thank you for the info and links Brainless - really appreciate you sharing your experiences. and its useful to know that your dogs avoiding water may be at least part of the reason you avoid the lepto vaccine.
and thank you too klb for sharing your experiences. that's interesting that you only start lepto vaccines a month after the DHP ones have been completed... which if you are vaccinating at 12 and then 16 weeks as you said earlier means you wouldn't be starting lepto vaccines until the dogs are around 20 weeks old, right? i believe the lepto protocol requires 2 lots of the lepto vaccines 2 weeks apart with onset of immunisation expected a week after the 2nd jab, in which case your dogs wouldn't be covered by the vaccine until they were 23 weeks old. do you make any kind of effort to avoid letting the dogs near water prior to 23 weeks? i can see on your profile that you breed GSPs; the puppy i am getting is a Vizsla, so i'm keen to hear any and all advice on gundogs!

the first information i got on vaccines was this link from the Kennel Club:
http://www.thekennelclub.org.uk/media/106031/vaccinationas.rtf. based on reading this i didn't understand that the vaccine for Leptospirosis was any different to the ones for Canine Distemper, Hepatitis & Parvovirus.
but now that i've learnt that Leptospirosis is very different to Canine Distemper, Hepatitis & Parvovirus i've done some more research. will pop below what i found in case it ends up being useful to anyone in the future reading this thread:
First off from the The World Small Animal Veterinary Association (WSAVA) (which is the resource my local vet said they go by):
http://www.wsava.org/sites/default/files/WSAVA_OwnerGuidelines_September2010.pdf * The MLV CDV and rCDV, as well as the MLV CPV-2 and CAV-2 vaccines can provide up to a lifetime of immunity when one or, preferably, two doses are given in the absence of MDA. For the core vaccines (CDV, CPV-2, CAV-2), the VGG recommends revaccination at 1 year of age or 1 year after the puppy series ends, then not more often than every 3 years. For rabies, revaccination should be at 1 year or less and then every 3 years or less, depending on local regulations. In contrast to the long (many years) DOI for the core vaccines, the optional (noncore) vaccines generally provide only 1 year or less DOI. Also, unlike the core vaccines that are often 99% effective when the animal is properly immunized,
many of the non-core vaccines have an efficacy of 70% or less.
* The non-core vaccines can be started before or after completion of the core vaccines.
Ideally the non-core vaccines would be given only when needed, starting two or more weeks after completion of the core viral vaccines. Many, but not all, non-core vaccines (e.g. those that protect from leptospirosis or borreliosis [Lyme disease]) require two doses administered 2 – 4 weeks apart because they are non- infectious (killed/inactivated) vaccines. In contrast to the core vaccines, which have a long DOI, most of the non-core vaccines must be given annually and sometimes more often for animals at very high risk of disease.
NB:
MLV = Modified Live Vaccine
CDV = Canine Distemper Virus
rCDV = recombinant Canine Distemper Vaccine
CPV-1 = Canine ParvoVirus type 1 (discovered in 1967 in Germany)
CPV-2 = Canine ParvoVirus type 2 (disease commonly associated with the parvovirus since its mutation from CPV-1 in the 1970s)
CAV-1 = Canine AdenoVirus type 1 (Infectious canine hepatitis caused by canine adenovirus type-1)
CAV-2 = Canine AdenoVirus type 2 (similar enough to CAV-1 that vaccine for one creates immunity for both. CAV-2 vaccine apparently less likely to cause side effects than CAV-1 vaccine)
MDA = Maternally Derived Antibodies
DOI = Duration Of Immunity
and some further research, although the quality of these references may or may not be questionable:
http://www.iwsca.org/Puppy%20Packet/Health%20Info/Vaccination/Vaccine%20101%20-%20R%20Schultz.doc * Non-core vaccinations include para-influenza, Bordetella bronchiseptica (kennel cough), Borrelia burgdorferi (Lyme), and leptospirosis. These vaccines should be administered only to dogs whose geographical location, local environment, or lifestyle places them at risk of contracting each of the specific infections.
* Interestingly, as opposed to the viral vaccines,
immunity from bordetella and lepto vaccines often lasts less than one year because they are bacterial diseases. And neither actually prevents the disease, but rather manages the disease and its severity. Lepto vaccines are the most reactogenic of all the vaccines, even more so than the rabies vaccines. * Coronavirus (CCV) and giardia vaccines are not recommended, as the 2006 AAHA Guidelines note, “Prevalence of clinical cases of confirmed CCV disease does not justify vaccination.”
* If vaccinating a puppy with non-core vaccines, in general, with the exception of intranasal bordetella, which can be given with the core vaccines, the viral vaccinations should be given first, and the bacterials should not be mixed.
http://www.abrl.org/files/vaccinesWDJ0808.pdf * repeats the from the link above...
* Vaccines themselves do not cause autoimmune disease, but in genetically predisposed animals they may trigger autoimmune responses followed by disease – as can any infection, drug, or a variety of other factors.
http://www.shalako.com/vaccine.htm * Multiple components in vaccines compete with each other for the immune system and result in lesser immunity for each individual disease as well as increasing the risk of a reaction. Canine Corona Virus is only a disease of puppies. It is rare, self limiting (dogs get well in 3 days without treatment). Cornell & TexaA&M have only diagnosed one case each in the last 7 years. Corona virus does not cause disease in adult dogs.
Leptospirosis vaccine is a common cause of adverse reactions in dogs. Most of the clinical cases of lepto reported in dogs in the US are caused by serovars (or types) grippotyphosa and bratsilvia. The vaccines contain different serovaars eanicola and ictohemorrhagica. Cross protection is not provided and protection is short lived.
Lepto vaccine is immuno-supressive to puppies less than 16 weeks.
http://www.lantanaatlantis.com/images/Checkup/VaccinationRecommendationsDogs.pdf * see table re risks and suggested vaccination schedule