Syringes are filled with Astrazeneca’s vaccine in the pharmacy.

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LONDON – An alternative to the Oxford-AstraZeneca Covid-19 vaccine to be offered to people under 40 in the UK as concerns about the link to rare blood clots continue to weigh on adoption.

Speaking at a news conference on Friday, Professor Wei Shen Lim, chair of the UK’s Joint Committee on Vaccination and Immunization (JCVI), said the agency had updated its recommendations for adults under 40.

“Building on our previous recommendations, we now recommend offering unvaccinated adults aged 30 to 39 who do not have an underlying health condition that poses a higher risk of severe Covid-19, preferably an alternative to the AstraZeneca vaccine is possible” he said, adding that this would only be the case if “there was no substantial delay in vaccination”.

He noted that the AstraZeneca vaccine was easier to transport and store than some of the alternative vaccines approved for use, which would affect how the new recommendations for those under 40 would be applied.

“In certain situations it may be the only viable vaccine that can be offered and in those circumstances it should indeed be the vaccine of choice,” he explained, adding that the advice was also of good Covid-19 infection control and one Dependent on good availability of alternative vaccines and strong vaccination in the UK.

Rare blood clots

A very small number of people who have been vaccinated with the AstraZeneca vaccine have had blood clots.

Labeled “extremely rare” by health officials, it is characterized by blood clots accompanied by low platelet counts.

As of April 28, the UK Medicines and Health Products Regulator (MHRA) had received 242 reports of large blood clots associated with low platelet counts that occurred after a dose of the AstraZeneca vaccine.

There were 10.5 cases of low platelet count blood clots per million first doses of the AstraZeneca shot, the drug regulator said in its latest report on the side effects of the Covid-19 vaccine. Dr. June Raine, executive director of MHRA, said Friday that the ratio for second doses had dropped to one in a million.

The death rate from rare blood clots was 20%.

In early April, the UK announced that it would offer people under 30 an alternative to the Oxford-AstraZeneca vaccine, which was approved for use in the country in late December.

Benefits versus risks

Raine emphasized during Friday’s press conference that the agency had not changed its approval of the AstraZeneca vaccine as the benefits continue to outweigh the risks for the vast majority of people.

“The balance between benefits and risks is very good for older age groups, but more balanced for younger age groups,” she said.

According to the MHRA report, updated Thursday, the incidence of such blood clots was higher in younger adults. There have also been more reports of blood clots in women, although officials noted that this was not seen in all age groups and “the difference remains small”.

As of April 28, an estimated 22.6 million first doses and 5.9 million second doses of the AstraZeneca Covid-19 vaccine had been administered in the UK.

Both UK and EU drug regulators last month identified possible links between the vaccine and the rare blood clots. European Medicines Agency officials said most cases occurred in women under 60 within two weeks of being shot.

The World Health Organization and the International Society on Thrombosis and Hemostasis have all stated that the benefits of giving the Oxford-AstraZeneca vaccine continue to outweigh the risks.

Reported links for rare nerve disorders

On Friday, the European Medicines Agency’s Safety Committee announced that it was analyzing data on cases of Guillain-Barre Syndrome (GBS) – a rare nervous system disorder – following vaccination with AstraZeneca’s Covid-19 vaccine.

GBS causes nerve inflammation and can lead to pain, numbness, weak muscles, and difficulty walking.

The regulator said their safety committee had asked AstraZeneca for more detailed data on cases reported after vaccination.

An AstraZeneca rep was not immediately available for comment when contacted by CNBC.