Three injections, 3 to 4 weeks apart, with the last one on or after 16 weeks of age. That is the whole core plan for a kitten, and nearly every failure is a timing failure rather than a product failure. A series that stops at 12 weeks leaves a 4-week window where maternal antibody is gone and the kitten is not yet covered.
Why 3 doses and not 1
A kitten is born with antibody absorbed from colostrum in the first 16 to 24 hours of life. That antibody blocks a vaccine exactly as well as it blocks infection, and it fades at a different rate in every kitten: some are clear by 8 weeks, some still carry it at 16. A single injection therefore cannot be trusted. In a kitten still carrying antibody it does nothing, and routine litters are not titre-tested to find out which kitten that is.
The fix is arithmetic. Give 1 dose at 6 to 8 weeks to start some immunity, repeat every 3 to 4 weeks, and make sure at least 1 dose lands after the maternal antibody has fallen. Three doses at 8, 12 and 16 weeks covers the whole fade window. A kitten that starts at 6 weeks needs a 4th dose at 18 to 19 weeks for the same reason, not because 4 is better than 3.
The week-by-week map
| Age (weeks) | Core dose | Injections that visit | Typical weight (kg) | Also at that visit |
|---|---|---|---|---|
| 6 to 7 | 1 | 1 | 0.7 | First weight, first deworming round |
| 8 to 9 | 2 if already started at 6 weeks, otherwise 1 | 1 | 0.9 | Microchip, flea plan, stool check |
| 10 to 12 | 2 | 1 | 1.2 | Deworming round, first nail trim |
| 14 to 15 | None | 0 | 1.5 | Weight trend, teeth, book the 16-week date |
| 16 | 3 | 1 | 1.8 | The line: count doses from here |
| 18 to 19 | 4 | 1 | 2.1 | Only if dose 1 was given at 6 weeks |
Read the age column as the only fixed point. Doses 1 and 2 are flexible by a week or so; the dose that must land at or after 16 weeks is not. When a clinic compresses the early part of the schedule for convenience, the 16-week visit still has to happen.
The 16-week line, and the 4-dose case
16 weeks sits past the upper end of the maternal antibody window, which is why the final dose belongs there rather than at 12. Two injections at 8 and 12 weeks with nothing after is the most common gap seen in first-year kittens: 2 visits, 1 owner convinced the cat is finished, and a 5-month-old with partial cover going into a house with an older cat.
Rabies runs on its own clock: 1 dose at 12 to 16 weeks in most places, a second at 12 months, then every 1 to 3 years according to local law and the product used. Feline leukaemia virus is a separate decision rather than an automatic add-on: 2 doses 3 to 4 weeks apart starting at 8 to 9 weeks, aimed at kittens that will go outdoors or share a house with a known positive cat.
What else happens at each visit
The injection is 1 minute of a 20-minute appointment. The rest is the part that catches problems: weight on the same scale each time, with a gain of 60 to 100 g a week expected to 16 weeks; a body condition check; a look at the teeth, the umbilicus and the coat; a stool check for parasites; and a deworming round every 2 weeks from 2 to 12 weeks, then monthly to 6 months.
The home frequency list for the same 14 weeks runs in parallel: weigh weekly to 16 weeks, trim nails every 2 weeks, scoop the litter box twice a day, wash the box weekly, and weigh the food, so that a 300 g kitten eating 60 to 80 g of wet food a day is a measured number rather than a guess. Food volume follows the weaning schedule once the kitten is off the bottle, and play has its own clock at the play schedule: 2 or 3 sessions of 10 minutes, because a kitten that plays hard at 21:00 is awake at 02:00.
3 schedule mistakes that look like bad luck
Starting at 10 to 12 weeks. The kitten then needs 2 doses 3 to 4 weeks apart, and the second lands at 15 to 16 weeks at best, so the series ends with 2 injections and no margin. Counting a 15-week dose as the 16-week dose. Seven days short is still short: the maternal antibody window runs to 16 weeks, which is why that date is the one to protect. Splitting the series across 2 clinics. Two cards, 2 record systems, and a booster date nobody can reconstruct at 12 months. One kitten, 1 card, 1 written schedule.
The 48 hours after a dose
Stay 15 to 30 minutes in the waiting room after the first injection. Expect mild sleepiness and a slightly flat appetite for 24 to 48 hours, and a small firm lump under the skin that fades inside 3 weeks is common. Call the clinic the same day for facial swelling, vomiting more than 2 times, hives, or any difficulty breathing, and give no human antihistamine while you wait for the callback.
Boosters after 12 months
At 12 months the kitten gets 1 booster, then the core interval stretches to every 3 years in most protocols, with rabies following local law. A titre test can substitute for the core booster in some households: it measures circulating antibody, and most veterinarians accept a positive result for the viral core components. It does not replace the rabies certificate, which is a legal document rather than an immunity question. If the breed is still a guess, the breed quiz takes 2 minutes and sets the adult weight you plan the 12-month booster around. The annual visit still happens; the injection is 1 item on a 6-item list that also covers weight, teeth, heart and lungs, a parasite plan and a behaviour question, which is why the exam is worth keeping in a year with no shot.
5 steps to book now
- Put the 3 target dates — 8, 12 and 16 weeks — on the calendar today and treat the 16-week one as fixed.
- Weigh the kitten weekly on a kitchen scale and write it down; a flat week at 10 weeks is a reason to call.
- Ask for the deworming dates in writing, because the every-2-weeks rhythm runs to 12 weeks.
- Decide rabies at the 12-week visit so the 16-week appointment stays a 1-injection visit.
- Keep a photo of the vaccination card on your phone; boarding, travel and insurance all ask for dates.
Frequently asked
Can my kitten go outside after 2 injections?
Not safely. Two doses at 8 and 12 weeks leave the window from 12 to 16 weeks partly open, and that is exactly when maternal antibody has fallen but the series is not finished. Most veterinarians ask for the final dose at 16 weeks plus 7 to 10 days before a kitten meets unknown cats or walks on shared ground.
What if we miss the 12-week appointment by a month?
Restart the count rather than skip ahead: 2 doses still 3 to 4 weeks apart, with the last one at or after 16 weeks. A single late dose does not repair a gap, because the point of the series is repeated exposure across the whole maternal antibody fade window, not one well-timed injection.
Do indoor-only kittens need the full series?
Yes for the core vaccine. Panleukopenia virus survives in a household for months on shoes, hands and carrier bags, so an indoor kitten is exposed without ever stepping outside. Rabies and feline leukaemia are the 2 decisions that legitimately change for an indoor cat, and local law governs rabies.