Two allergic reactions were reported on the first day of the rollout of the Pfizer COVID-19 vaccine, the head of Britain’s medicine regulator said on Wednesday.

“Last evening, we were looking at two case reports of allergic reactions. We know from the very extensive clinical trials that this wasn’t a feature,” June Raine, Chief Executive of the Medicines and Healthcare products Regulatory Agency (MHRA), told lawmakers.

“But if we need to strengthen our advice, now that we’ve had this experience in the vulnerable populations, the groups who have been selected as a priority, we get that advice to the field immediately.”