1% of the population, and 8% of over 80s are on warfarin, and the vaccine has been given to hundreds of thousands by now, with no evidence of significant side effects. That doesn’t mean some people won’t have them, but it will be a tiny minority who do. Most people on warfarin have been monitored by their GPs pre and post vaccination to reduce any risks, and any adverse effects are being reported via the yellow card system so would be recorded and investigated if there was a pattern of incidence. If your partner is only being monitored every 12 weeks that presumably means he wasn’t monitored before his vaccine, which is worrying if his levels fluctuate?