you do get dengue. On the other hand, if you are unvaccinated, you are at even greater risk of getting dengue, a life-threatening infection. Fortunately, the first episode of dengue is usually fairly mild.

The problem occurs if your antibody levels have dropped enough, which can cause you to have a severe case of dengue the second time. The process is called antibody-dependent enhancement and has to do with antibody levels, either natural or vaccine induced. So it can occur whether or not you are vaccinated, although getting Dengvaxia, an attenuated, live vaccine, can act as a primary dengue infection.

“These differing epidemiological features support the conclusion that antibody dependent enhanced (ADE) dengue disease occurred in seronegatives who were sensitized by vaccine. As hospitalizations continue to occur in all age groups Dengvaxia consumers should be warned that sensitized vaccinated seronegatives will experience enhanced dengue disease into the forseeable future.”

Scott Halstead on Dengvaxia sensitizes seronegatives to vaccine enhanced disease regardless of age.

It is something that dengue researcher Scott Halstead warned folks about as soon as he saw the first published study on Dengvaxia.

But why would you need a vaccine if you have already had dengue?

“In humans recovery from infection by one dengue virus provides lifelong immunity against that particular virus serotype. However, this immunity confers only partial and transient protection against subsequent infection by the other three serotypes of the virus. Evidence points to the fact that sequential infection increases the risk of developing severe dengue.”

WHO on Dengue control

There are four serotypes of dengue.

So if you aren’t vaccinated, you are at risk to get dengue multiple times.

Tragically, about 800,000 children in the Philippines were given Dengvaxia in a universal immunization program without checking to see if they had dengue first. And it likely led to some severe cases of dengue and deaths. This led to the vaccine being banned in that country and is thought to be one of the causes behind their current measles outbreak, as their Dengvaxia controversy led to more vaccine hesitancy.

And it will lead to more folks getting dengue. Instead of a ban, they should likely be more picky about who they give the vaccine to, either confirming that recipients have already had dengue (titer test) or only giving the vaccine to older kids.

Dengvaxia for Dengue Fever

Do you need Dengvaxia?

Remember, Dengvaxia is only for those living in endemic areas and in the United States, dengue is only endemic in the U.S. territories of American Samoa, Guam, Puerto Rico, and the U.S. Virgin Islands.

Do you need Dengvaxia if you are simply traveling to one of these areas?

Since Dengvaxia is not approved for those who haven’t had a dengue infection before, you likely wouldn’t get it just for traveling to an endemic area, unless perhaps you routinely travel to an endemic area and have had dengue already. A titer test can confirm a previous dengue infection, but there is no indication to get vaccinated for travel yet.

Also, while in other countries it is available for use between 9 and 45 years, in the United States, Dengvaxia is only approved for children between 9 and 16 years of age.

More on Dengvaxia for Dengue Fever

Is a Vaccine Strain Causing The Latest Measles Outbreak?

What’s the first question anti-vaccine folks start asking whenever we see a large outbreak of measles?

No, it’s not how can I get my kids vaccinated and protected so that they don’t get measles…

It is whether or not it a vaccine strain of measles started the outbreak.

That’s not how any of this works…

Where do folks get all of this stuff about genotypes and vaccine strains? I wonder…

Dr. Bob had no facts, but still posted that a vaccine strain of measles could have killed a woman who got caught up in the last measles outbreak in Washington.

Yup.

The usual suspects.

Is a Vaccine Strain Causing The Latest Measles Outbreak?

Why do folks who intentionally don’t vaccinate their kids desperately want these measles outbreaks to be caused by a vaccine strain?

Because then it isn’t their fault that their kids are at risk of getting a life-threatening disease!

It’s never a vaccine strain though.

Remember the Disneyland measles outbreak. A lot of folks were talking about vaccine strains when it first started.

“…California patients were genotyped; all were measles genotype B3, which has caused a large outbreak recently in the Philippines…”

Measles Outbreak — California, Dec 2014–Feb 2015

It wasn’t a vaccine strain.

OutbreaksYearGenotype
Minnesota2017B3
Tennessee2016B3
California2015B3
Florida2013D8
California2014B3, D8
Brooklyn2013D8
North Carolina2013D8
Minnesota2011B3
Washington, Illinois2008D5, D4

For example, during 2011, 222 cases of measles and 17 outbreaks were reported in the United States, with most cases originating from just five countries (France, Italy, Romania, Spain, and Germany). Six different genotypes were identified, including B3, D4, G3, D8, H1, and D9. No vaccine strains…

And no, it doesn’t matter that the vaccine strain of measles, genotype A, differs from all of the wild strains of measles we see in the outbreaks.

“Vaccine induced immunity protects against all virus strains. Measles is considered a monotypic virus despite the genetic variations.”

Factsheet about measles

Unlike the flu, HPV, and pneumococcal bacteria, in which vaccines only protect against different serotypes, in the case of measles, the genotype simply helps us figure out where the measles case came from.

And no, the latest outbreak, wherever it is, wasn’t caused by shedding from a vaccine.

But if it isn’t the vaccine strain, then why do they that is it important to rapidly identify wild strains vs vaccine strains?

“During measles outbreaks, it is important to be able to rapidly distinguish between measles cases and vaccine reactions to avoid unnecessary outbreak response measures such as case isolation and contact investigations.”

Roy et al on Rapid Identification of Measles Virus Vaccine Genotype by Real-Time PCR

That’s easy to answer.

Outbreaks typically trigger a lot of folks to get vaccinated. While that’s great, one possible problem is that some of those folks might develop a fever and/or rash after their MMR vaccine. So it is important to quickly figure out whether they are part of the outbreak and have a wild strain (maybe they were exposed before their vaccine could start to work) or are having a common, mild vaccine reaction.

But couldn’t they have vaccine-associated measles if they have a rash and fever and a vaccine strain? Theoretically, but then they would likely have true measles symptoms. And even in these rare case reports, the children didn’t spread the measles to anyone else.

So why are you waiting to know the genotype of the measles strain causing the outbreak in your area? Hopefully, it isn’t to help you decide whether or not to vaccinate and protect your kids. While it is interesting to know where the outbreak originated, you can bet that it isn’t a vaccine strain.

More on Vaccine Strains Causing Measles Outbreaks

Vaccine-Driven Resistance of Bacteria and Viruses

It is well known that bacteria and viruses can become resistant to antibiotic and anti-viral drugs.

From amoxicillin for Streptococcal pneumonia infections to amantadine for the flu, resistance is a growing problem that is limiting how easily we can treat many infections.

Vaccine-Driven Resistance of Bacteria and Viruses

Since bacteria and viruses seem to have such an easy time developing resistance against commonly used drugs, do we see the same thing with vaccines?

Fortunately, no.

We do not see bacteria or viruses creating resistance in our vaccines so that they no longer work.

For example, despite what you may hear, the MMR vaccine still prevents all wild strains of measles.

What about the pertussis vaccine and the fact that we are finding more and more strains of pertactin-negative pertussis bacteria? Doesn’t that mean that the Bordetella pertussis bacteria have mutated and are causing a pertussis resurgence because they are resistant to the vaccine?

While an interesting theory, pertactin is only one of the components (antigens) of the pertussis bacteria that are in pertussis vaccines that help them to induce immunity. Others can include filamentous hemagglutinin, chemically or genetically detoxified pertussis toxin, and fimbrial-2 and fimbrial-3 antigens.

So no, pertactin-negative pertussis bacteria are not driving outbreaks of pertussis or whooping cough, and they have not become resistant to pertussis vaccines.

Vaccine-Induced Pathogen Strain Replacement

What about the fact that we sometimes seen a rise in new bacteria once a vaccine wipes out the bacteria it works against?

While this type of vaccine-induced pathogen strain or serotype replacement can happen, it is not because the bacteria develop any kind of resistance. Some vaccines can only target specific strains of a virus or bacteria. The latest version of Prevnar, for example, can prevent the 13 strains of Streptococcal pneumonia that are most likely to cause disease in children. That leaves out over 75 other strains.

And the Hib vaccine only prevents Haemophilus influenzae type b infections. There are five other H. flu serotypes (a-f) and other non-typeable strains that aren’t covered by the Hib vaccine.

The same goes for the meningococcal vaccines. None of them cover all meningococcal serotypes.

Isn’t it just as bad if one of those other strains starts growing after your kids are vaccinated?

While it certainly sounds bad, as it seems like you are just replacing one bacteria for another, it really isn’t.

Rates of invasive pneumococcal disease have decreased dramatically since Prevnar was introduced.
Rates of invasive pneumococcal disease have decreased dramatically since Prevnar was introduced. Photo courtesy of the CDC.

Why not?

Because the replacement bacteria are often much less likely to cause invasive disease and the levels of disease they do cause don’t come anywhere close to pre-vaccine levels.

Vaccines work, even when something like vaccine-induced pathogen strain replacement happens.

Vaccines Can Help Prevent Drug Resistance

If you are really concerned about antibiotic resistance, you would want more people vaccinated.

Not only do vaccines not lead to an increase in vaccine or drug resistant bacteria or viruses, but they can help us fight the growing problem of drug resistance.

“Vaccinating humans and animals is a very effective way to stop them from getting infected and thereby preventing the need for antibiotics.”

WHO on Why is vaccination important for addressing antibiotic resistance?

Consider all of the people who take Tamiflu or antibiotics when they get the flu because they didn’t get a flu shot?

Or how many antibiotic prescriptions haven’t been written because kids did get vaccinated with Prevnar and never got an ear infection, pneumonia, or meningitis?

Vaccines in the pipeline could help even more.

What to Know About Vaccine-Driven Resistance

Vaccines are not causing an increase in vaccine-resistant bacteria or viruses and can actually help us fight the growing problem of antibiotic resistant bacteria.

More About Vaccine-Driven Resistance