How long does protection last from two Covid vaccine doses?

The UK government is launching a coronavirus vaccine booster campaign to tackle waning immunity.

It forms a key part of its “autumn and winter plan" to deal with the virus in England over the coming months.

Heath secretary Sajid Javid referred on Tuesday to evidence that the protection given by vaccines “reduces over time, particularly older people who are at greater risk”.

So, from next week, boosters will be offered to priority groups including over-50s, people with underlying health conditions and health and social care workers.

The UK is now one of 10 countries, including France, running a booster campaign of third jabs, with either a full dose of Pfizer or a half dose of Moderna being offered – regardless of which one people had previously. 

AstraZeneca will be offered when Pfizer or Moderna doses are not possible, for example due to allergies.

On Thursday last week, a Public Health England (PHE) study on vaccine duration was considered by the Scientific Advisory Group for Emergencies (Sage), with the document made public on Tuesday. Here are the key findings.

How long does immunity last from two Covid vaccines?

The report considers the “VE” (vaccine effectiveness) of the Pfizer and AstraZeneca jabs, as full data were not available for the Moderna vaccine. Here, it is broken down by category.

Symptomatic disease

Vaccine effectiveness against symptomatic disease in over 16s. (Yahoo News UK/Flourish)
Vaccine effectiveness against symptomatic disease in over 16s. (Yahoo News UK/Flourish)

After five months, both jabs are less likely to prevent symptomatic disease.

The report stated: “With both vaccines, waning of VE against symptomatic disease is seen from around 10 weeks, reaching just over 50% with AstraZeneca and just over 70% with Pfizer by 20-plus weeks.”

Hospitalisation

Vaccine effectiveness against hospitalisation in over 16s. (Yahoo News UK/Flourish)
Vaccine effectiveness against hospitalisation in over 16s. (Yahoo News UK/Flourish)

This is where the outlook starts to improve, as demonstrated by the flatter lines on the above chart.

The report stated: ”Waning against hospitalisation appears to be much more limited, in particular with the Pfizer vaccine where VE of around 95% continues to be seen beyond 20 weeks after vaccination.

“With the AstraZeneca vaccine, there appears to be some waning to just under 80% VE against hospitalisation from 20-plus weeks.”

Death

Vaccine effectiveness against death in over 16s. (Yahoo News UK/Flourish)
Vaccine effectiveness against death in over 16s. (Yahoo News UK/Flourish)

Ultimately, two doses of the vaccine continue to provide strong protection against death from Covid-19.

“Similar to hospitalisation, there appears to only be limited waning of VE against death,” the report said.

Age groups and hospitalisations

Vaccine effectiveness against hospitalisation by age groups and health status. (Yahoo News UK/Flourish)
Vaccine effectiveness against hospitalisation by age groups and health status. (Yahoo News UK/Flourish)

While the above points provide a useful overall picture for all over-16s, it is also important to consider vaccine effectiveness by older age groups, as this formed a key part of the decision to launch a booster campaign.

For the key metric of preventing hospital admissions, which is the overriding focus of the government’s autumn and winter plan, the study showed after 20 weeks…

  • A 4% reduction in effectiveness of Pfizer in over-65s (98.3% to 94.6%)

  • A 15% reduction in effectiveness of AstraZeneca in over-65s (93.7% to 78.6%)

  • A 23% reduction in effectiveness of Pfizer in clinically extremely vulnerable over-65s (94.6% to 71.4%)

  • A 20% reduction in effectiveness of AstraZeneca in clinically extremely vulnerable over-65s (79.3% to 59.4%)

  • Meanwhile, the study also indicated a 30% reduction – to about 70% – in effectiveness of Pfizer in over-80s, many of which received this vaccine in December and January with a three-week interval between doses

Speaking about the booster campaign at a Downing Street press conference on Tuesday, England's deputy chief medical officer Prof Jonathan Van-Tam said it "will make a very substantial impact on keeping the lid on things Covid-wise in terms of hospitalisations and deaths – and keeping pressure off the NHS this winter".