Katie Spence, deputy director of the UK Health Security Agency in the region, issued the warning amid concerns over complacency.
But the health boss said the rise has not let to a significant increase in hospital admissions or deaths, due to the Covid-19 vaccines.
She said: "It’s been a number of months since the easing of Covid-19 restrictions and we are all enjoying some normality after a challenging two years which impacted all corners of life. As we now look forward to life without restrictions and head into the social summer holiday period, we must keep in mind that the virus has not gone away.
"In fact, in recent weeks we have seen a rise in cases in the West Midlands, with a shift in the dominant strain from the Omicron BA.2 variant. The latest data indicates that Omicron BA.4 and BA.5 now account for more than half of rising Covid-19 cases in the UK and are driving the recent increase in infections.
"We are fortunate that so far the rise in cases has not led to a significant increase in hospital admissions or deaths and this is down to the efficacy of the vaccine and the incredible efforts of people across the country getting vaccinated."
Ms Spence said people need to remain vigilant, take precautions and ensure they're up to date with their Covid-19 vaccines and people should still stay at home if they have the virus.
People should meet others outdoors this summer and wear face coverings in crowded, enclosed spaces, or on public transport and in shops – and make sure to wash their hands regularly.
"We need to continue to keep ourselves and our loved ones safe and vaccination is the best form of defence we have. It’s never too late to get vaccinated," she said.
"Let’s enjoy the summer and our regained freedoms but keep in mind that Covid-19 hasn’t gone away and we all need to do our bit to live safely."