VACCINATION is generally agreed
to be one of those bread-and-butter
treatments that make an important
contribution to practice profitability.
That model has been challenged in
recent years as the whole issue of
timing of vaccination and re-
vaccination intervals has become more
contentious. This is a field where
opinion and practice are changing
rapidly and clinicians may want to
consider reviewing long-established
protocols.
Basic principles
Vaccination relies on
using inactivated
(killed) viruses or
bacteria and modified
attenuated (live)
viruses or bacteria to
prompt the immune
system to produce
antibodies. More
recently, live vectored
vaccines or subunit
vaccines have also
become a reality.
Adjuvants are used to
enhance the immune response to
vaccine antigens.
Polyvalent canine vaccines have
increasingly become the norm in
veterinary practice, allowing dogs to be
vaccinated against several diseases with
one injection, sometimes with very little
rationale if naturally acquired disease
produces mild clinical signs.
With research striving forwards,
vaccines have now been developed to
immunise against an increasing number
of diseases. This has led to some
experts taking the view that vaccines
should be split into “core” and “non-
core” categories, administered on a risk
assessment basis, using up to date
information on factors such as the
disease risk and the duration of
immunity.
Another concern is that an
increased antigenic load may predispose
animals to immune-mediated disease. It
was reported at the NAVC in 2006 that
the results of studies suggesting a cause
and effect relationship are conflicting
but that several studies have
demonstrated a short period of
immunosuppression can occur post
vaccination using polyvalent vaccines;
an effect that is not thought to be
significant in the healthy dog1.
The UK Practice Overview of
Canine Health (POOCH) study carried out in 2006 found no evidence that the
three-month period post vaccination
was associated with ill health and
vaccines tend to have a very good
safety profile2.
Guidelines and protocols
A number of guidelines have been
produced in recent years including the
American Animal Hospital Association
guidelines which were updated in 2006 and the WSAVA
vaccination guidelines
of 2007.3,4
The BVA also
produces a “frequently
asked questions”
document on its
website which states,
“Vets must use
vaccines in accordance
with the licence
stipulations … it would
be negligent of a vet
to deviate from the
medicinal information
available to them
and/or use a vaccine
not in accordance with … the summary of the
product characteristics or the datasheet.”5
In contrast, the AAHA guidelines in the US take the opinion that all
vaccines against distemper, parvovirus
and canine adenovirus-2 made by major
pharmaceutical companies “all produce
excellent immune responses and can be
soundly and reliably administered at the
discretion of the clinician in extended
duration of immunity protocols”.4
If data sheets are compared over
the last five years, many companies
have more recently included
information regarding extended
duration of immunity. Some still
recommend annual re-vaccination but
will also state that serological data
suggest that most dogs experience
extended immunity.
There needs to be some care in
how this is interpreted, as Paul Burr,
CEO of Biobest Laboratories, points
out, “Strong serological evidence of
immunity is an excellent marker of
protection. There is a view from some
respected individuals that once you
have shown a high positive antibody
titre the dog or cat is protected for life.
It is difficult to use evidence from field
studies to prove length of immunity
because of the chances of natural
exposure boosting immunity. Animals
with high titres are immune, but this
may or may not be due to vaccination
alone.”
All of this means that the onus of
decision making is on the clinician and
it is perhaps not surprising that many
are entering into a dialogue with vaccine manufactures to help formulate their
practice protocols.
Callum Blair, product manager at
Virbac, recommends that practices
formulate their protocol based on the
disease risk in the area, then take into
account individual circumstances. “We
have been helping many practices
develop their protocols and we
encourage clinicians to embrace
extended DOI routines where
appropriate.
“As part of that review process we
also show how annual health checks
can be embedded into those protocols
and demonstrate where the
opportunities for growth lie that will
promote long-term sustainability of the
practice business model.”
There are many instances where
practices will have to adapt their
protocols. Callum cites recent cases
where localised flooding resulted in
increased cases of leptospirosis – yet
the vaccine is considered in some
guidelines to be “non-core”, despite the
fact that in the UK there are zoonotic
implications and duration of immunity
is unlikely to extend beyond one year.
Timing of vaccination
The timing of puppy vaccinations is
another contentious area – with the
pressures for early socialisation on one
side and concerns to isolate vulnerable
puppies from infection on the other.
After suckling, a pup’s antibody titre will average
around 60-70% of that
of the dam.6,7
As maternally derived
antibody declines,
puppies become
vulnerable to infection
but if antibody levels stay
high for an extended
period, inoculated virus
does not replicate and
does not provoke
antibody production; this
may occur even when
maternal antibody is
insufficient to protect
against naturally derived infection.
Modified live vaccines are
recommended for effective protection
against distemper and parvovirus.8
Multiple primary vaccinations aim
to identify the point at which maternal
antibody is low enough to result in
successful immunisation and it is
important to note that AAHA and
WSAVA vaccine guidelines advise that
three vaccinations are given in total,
with a final dose given at 14-16 weeks,
contrary to the two-dose regime
recommended in most data sheets in
the UK.
There is widespread agreement that
the booster at one year of age is especially important to pick up the non-
responders from the primary
vaccination course and, anecdotally,
most cases of parvovirus “vaccine
breakdowns” tend to occur in the 9-15
month age group.
The 10-week finish for vaccination
protocols presents another dilemma for
clinicians. Mark Riggs of Merial says
the company remains firm in the belief
of a 12-week finish. “The levels of
maternally derived antibodies (MDA) at
12 weeks will be considerably lower
than at 10 weeks. As even small
amounts of MDA can interfere with
vaccine efficacy, it makes
immunological sense to wait until 12
weeks to finish vaccine courses. Many
independent vaccine guidelines go a
stage further than this and actually
recommend a third vaccine at 16 weeks
for the exact same reason.”
Various SPCs (the summary of
product characteristics document
produced by manufacturers for
licensing purposes) state 10 week
finishes are possible but clinicians must
bear in mind that 10 week finishes
should be considered the earliest time
to finish primary vaccine courses. For
clinicians who wish to examine the SPC
for individual products in detail, they
are posted on the VMD website.
Choosing a vaccine protocol
Where does all of this leave the
clinician? There are many factors that need to be
taken into account when
selecting a protocol –
those in affluent areas
with little evidence of
active parvovirus
infections may opt for a
three-year parvo
“booster” but it has been
suggested that clinicians
may also want to consider
the effects on “herd
immunity”: once the level
of immunity drops in the
general population, a few
cases can quickly trigger an epidemic – as the human population
has found to its cost recently as cases of
measles escalated.
Paul Burr sounds a note of caution:
“All animals are individuals and
extrapolating 90% of animals are
immune to an assumption that a
particular animal is immune is foolish.
It is dangerous to apply population
medicine statistics to individual private
patients. The owners care about
protection of their pet, not herd
immunity which does not really exist
for dogs and cats in Europe as
vaccination is too patchy.”
There are other important concerns
regarding vaccine compatibility. In some cases there are specific
instructions on the data sheet with
regard to completing a primary course
of vaccination using different brands; in
others the data may be absent because
positive evidence is not available.
Practices would be well advised to
consider their policy in this area and
consider issues such as informed
consent backed up using signed
disclaimers where the client declines to
follow the clinician’s recommendation.
This is true of any off-label use where
the clinician is departing from the data
sheet.
The Veterinary Defence Society
(VDS) recommends that clinicians keep
a record of all discussions around the
issue of informed consent and off-label
consent forms are available to VDS
members.
Vaccination is becoming an
increasingly complex issue and one of
the key criteria by which new puppy
owners and potential life-long clients
will judge your practice. It is important
then that vaccination policies can be
clearly communicated by the whole
practice team and that the highest
standards are applied in formulating protocols and adapting them to suit
individual needs.
References
1. Newest Vaccination Strategies for
Sporting Dogs, Fortney, W., NAVC
Congress 2006.
2. Edwards, D. S., Henley, W. E., Ely, E. R.
and Wood, J. L. N. (2006) Practice
Overview of Canine Health (POOCH).
3. WSAVA Guidelines for the vaccination of
Dogs and Cats:
www.wsava.org/PDF/Misc/
VGG_09_2007.pdf.
4. 2006 AAHA Guidelines Canine Vaccine
Guidelines, Revised.
www.aahanet.org/PublicDocument…
VaccineGuidelines06Revised.pdf.
5. BVA Vaccination – the Facts, available on
the BVA website.
6. Waner, T. (2002) Response of Puppies to
Vaccination with Canine Distemper and
Canine Parvovirus, WSAVA.
7. Coyne, M. (2202) Efficacy of Two Canine
Parvovirus Vaccines for Inducing
Seroconversion in Rottweiler and
Dobermann Pinscher Pups with Various
Levels of Maternally Derived Antibodies.
Veterinary Therapeutics I (1).
8. Ford, R. (2002) Canine Vaccination
Protocols. WSAVA.
