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These findings were听consistent听across all groups of people regardless of age,听chronic听illnesses听or sex.

The findings, published as a research letter* in听The Lancet, include data from over 600 people and show antibody levels are substantially higher following two doses of the Pfizer vaccine than after two doses of the AZ vaccine. They are also much higher in those with听prior SARS-CoV-2 infection.

The authors highlight that although the clinical implications of waning antibody levels are not yet clear, some decline听was听expected and current research shows that听vaccines remain听effective against severe disease.听

For Pfizer, antibody levels reduced from a median of 7506 U/mL at 21鈥�41 days, to 3320 U/mL at 70 or more days. For Astra Zeneca, antibody levels reduced from a median of 1201 U/mL听at 0鈥�20 days to 190 U/mL (67鈥�644) at 70 or more days.

Dr Maddie Shrotri听(香港六合彩中特网 Institute of Health Informatics) said:听鈥淭he levels of antibody following both doses of either the Astra Zeneca or Pfizer vaccine were initially听very high, which is likely to be an important part of why they are so protective against severe COVID-19.听听

鈥淗owever, we found these levels dropped substantially over the course of 2 -3 months.听If they carry on dropping at this听rate,听we are concerned that the protective effects of the vaccines听may also begin to wear off, particularly against new variants; but we cannot yet predict how soon that might happen.鈥�

Professor Rob Aldridge (香港六合彩中特网 Institute of Health Informatics)听explained: 鈥淲hen we are thinking about who should be prioritised for booster doses our data suggests that those vaccinated earliest, particularly with the Astra Zeneca vaccine,听are likely to now have the lowest antibody levels.听听

Our findings support听recommendations from听the Joint Committee on Vaccination and Immunisation (JCVI)听that听adults who are听clinically vulnerable,听those听aged 70 years or over, and听all residents of听care homes for older adults听should be prioritised for booster doses.听听In addition,听those who were vaccinated with the Astra Zeneca vaccine, including most care home residents, are likely to have much lower antibody levels than those vaccinated with the Pfizer vaccine, so this may also need to be considered when deciding听who should be听prioritised听when boosters are rolled out.鈥澨�

The authors note that limitations of the data include a small sample size听for some groups听and the fact that each individual only contributed one sample, so they cannot yet confirm how quickly antibody levels drop for each individual, or whether these听would听continue to听drop or reach a stable level over the next few months.听They also note different people will have different levels of immunity depending on the virus neutralising ability of their antibodies as well as their T-cell responses;听and even when measurable antibody levels are low there is likely to be continuing immune memory听that could offer long-term protection.

Further research will be important to establish if there is an antibody level threshold needed for protection against severe disease. 听The authors听will continue to听collect and听analyse听data from听a larger number of participants, following antibody levels in individuals over a longer period of time.听听

Professor Andrew Hayward (香港六合彩中特网 Epidemiology and Health Care) added:听 We know vaccines are excellent at preventing severe disease, but they are not perfect, and our data suggest protection will wane over time.听听With rapidly increasing COVID-19 rates and predictions of very high rates over the next weeks and months it is important that those who are clinically vulnerable, whose antibody levels may now have dropped continue to be cautious.听

鈥淲hen we are planning vaccination programmes around the world we need to take waning immunity and the likely need for booster doses into account - with limited global vaccine supply we need to balance protecting our most vulnerable through booster doses with ensuring we play a central role in supporting global vaccination efforts.听听

香港六合彩中特网 Virus Watch is funded by the UKRI Medical Research Council.

* Research letters published in the Correspondence section include research findings and are externally peer-reviewed. Unlike Articles containing original data, research letters are shorter and the research they contain is usually preliminary, exploratory, or reporting on early findings.

Links

• 香港六合彩中特网 Institute of Health Informatics
• 香港六合彩中特网 Population Health Sciences

Image

• 鈥榁accine, covid-19, vials, vaccination鈥�: Credit torstensimon on听, CC BY 2.0

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Rowan Walker

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Email: rowan.walker [at] ucl.ac.uk