The UK’s milestone of issuing 25m vaccine doses has been dampened by news that the vaccine rollout will be slowed down come April. 

A letter from the NHS in England states that volumes for first doses of the vaccine will be “significantly constrained” for four weeks from the end of March. 

At a Downing Street press conference after the letter emerged, health secretary Matt Hancock insisted the UK is still “on course” to ensure everyone aged 50 and over will be able to get vaccinated by April 15.

He has since confirmed the delay is due to a need to “retest the stability” of a batch of 1.7m doses of the Oxford/AstraZeneca vaccine and that a delay in a shipment from India has impacted supply.

So how will the vaccine slowdown affect you?

In short: it depends how old you are. Those aged 50 and over can expect to have their vaccine as normal.

But if you’re 49 and under – without an underlying medical condition – and you had hopes of having your jab before April, you should expect not to. Although if you are called up to have the jab, it’s definitely worth accepting the offer.

The government has confirmed people in their 40s are likely to have to wait until May to get their jab. 

Matt Hancock has said the government is committed to all adults being able to get the jab by the end of July – and added they are still on track to deliver on that commitment.

This was reiterated by a Department of Health and Social Care spokesperson (DHSC), who told HuffPost UK: “The vaccination programme will continue in the coming weeks and more people will continue to receive first and second doses.

“As has been the case since the programme began, the number of vaccinations carried out over time will vary due to supply – but we remain on track to offer a first vaccine to over 50s by 15 April and all adults by 31 July.”

The letter from the NHS, which alerted people to the delays, states those “aged 49 years or younger should not be offered vaccination” unless they are in a higher priority group, such as being clinically vulnerable, unpaid carers, or frontline health and care workers.

Based on this information, if you’re aged 49 years or younger without any pre-existing conditions, you probably won’t be called up for the vaccine until May. 

This is because those who have had their first dose of the jab will need to be prioritised for their second doses – as they are more at risk of serious illness and death from Covid-19. It’s likely that April will see the number of second jabs taking place exceed the number of people having their first jabs.

With different postcodes making more headway than others with the vaccination rollout, some GPs are confused about what they’re meant to do now. 

Dr David Lewis, co-clinical director of Central Liverpool Primary Care Network, says they have been following guidance by inviting people at risk first, and not offering second doses until 11 weeks after the first. But now they have surplus vaccine and they’re not sure what to do with it.

“We’ve invited all our eligible patients – everyone 50 years and over, and all adults with underlying conditions that put them at higher risk of Covid,” he says.

“We’ve done outreach vaccination for homeless people, people with learning disabilities, asylum seekers, in a community centre and in a mosque. We have a team of people phoning patients every day; but we still have appointments available, and spare vaccine.”

Inviting people for their second vaccine earlier is “strongly discouraged” by the NHS, he explains, and inviting younger adults is also forbidden.

The alternative is to waste the leftover vaccine. “This would be a tragedy,” he continues. “What should we do?”

What about the Moderna and Novavax vaccines?

Some scientists have been asking what has happened to the Moderna jab, which was given a vague rollout date of “spring” back in January by the government. Another vaccine, Novavax, is currently being assessed by the MHRA and could be approved for use in a matter of weeks. 

Professor Lawrence Young, an expert in molecular oncology from Warwick Medical School, says the UK is now “in a very precarious situation”.

Vaccine supply “was always going to be challenging”, says Prof Young – particularly with the current rates of daily vaccinations – but the UK is “limited” by having just two approved vaccines currently in use, he adds.

“Five million doses of the Moderna vaccine, which was approved for use by the UK Medicines regulator (MHRA) in January, were secured for delivery in the spring,” he says. “Where are they? We have also secured 60 million doses of the Novavax vaccine which is currently awaiting regulatory approval.”

When HuffPost UK contacted the Department of Health and Social Care (DHSC) to ask about its rollout, the department was unable to share any further information on dates. But a spokesperson for Moderna told Reuters the vaccine is on track to be supplied to the UK in April.

Could delays have an impact on lockdown, too?

Robert Jenrick recently told the BBC the government has “every reason to believe that [vaccine] supply will increase in the months of May, June and July”.

However, it’s not yet clear whether the easing of lockdown measures could be delayed as a result of the slowdown.

Prof Young believes the situation could mean we need to revisit the timetable for easing out of lockdown – particularly as a significant proportion of the adult population (those aged 18-49) remain unvaccinated and there is a continued threat of more transmissible virus variants around the country. At time of writing, there are four variants of concern circulating in the UK.

Dr Simon Clarke, associate professor in cellular microbiology at the University of Reading, believes “the ripple effects [of delaying vaccination] could last for months”. 

“It will undoubtedly make the meeting of the target dates for lifting restrictions more difficult than they otherwise would have been,” he says.

“By pushing back the under-50s first doses, their second doses are also being pushed back. If full vaccination becomes required for holidays abroad or even more mundane things like going to the cinema, millions of younger people may end up being excluded from participating for the whole summer.”