Deworming and vaccination: FMD protection drops to 6.25%
Deworming and vaccination scheduled on the same day cut foot-and-mouth disease protection to 6.25 percent in sheep. Giving the FMD vaccine alone reached 37.50 percent. A second vaccine in the same session was worse still, dropping protection to zero by day 28. The antigen load is not the problem. Immune competition is.
Why deworming and vaccination timing became a real problem
Foot-and-mouth disease virus is a highly contagious pathogen of cloven-hoofed livestock, and vaccination is the most economical control measure available. The practical constraint on intensive sheep farms is labor. Catching and handling animals stresses the flock and costs the farm money, so producers fold interventions into one session: the FMD vaccine, the clostridial vaccine, and the dewormer, all on the same day.
That routine makes operational sense and immunological nonsense. Nobody had tested under controlled conditions whether the combination damages the FMD response, which is the gap this trial filled. Field questions that come up constantly include the right ivermectin dose in sheep, whether anthelmintic and vaccine products can share a day, what a realistic fmd protection rate looks like, how to read an antibody titer sheep-side after a course, and where a deworming schedule and a sheep vaccination program should sit relative to each other.
How the trial was set up
Ninety-six healthy sheep from a commercial farm were enrolled after quarantine inspection. All were two months old, half male and half female, with a mean body weight of 18.0 plus or minus 3.5 kilograms. Every animal tested negative for FMDV serotype O antibodies (below 1:8) and negative for parasite ova on fecal examination before enrollment, so none entered the trial with existing immunity or a worm burden. Feed contained no antimicrobials or anthelmintics for the duration.
| Design element | Specification |
|---|---|
| Animals | 96 healthy sheep, 2 months old, half male half female |
| Body weight | Mean 18.0 plus or minus 3.5 kg |
| Pre-trial screening | FMDV serotype O negative (below 1:8), no parasite ova |
| Groups | 3 groups of 32 |
| Group A | FMD vaccine alone |
| Group B | FMD vaccine plus quadrivalent clostridial vaccine, same day |
| Group C | FMD vaccine plus ivermectin, same day |
| FMD vaccine | Bivalent inactivated, serotypes O and A, 1 mL intramuscular |
| Clostridial vaccine | Quadrivalent inactivated, 2 mL intramuscular |
| Ivermectin | 0.2 mg/kg subcutaneous, manufacturer’s recommended dose |
| Sampling | Days 7, 14, 21, and 28 after immunization |
| Assay | Liquid-phase blocking ELISA, serotype O specific |
| Protective threshold | Antibody titer at or above 1:128 |
| Statistics | Titres log2-transformed, one-way ANOVA per timepoint, p below 0.05 |
Antibody titer was defined as the reciprocal of the highest dilution producing an optical density above the 50 percent blocking threshold. The 1:128 cut-off follows the national standard for FMD vaccine efficacy evaluation, and animals reaching it were counted as immune-qualified.
Protection rates by group
The headline is uncomfortable for anyone who has combined these injections to save a handling day.
| Timepoint | Group A: FMD alone | Group B: plus clostridial | Group C: plus ivermectin |
|---|---|---|---|
| Day 7 | 53.13 percent (17 of 32) | 34.38 percent (11 of 32) | 25.00 percent (8 of 32) |
| Day 14 | 28.13 percent (9 of 32) | 28.13 percent (9 of 32) | 9.38 percent (3 of 32) |
| Day 21 | 34.38 percent (11 of 32) | 34.38 percent (11 of 32) | 25.00 percent (8 of 32) |
| Day 28 | 37.50 percent (12 of 32) | 0 percent (0 of 32) | 6.25 percent (2 of 32) |
Both co-administration groups showed significantly lower titers at every sampling point, and the ivermectin group was suppressed more than the clostridial group. By day 28 the clostridial group had no protected animals at all.
Two counter-intuitive findings
The first is that a vaccine given alone did not perform well either. Group A peaked at 53.13 percent protected on day 7 and was down to 37.50 percent by day 28. Fewer than four in ten sheep reached the protective threshold three weeks after a complete primary course. That is the baseline the trial measures against, and it sits lower than most producers would guess from a vaccine datasheet.
The second is that the mechanism of harm is not the needle or the injection site. Two vaccines, and one vaccine plus an anthelmintic, both suppressed the response. The common factor is immune competition.
The quadrivalent clostridial vaccine stimulates antibodies against several Clostridium toxin types. Give it on the same day as an FMD vaccine and the antigens compete for immune cells, cytokines, and response pathways. The FMD vaccine is inactivated and weakly antigenic, and it starts its response slowly, so it loses that contest. Activation, proliferation, and differentiation of specific B cells are inhibited and antibody secretion falls. Multi-component vaccines can also disturb the immune microenvironment and push immune-related cytokine expression down.
The contribution from ivermectin is separate and additive. Beyond killing worms it modulates innate and adaptive immunity, affecting dendritic cell maturation, T lymphocyte activation, and cytokine balance. Reported effects include inhibited lymphocyte proliferation, reduced macrophage phagocytic and processing function, and selective suppression of Th1 cytokine production. Put ivermectin and vaccine injections in the same session and the FMD response takes two hits.
What this means for deworming and vaccination scheduling
The trial design matters as much as the result. Animals were confirmed seronegative at entry and ovum-free, so the suppression shown here is not a pre-existing infection muddying the picture. The ivermectin dose was the label dose. The two interventions went in on the same day, which makes this a scheduling question rather than a product question.
Note what the study does not say. It does not test a separated schedule, so it cannot name the interval that restores protection. It does establish that same-day administration is the wrong default, and that one extra handling day costs less than a failed vaccination round.
Practical recommendations
- Do not co-administer the FMD vaccine with an anthelmintic on the same day. Protection fell to 6.25 percent at day 28 in this trial.
- Do not stack two vaccines in one session either. The clostridial combination produced zero protected animals at day 28.
- Treat anthelmintic timing as part of the vaccine protocol. Separate dates on the calendar keep sheep deworming and vaccination from colliding.
- Budget one extra handling day rather than accepting a compromised primary course.
- Re-check protection late, not early. Group A looked best on day 7 and declined after that, so a single early sample flatters the result.
- Confirm seronegative status before vaccinating naive stock. The trial screened every animal at entry, and field programs rarely do.
- Expect the FMD component to lose a co-administration contest. Inactivated and weakly antigenic is a poor starting position against a multivalent product.
Limitations
The trial ran for 28 days, so it captures the early immune response rather than full herd immunity at the end of a campaign. Group sizes were 32 per arm, adequate for the differences observed but leaving the exact magnitude of suppression imprecise. No power calculation preceded the experiment, and the sheep were two months old, so the findings speak most directly to young stock receiving a primary course. Antibody titer is a surrogate for protection, and reaching 1:128 follows a national efficacy standard rather than guaranteeing that an animal resists challenge. The mechanism proposed for the suppression draws on the wider literature instead of being demonstrated within this cohort. Only serotype O antibodies were measured even though the vaccine was bivalent, so the serotype A response under co-administration stays uncharacterized. Two limits are worth stating plainly. The fmd vaccine sheep received in this trial was a single commercial product, so vaccine immune interference may differ with other formulations, and vaccine co-administration practice varies widely across farms, which makes livestock vaccination timing a local decision rather than a fixed rule.
Bottom line
Same-day deworming and vaccination is a false economy. In this trial, adding ivermectin to an FMD vaccination session cut protection from 37.50 percent to 6.25 percent by day 28, and adding a second vaccine cut it to zero. The suppression runs through immune competition rather than through the products themselves, which leaves separation in time as the lever a farm actually controls. Schedule the anthelmintic on a different day, keep the FMD vaccine in a session of its own, and verify protection later in the course instead of at the first sampling point.
FAQ
Can you deworm and vaccinate sheep on the same day?
Not if the vaccine is against foot-and-mouth disease. In this trial, sheep given ivermectin and the FMD vaccine on the same day had a protection rate of 6.25 percent at day 28, against 37.50 percent for sheep given the vaccine alone. The suppression appeared at every sampling point from day 7 onwards, not only at the end.
Does giving two vaccines at once reduce immunity in sheep?
Yes, and in this trial the effect was severe. Sheep given a quadrivalent clostridial vaccine alongside the FMD vaccine had a protection rate of zero at day 28, down from 37.50 percent in the vaccine-only group. Titres were significantly lower at all four sampling points. Antigen competition for immune cells, cytokines, and response pathways is the proposed mechanism.
Why does ivermectin suppress the FMD vaccine response?
Because ivermectin does more than kill worms. It modulates innate and adaptive immunity, influencing dendritic cell maturation, T lymphocyte activation, and cytokine balance. Reported effects include inhibited lymphocyte proliferation, reduced macrophage phagocytic function, and selective suppression of Th1 cytokine production. Given with an inactivated vaccine, those effects fight the response the vaccine needs.
How long should you wait between deworming and vaccination?
This study does not establish a safe interval, because it only tested same-day administration. It establishes that same-day dosing is the wrong default and that the two procedures should be separated. Because no tested interval appears in the data, the practical step is to schedule the anthelmintic on a different day and re-check titers after the course rather than assume the separation worked.
Why is the FMD vaccine so vulnerable to interference?
Because it is inactivated and weakly antigenic, and it initiates immunity slowly. When antigens from a multivalent product compete for the same immune resources, the FMD component loses that contest. Activation, proliferation, and differentiation of specific B cells are inhibited, antibody secretion falls, and titers drop. Multi-component products can also down-regulate immune-related cytokines.
What protection rate does the FMD vaccine give on its own?
Modest, in this cohort. The vaccine-only group peaked at 53.13 percent protected on day 7, fell to 28.13 percent on day 14, recovered to 34.38 percent on day 21, and stood at 37.50 percent on day 28. Fewer than four in ten sheep cleared the 1:128 threshold at the end of the observation window. This is young stock receiving a primary course, so the figures describe that specific setting.
What antibody titer counts as protective for FMD?
The threshold used here was 1:128, following the national standard for FMD vaccine efficacy evaluation. Titre was measured by liquid-phase blocking ELISA against serotype O and expressed as the reciprocal of the highest dilution producing an optical density above the 50 percent blocking threshold. Animals reaching 1:128 or above were counted as immune-qualified.
Were the sheep healthy before the trial started?
Yes. All 96 animals passed quarantine inspection, tested negative for FMDV serotype O antibodies below 1:8, and had no parasite ova on faecal examination. They had no history of FMDV infection and no recent use of immunosuppressive agents or anthelmintics. Feed during the trial contained no antimicrobials or anthelmintics, so the suppression observed cannot be blamed on pre-existing infection.
Can clostridial vaccination be given with the FMD vaccine?
The evidence here says no, at least not on the same day. The clostridial combination produced zero protected animals by day 28 and significantly lower titers at every sampling point. The clostridial vaccine stimulates antibodies against several Clostridium toxin types, and those antigens compete with the FMD component for immune resources. Giving it in a separate session avoids that competition.
Which causes more suppression, ivermectin or a second vaccine?
Ivermectin, according to this trial. The ivermectin group showed significantly greater suppression than the clostridial group across the observation period. On day 28 the ivermectin group had 6.25 percent protected while the clostridial group had none, but titers declined faster and further in the ivermectin group overall. The two mechanisms are different and they add together.
What does this mean for deworming and vaccination in cattle?
The trial used sheep, so the numbers transfer with caution rather than confidence. The mechanism, antigen competition plus immunomodulation, is not species-specific, and the same combination practice is common in cattle and goat production. Until a dose-separated study is run in cattle, the safe assumption is that separating the procedures costs less than a failed vaccination round.
Does the FMD vaccine protect immediately after injection?
No. In this trial protection peaked on day 7 at 53.13 percent and declined afterwards in the vaccine-only group. That pattern argues against relying on a single early sample as proof of protection, and it argues for confirming titers later in the course. A primary course in young stock may need more than the standard window before herd-level protection is reliable.
