Maternal antibody interference and vaccine timing in puppies.

• A. Start at 6–8 weeks and repeat every 3–4 weeks until about 16 weeks.
• B. Start at 12 weeks and annual boosters.
• C. Start at 4 weeks and every 2 weeks until 20 weeks.
• D. Start at 20 weeks only.

Answer: (A)

Maternal antibodies from the dam can neutralize vaccines in very young puppies, preventing their own immune system from mounting a proper response. Because the amount of these antibodies wanes at different times in different puppies, a staggered vaccination schedule is used to catch the period when the puppy’s immune system can respond once maternal interference declines. Starting at 6–8 weeks and repeating every 3–4 weeks until about 16 weeks provides multiple chances for seroconversion as maternal antibodies fade, giving reliable initial immunity. Starting later, at 12 weeks, leaves a longer gap of vulnerability before the puppy can respond; starting as early as 4 weeks is often blocked by maternal antibodies and yields unreliable protection; waiting until 20 weeks delays immunity too long and misses early life exposure risk. This schedule best balances early protection with the likelihood of an effective immune response.