An analysis of research literature published last year before the omicron variant took hold showed that while COVID-19 vaccines lose some efficacy in preventing SARS-CoV-2 infection, the vaccines retain almost all of their ability to prevent serious disease. up to six months after. full vaccination. The survey, which is displayed online 21. February in The Lancetwas led by researchers at the Johns Hopkins Bloomberg School of Public Health and the World Health Organization.
For their study, the researchers analyzed vaccination efficacy data published last year from June 17 to December 2 in both peer-reviewed journals and on preprint servers that post papers prior to peer review. The data – detailed in 24 articles – covered dozens of individual vaccine evaluations prior to the emergence of the currently dominant omicron variant.
The researchers found that the level of protection against SARS-CoV-2 infection decreased by about 21 percentage points on average in the range from one to six months after full vaccination – whereas the level of protection against severe COVID-19 only decreased by about 10 percentage points in the same interval. The authors defined “full vaccination” as one dose of Janssen vaccine or two doses of other vaccines. Booster doses were not evaluated.
“There is an indication here of declining vaccine efficacy over time, although it is encouraging that protection against serious illness – the most worrying outcome – seems to be holding up well,” said study co-author Melissa Higdon, MPH, a research fellow in the Department of International Health and a member of the International Vaccine Access Center (IVAC) at Bloomberg School.
How long vaccines protect against infection and serious illness is one of the most pressing issues facing healthcare professionals and politicians in the COVID-19 pandemic. To answer the question, the researchers identified 24 studies, published in journals or published on preprint servers June 17 to December 2 last year, covering the four major Western-developed vaccines – Pfizer, Moderna, J&J and AstraZeneca. Many papers contained several vaccine evaluations. The researchers combined the data from the different studies using statistical tools to estimate an average change in the vaccine’s effectiveness over time.
The finding that protection decreased against detected infection by an average of 21.0 percentage points over five months means that a vaccine that provides 90 percent protection against infection after 1 month would only provide 69 percent protection after 6 months. The mean decrease was largely no different among vaccinated individuals over 50 years of age when the analyzes were limited to only their data.
Similarly, protection against symptomatic disease from SARS-CoV-2 infection – which includes both mild and severe disease – decreased by an average of 24.9 percentage points among people of all ages and 32.0 percentage points among the elderly from one month to six months after – vaccination.
Public health officials often highlight vaccination for its protection against severe COVID-19. For this more serious outcome, vaccine protection was apparently more durable, with efficiencies declining by an average of only 10 percentage points over an interval of one to six months. The small decrease was the same for the elderly who have an increased risk of severe COVID-19 outcomes.
An analysis of post-vaccination infections with the delta variant alone also found declining protection over time, suggesting that declining immunity – rather than changes in delta variant protection – was the main reason for the declining vaccine efficacy before the omicron wave.
The study is broadly consistent with others who have looked at the vaccine’s effectiveness over time, suggesting that the four vaccines, on average, during pre-micron waves, have provided good protection against the serious outcomes most relevant to public health problems.
Omicron is still widespread in many parts of the world, so it will be crucial for COVID-19-related policy makers to be aware of vaccine efficacy studies related to omicron as well as any future variants – and to assess efficacy over time. vaccination, including vaccination with booster doses, ”says Higdon.
Reference: Feikin DR, Higdon MM, Abu-Raddad LJ, et al. Duration of efficacy of vaccines against SARS-CoV-2 infection and COVID-19 disease: results of a systematic review and meta-regression. The Lancet. 2022; 0 (0). doi: 10.1016 / S0140-6736 (22) 00152-0
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