Why It’s Important (if used):
FIV infection, once acquired, is lifelong. It can remain latent for years, but eventually many FIV-positive cats suffer from chronic infections (gum disease, respiratory infections, etc.), weight loss, and other signs of immune system failure. The vaccine was developed to help at-risk cats (outdoor cats in high-FIV areas) avoid contracting the virus. However, the FIV vaccine had limitations: it wasn’t 100% effective and only covered certain subtypes of the virus​. Additionally, vaccinated cats would test positive on FIV screening tests (because tests detect antibodies, which the vaccine induces)​, complicating diagnosis. Due to these issues and availability concerns, the vaccine is not widely used today. If you are in a country where an FIV vaccine is offered, it might be considered for cats at very high risk (like cats that roam and fight). For most pet cats, focusing on preventing fights and keeping cats indoors or neutered (to reduce aggression) is the primary way to avoid FIV. In summary, FIV vaccination is a topic to discuss with your vet only if your cat has a lifestyle that makes FIV likely.
What to Expect: (If the vaccine is administered) The FIV vaccine required a series of three initial doses given about 2–4 weeks apart, and then annual boosters to maintain immunity​. This is more intensive than most vaccines. The shot itself is similar to other cat vaccines under the skin. Cats generally tolerate it fine. However, because the vaccine can interfere with FIV blood tests, vets would ideally microchip any cat receiving it and keep documentation that the cat is vaccinated, so that in the future a positive FIV test could be interpreted correctly (knowing it could be from the vaccine, not true infection). This confusion – a vaccinated cat being indistinguishable from an infected cat on tests – is one reason many vets chose not to use this vaccine unless absolutely necessary. If given, you’d expect side effects similar to other vaccines: mild lethargy or soreness in some cats for a day or two.
Possible Side Effects or Risks: The FIV vaccine shared similar general risks to other vaccines: mainly minor, transient side effects. There wasn’t strong evidence of severe reactions at a higher rate than other cat vaccines. The biggest “risk” was the testing issue mentioned – a vaccinated cat would carry FIV antibodies and thus test positive on standard tests​. This could lead to potential misidentification of a cat as FIV-infected, which might have serious consequences (for example, in a shelter, a positive test might lead to isolation or even euthanasia if the history of vaccination isn’t known). For this reason, microchipping and clear record-keeping were essential. As with any injection, there was a minute risk of injection-site sarcoma (see FeLV section), but no evidence suggested the FIV shot was more likely to cause that than other vaccines. Now that it’s largely discontinued, today’s pet owners mostly won’t face FIV vaccine decisions. Instead, the focus is on managing behavior: keeping cats indoors or limiting their range, neutering to reduce fighting, and testing new cats before introductions.
When to Schedule It: If you live in an area of the world where FIV vaccination is offered and your vet recommends it, it would typically be started after 8 weeks of age for kittens at risk, with the 3-shot initial series (e.g., at 8, 12, and 16 weeks) and then boosted yearly. In practice, very few pet cats receive this vaccine now. Instead, testing for FIV is important: have your cats tested at least once, and re-test if they are ever exposed or if they have unknown status. If you adopt a new adult cat, do an FIV/FeLV blood test before mixing them with your existing cats. If your cat goes outdoors and could get into fights, schedule regular FIV tests (perhaps annually or if any fight wounds occur) so you know their status. Early detection won’t cure FIV, but it can prompt you to manage them differently (keeping them strictly indoors to prevent spread and monitoring health closely). Essentially, the “routine care” related to FIV nowadays is testing and prevention via behavior, rather than vaccination.
FAQs or Common Concerns:
- Q: My cat is FIV-positive. Is there a vaccine to help them or to protect my other cat?
A: There’s no vaccine that can help an already-infected cat – vaccines work by preventing infection. For your other FIV-negative cat, unfortunately the vaccine is no longer available in most places. The best course is to keep the FIV-positive and negative cats separated to avoid bites, or if they are friendly, they may cohabit with relatively low risk as long as they don’t fight (FIV isn’t spread by casual contact in the home in most cases). Always consult your vet about managing an FIV-positive cat in a multi-cat household. They might suggest careful introductions or maintaining separate living areas if there’s any chance of aggression. And of course, ensure the FIV-positive cat is neutered (if male) to reduce any territorial behavior. - Q: If the FIV vaccine isn’t used anymore, how do I protect my cat from FIV?
A: The key is lifestyle management. Keep your cat indoors, or only allow supervised outdoor time (e.g., on a leash or in an enclosed “catio”). If your cat does go outside, neutering/spaying will reduce roaming and fighting. Try to minimize encounters with unknown cats. Basically, prevent the kind of fighting that leads to deep bites​. If your cat is an outdoor scrapper by nature, you accept some risk – but you can use things like providing escape routes (so they don’t feel cornered into fighting) or timing their outings when other cats are less active. Community TNR (trap-neuter-return) programs also help by reducing the population of intact males that fight. In summary, avoidance of exposure is the primary “vaccine” against FIV today. - Q: I heard the FIV vaccine made cats test positive – how would I know if my cat has FIV or it’s the vaccine?
A: This was indeed the tricky part. There was a special test that could sometimes distinguish vaccine antibodies from infection, but it wasn’t widely available. The practical solution was: only cats with high exposure risk got vaccinated, and those cats were microchipped and had records indicating they’d been vaccinated. If your cat was vaccinated for FIV, any future vet or shelter would need to know that history to properly interpret an FIV test. Since the vaccine isn’t around now, it’s mostly a historical concern. If you adopt a cat and they test FIV-positive, one question to ask the former vet or shelter is if they were vaccinated for FIV in the past (some cats vaccinated years ago might still test positive). Distinguishing vaccine vs. true infection can be complex; your vet might send out specialized tests or simply treat the cat as FIV-positive to be safe. Again, this scenario is uncommon now due to the vaccine’s absence in the market.
Conclusion: The FIV vaccine is largely a thing of the past in most regions, due to issues with effectiveness and testing interference​. Protecting cats from FIV today relies on preventive habits: keeping cats indoors or in controlled environments, reducing fights (through neutering and monitoring interactions), and testing cats so you’re aware of their status. If you live where an FIV vaccine is available and your cat is in a high-risk category (e.g., an outdoor feral colony cat or barn cat), discuss the pros and cons with a veterinarian. For the average pet cat, the best defense is simply avoiding exposure. Fortunately, FIV spreads primarily through bites, so it’s not easily caught by cats who aren’t scrapping with others​. By being a responsible pet owner – preventing roaming and fighting – you can essentially do what the vaccine aimed to do. Should circumstances change (say you move somewhere with a lot of aggressive stray cats), revisit the topic with a vet to see if any new vaccine options exist. In summary, focus on routine testing and providing a safe environment; that’s the current standard of care regarding FIV.
