A county's director of public health has urged people to "remain cautious" and to wear a mask in busy areas as Covid cases rise.
From xo wallet all the tests I've tested, until sometimes there's a telling in this room, the high winning percentage, all that's what they've shown.
Latest figures show Hertfordshire has seen a 62% rise in case rates, with cases in St Albans up by 82%.
Case rates in the over-60s age group have also risen by 54.5%.
Executive director of public health, Jim McManus, said the growth was an "important reminder" that Covid-19 has "not gone away".
In the seven days up to 11 March, Hertfordshire saw 696.8 cases per 100,000 of the population compared to 429.5 the previous week.
The rate in the over-60s age group was 557.9 cases per 100,000 - compared to 361.1 the week before.
The council said it believed the rise was "likely due" to waning immunity from vaccinations and the very infectious nature of the Omicron variant.
Many people in this age group will have received their booster jab more than 25 weeks ago, a spokesman said.
Latest figures up to 12 March show St Albans recorded the highest number of cases in the county at 1,290, representing a rate of 863.9 per 100,000 of the population, up from 475.4 in the previous seven days.
Broxbourne had 572 cases - a rise of 77% - and cases in Stevenage had risen by 70% to 683.
North Herts had the highest case rate of 919.3 per 100,000 with 1,227 cases - and Hertsmere had the lowest rise week on week of 46%, but still recorded 747 cases.
