Tag: incubation period

Post-Exposure Prophylaxis With Vaccines Works

You know that vaccines can work to prevent you from getting an infection (pre-exposure prophylaxis), but did you know that some vaccines work even after you have been exposed to a disease?

Post-Exposure Prophylaxis With Vaccines Works

That’s right, some vaccines work as post-exposure prophylaxis too!

Post-exposure prophylaxis can help prevent tetanus infections. Photo by Petrus Rudolf de Jong (CC BY 3.0)
Post-exposure prophylaxis can help prevent tetanus infections. Photo by Petrus Rudolf de Jong (CC BY 3.0)

It’s especially helpful for those diseases that have a long incubation period.

“People exposed to measles who cannot readily show that they have evidence of immunity against measles should be offered post-exposure prophylaxis (PEP) or be excluded from the setting (school, hospital, childcare). To potentially provide protection or modify the clinical course of disease among susceptible persons, either administer MMR vaccine within 72 hours of initial measles exposure, or immunoglobulin (IG) within six days of exposure.”

CDC on Measles for Healthcare Professionals

In addition to measles, post-exposure prophylaxis can work for hepatitis A, hepatitis B, rabies, and tetanus.

With hepatitis B, rabies, and tetanus, after exposure, you would typically also get a dose of immunoglobulin, in addition to a hepatitis B, rabies, or tetanus vaccines (DTaP or Tdap). With hepatitis A, immunoglobulin is typically only given if you are at high risk for a severe infection.

Why not just get immunoglobulin, which is basically a big shot of antibodies?

“Human rabies immune globulin (HRIG) is administered only once, at the beginning of anti-rabies prophylaxis, to previously unvaccinated persons. This will provide immediate antibodies until the body can respond to the vaccine by actively producing antibodies of its own.”

CDC on Human Rabies Immune Globulin

It’s because the passive protection that you get from the antibodies in the immunoglobulin will quickly wear off, often sooner than your body clears the virus that you were exposed to.

Getting a vaccine at the same time helps make sure that you are making your own antibodies to keep you protected when that happens.

Unfortunately, post-exposure prophylaxis with a vaccine doesn’t work for most other vaccine preventable diseases. Those who are unvaccinated and high risk can get protection against chickenpox (VariZIG) though.

Want to make sure you are protected? Get vaccinated well before you are ever exposed to measles, chickenpox, hepatitis A or B, and other vaccine preventable diseases.

More on Post-Exposure Prophylaxis

How Many Active Cases Are There in Rockland County?

Three new cases were just reported in the Rockland County measles outbreak, pushing the total count to 161 cases in an outbreak that has been going on since September of 2018.

These are record breaking numbers.

Misleading? Fear mongering? Isn't that ironic???
Misleading? Fear mongering? Isn’t that ironic???

So of course, it’s time to move the goalposts!

How Many Active Cases Are There in Rockland County?

The number of active cases in an outbreak is an important number.

It’s a sign that the outbreak is under poor control.

For example, there were 45 new cases of measles in Brooklyn this week, following reports of 33 new cases the previous week. In fact, in the past 21 days, the case count in Brooklyn went from 158 to 259, which likely means that there have been over 100 active measles cases in Brooklyn during that time.

What about Rockland County?

In the past three weeks, the case count in Rockland County has increased by 16.

Why is three weeks an important number?

Because that’s how long it takes to develop symptoms after they have been exposed to someone with measles.

The problem in Rockland County, as Ed Day said in his press conference, is that people hadn’t been cooperating with the health department. So it is hard to actually know how many active cases there are. Is it five cases, as someone at the health department recently told an anti-vaccine women impersonating a caller who was concerned about her infant?

If so, that’s five cases too many!

The most important thing to understand, is that as we continue to see new cases, there is no sign that the outbreaks are stopping.

And the only numbers that really matter are ZERO new cases for 42 days.

That’s when the outbreaks will be declared over.

Let’s hope that we get there before we are talking about a new number, someone dying with measles.

More on Active Cases in Rockland County


What Is a Vaccine?

You know what a vaccine is, right?

The word vaccine comes from the vaccinia virus that was in the original smallpox vaccine.
The word vaccine comes from the vaccinia virus that was in the original smallpox vaccine.

The flu shot you get each year is a vaccine.

Vaccine: A product that stimulates a person’s immune system to produce immunity to a specific disease, protecting the person from that disease. Vaccines are usually administered through needle injections, but can also be administered by mouth or sprayed into the nose.

Immunization: The Basics

The smallpox shot that Edward Jenner developed was a vaccine.

Vaccine Definitions

While that is an easy enough definition to understand, that there are many different types of vaccines does make it a little more complicated.

There are:

  • Live-attenuated vaccines – made from a weakened or attenuated form of a virus or bacteria
  • Inactivated vaccines – made from a killed form of virus or bacteria
  • Subunit, recombinant, polysaccharide, and conjugate vaccines – made from only specific pieces of a virus or bacteria
  • Toxoid vaccines – made to target a toxin that a bacteria makes and not the bacteria itself

And of course all of these types of vaccines work to produce immunity to specific diseases – vaccination.

Immunization: A process by which a person becomes protected against a disease through vaccination. This term is often used interchangeably with vaccination or inoculation.

Immunization: The Basics

What other definitions are important to know when you talk about vaccines?

  • active immunity – immunity that you get from having a disease (natural immunity) or getting a vaccine and making antibodies
  • adjuvant – a substance that helps boost your body’s immune response to a vaccine so that you can use a minimum amount of antigen, reducing side effects
  • antibodies – protective proteins that you make against antigens
  • antigens – specific substances (can be part of a virus or bacteria) that trigger an immune response
  • attenuation – a virus or bacteria that is made less potent, so that it can produce an immune response without causing disease
  • elimination – getting rid of a disease in a specific area
  • endemic – the baseline level of disease in an area
  • eradication – getting rid of a disease everywhere (smallpox)
  • epidemic – an increase in the number of cases of a disease over a large geographic area
  • herd immunity – when enough people in a community are protected and have immunity, so that disease is unlikely to spread
  • immunity – protection against a disease
  • incubation period – how long it takes to develop symptoms after you are exposed to a disease
  • outbreak – an increase in the number of cases of a disease over a small geographic area
  • pandemic – an increase in the number of cases of a disease over several countries or continents
  • passive immunity – temporary immunity that you get after being given antibodies, either via a shot of immunoglobulin or a mother’s antibodies are transferred to her baby through her placenta
  • placebo – classically defined as “a comparator in a vaccine trial that does not include the antigen under study”
  • quarantine – isolating someone so that they don’t get others sick
  • titer – an antibody count that can often be used to predict immunity

Got all of that?

So what about variolation, the process that was used before Jenner developed his smallpox vaccine? Was that also a vaccine?

It did produce immunity to smallpox, which is the basic definition of a vaccine, but still, variolation is typically concerned an immunization technique and not a vaccine.

More on Vaccine Definitions

How Contagious Is Measles?

Did you hear about the folks in New York who got quarantined isolated on the Emirates plane from Dubai?

Turns out that about 10 passengers had the flu or other cold viruses.
Although the worry was likely about MERS, it turns out that about 19 passengers had the flu or other cold viruses.

News like that and folks getting exposed to other infectious diseases, probably has them wondering just how contagious these diseases are. Do you have to be sitting next to someone to get them? In the same row? On the same floor?

Understanding Your Risk of Catching a Disease

Fortunately, most diseases are not terribly contagious.

We worry about some things, like SARS and Ebola, because they are so deadly, not because they are so contagious or infectious.

Wait, contagious or infectious? Aren’t they the same thing?

To confuse matters, some infectious diseases aren’t contagious, like Lyme disease. And some vaccine-preventable diseases are neither infectious nor communicable. Think tetanus. You may have never thought of it that way, but you aren’t going to catch tetanus from another person. Of course, that’s not a good reason to skip getting a tetanus shot!

To understand your risk of getting sick, you want to understand a few terms, including:

  • infectious disease – a disease that can be transferred to a new host
  • communicable – an infectious disease that can be transferred from one host to another
  • non-communicable – a non-infectious disease which can not be transferred from one host to another
  • contagiousness – an infectious disease that is easily transferred from one person to another
  • infectivity – the ability of an infectious agent to cause an infection, measured as the proportion of persons exposed to an infectious agent who become infected. Although this doesn’t sound much different from contagiousness, it is. The Francisella tularensis bacteria is highly infectious, for example, to the point that folks exposed to a culture plate are given antibiotics or put on a fever watch. Few of us get tularemia though, because transmission is through tick bites, hunting or skinning infected rabbits, muskrats, prairie dogs and other rodents, or inhaling dust or aerosols contaminated with F. tularensis bacteria. So if you get exposed, you will probably get sick, but there is a low probability for getting exposed.
  • incubation period – the time it takes to start having symptoms after you are exposed to an infectious disease. A longer incubation period increases the chances that someone will get exposed to a disease and travel home before getting sick. A shorter incubation period, like for influenza, means that a lot of people can get sick in a short amount of time.
  • contagious period- the time during which you can spread the illness to other people and may start before you have any symptoms
  • quarantine – used to separate people who have been exposed to a contagious disease and may become sick, but aren’t sick yet
  • isolation – used to separate people who are already sick with a contagious disease
  • transmission – how the disease spreads, including direct (direct contact or droplet spread) vs indirect transmission (airborne, vehicleborne, or vectorborne)
  • R0 (r nought) – the basic reproductive number or the number of new infections originating from a single infectious person among a total susceptible population
  • Rn – the net reproductive number, which takes into account the number of susceptibles in a community
  • infectious period – how long you are contagious

Got all that?

How Contagious Is Measles?

If not, understanding how easily you can get measles should help you understand all of these terms.

Measles is highly contagious, which is likely why all of the Brady kids got sick.
Measles is highly contagious, which is likely why all of the Brady kids got sick.

Measles is highly contagious, with a very high R0 number of 12 to 18.

That’s because:

  • the measles virus can live for up to two hours on surfaces and in the airspace where an infected person coughed or sneezed
  • infected people are contagious for up to four days before they have a rash and even know that they have measles, so expose lots of people even if they get put in isolation once they get diagnosed
  • infected people continue to be contagious for up to four days after the rash appears, so can continue to expose people if they aren’t put in isolation

So you don’t need to have someone with measles coughing in your face to get sick. If they coughed or sneezed at the grocery store, on the bus, or at your doctor’s office and then you entered the same area within two hours, then you could be exposed to the measles virus and could get sick.

Why don’t we see at least 12 to 18 people in each measles outbreak anymore?

That’s easy. The definition for R0 is for a total susceptible population. Most folks are vaccinated and protected, so even if they are around someone with measles, they typically won’t get sick.

Still, up to 90% of folks who aren’t immune and are exposed to measles will catch it. That includes infants too young to be vaccinated, kids too young to be fully vaccinated, and anyone who has a true medical exemption to getting vaccinated.

The measles has a very high R0 is easier to see when you compare it to those of some other diseases

 

Infection R0
Diphtheria 6-7
Ebola 1.5-2.5
Flu 1.4-4
MERS 2-8
Mumps 4.7
Pertussis 5-17
Polio 2-20
RSV 3
SARS 2-5
Smallpox 5-7
Varicella 8-10

Why such a big range for some diseases?

These are estimates and you are more or less contagious at different stages of each illness.

Fortunately, in most cases you can just get vaccinated and protected and don’t have to worry too much about them.

More on the Contagious Periods of Diseases