People previously admitted to hospital or needing “continuous or repeated” steroid use because of asthma are to be prioritised for the Covid vaccine.
The most severe cases will fall into priority-group four, the “clinically extremely vulnerable”, who should have received a letter advising they shield.
And the government has now confirmed the remainder will be included in group six, the clinically “at risk”, those usually eligible for a free flu jab.
It follows patients’ calls for clarity.
The government said it was following independent experts’ advice.
Its nine priority groups are based on preventing deaths and protecting health and care staff.
Since age is the biggest risk factor for Covid deaths, the first three groups are:
And the government aims to vaccinate everyone in the first four priority groups by mid-February.
Group six, which the government has now confirmed will include all those who need a steroid inhaler or tablets for asthma, will be vaccinated after healthy over-65s but before anyone younger than that without health conditions.
And it is understood the government will aim to offer the jab to group six – and all over-50s – by May.
Asthma UK and British Lung Foundation chief executive Sarah Woolnough said: “We know that many people with asthma are confused about when they will get the vaccine and what priority group they fall into.
“We’ve been urging the government for some months to provide clarity on this, as we know it’s a worrying time for lots of people.
“And we now have more information.”
But, she added: “It may be hard to accurately identify everyone in this [priority-six] group.
“The government should err on the side of caution in decision-making and cast its net wide when making decisions about definitions, to ensure that people with asthma who are at risk won’t be missed.”
As well as being an indicator of how severe someone’s asthma is, steroids suppress the immune system, making it harder to fight off viruses.
Ms Woolnough said: “Reassuringly, evidence now shows that people with well controlled asthma that is not severe don’t seem to be at higher risk of dying from Covid-19.”
But some people with asthma have expressed concerns online about their wider health.
NHS England said it would be offering vaccines based on the government’s nine categories and patients’ medical records.