Whether you get it from a vaccine or an infection, Covid-19 immunity does not last forever, say researchers who, after examining 40 studies, found that on average, a month after two doses, vaccine effectiveness was 53% in protecting against symptoms of the virus – and just 9% after six months.
The scientists, led by a team from Italy, analysed 40 studies that documented people’s vaccination status and their subsequent infections with Covid-19, confirmed by lab tests. The studies included data from both the Delta and Omicron surges.
TIME reports that overall, one month after people received two doses of either the mRNA vaccine (from Moderna or Pfizer-BioNTech), the vaccine from AstraZeneca, or the shot from Sinovac, effectiveness was 53% in protecting against symptoms of Covid-19. (There were differences among the vaccines, with Moderna’s primary series of two shots showing the highest effectiveness of 62% one month after the series, and Sinovac’s demonstrating the lowest effectiveness at 32%.)
After six months, the overall effectiveness of the vaccines dropped further to 14%, and to 9% after six months.
This waning was greater during the Omicron wave than during the Delta wave, suggesting the vaccine was less effective against Omicron.
Booster doses after the primary series restored protection back to levels achieved just after the primary vaccination, but this protection waned too, at a rate similar to that after the primary series, dropping from 60% at one month after the booster dose to 13% at nine months.
This drop in efficacy corresponded to rates of lab-confirmed positive tests for Delta and Omicron infections.
The studies in the review (published in JAMA Network Open) did not delve into how well the vaccines protect against more severe disease, hospitalisations, and deaths due to Covid-19; other studies to date have shown that protection against more serious outcomes wanes much more slowly than against symptomatic infection, and that the shots continue to protect pretty well against these more dire events.
“This study shows that the protection [from vaccines] is very high at the beginning, but it wanes quickly,” said Marco Ajelli, associate professor of epidemiology and biostatistics at the Indiana University School of Public Health and one of the study’s co-authors.
“That’s exactly in line with what we observe for influenza.”
In fact, he said, the flu vaccine and its immunisation schedule could serve as a useful model for determining when Covid-19 vaccines should be given to keep protection as robust as possible.
“We know we get an influenza shot every year because the protection from last year’s shot doesn’t work through this year,” he sid.
“The situation for Covid-19 will be very similar…we need to get into a cycle or loop to get a new dose to boost protection.”
Public health experts expect that Covid-19 cases will continue to ebb and flow around the world, and it’s not clear yet whether infections will peak during classic respiratory virus seasons, as do flu and colds.
But it’s reasonable to assume that they might, given that SARS-CoV-2 is also a respiratory virus that targets the lungs. Getting an updated dose will serve two purposes: protecting the individuals who are vaccinated, and also protecting the communities in which they live by creating a wall of immunity that reduces the risk that the virus can spread from person to person.
“Without repeated booster doses for the population, I think the virus circulation will be left uncontrolled,” said Piero Poletti, senior researcher at the centre for health emergencies of the Bruno Kessler Foundation in Italy and another co-author of the study.
That could lead to continued infections and disease, and potentially provide the virus with more opportunities to mutate into more virulent forms.
As with the yearly flu shot, however, the key to developing an effective Covid-19 shot is to target the right strain or strains based on the version of the virus most dominant at the time.
That takes a bit of educated conjecturing and some guesswork – as it does for the annual flu vaccine.
In June, the US Food and Drug Administration will convene its panel of vaccine experts to figure that out: the first step toward turning Covid-19 into a vaccine that’s updated and administered on a fixed schedule.
Study details
Evaluation of Waning of SARS-CoV-2 Vaccine–Induced ImmunityA Systematic Review and Meta-analysis
Francesco Menegale, MSc1,2; Mattia Manica, PhD1,3; Agnese Zardini, PhD1; et al
Published in JAMA Network Open on 3 May 2023
Abstract
Importance
Estimates of the rate of waning of vaccine effectiveness (VE) against COVID-19 are key to assess population levels of protection and future needs for booster doses to face the resurgence of epidemic waves.
Objective
To quantify the progressive waning of VE associated with the Delta and Omicron variants of SARS-CoV-2 by number of received doses.
Data Sources
PubMed and Web of Science were searched from the databases’ inception to October 19, 2022, as well as reference lists of eligible articles. Preprints were included.
Study Selection
Selected studies for this systematic review and meta-analysis were original articles reporting estimates of VE over time against laboratory-confirmed SARS-CoV-2 infection and symptomatic disease.
Data Extraction and Synthesis
Estimates of VE at different time points from vaccination were retrieved from original studies. A secondary data analysis was performed to project VE at any time from last dose administration, improving the comparability across different studies and between the 2 considered variants. Pooled estimates were obtained from random-effects meta-analysis.
Main Outcomes and Measures
Outcomes were VE against laboratory-confirmed Omicron or Delta infection and symptomatic disease and half-life and waning rate associated with vaccine-induced protection.
Results
A total of 799 original articles and 149 reviews published in peer-reviewed journals and 35 preprints were identified. Of these, 40 studies were included in the analysis. Pooled estimates of VE of a primary vaccination cycle against laboratory-confirmed Omicron infection and symptomatic disease were both lower than 20% at 6 months from last dose administration. Booster doses restored VE to levels comparable to those acquired soon after the administration of the primary cycle. However, 9 months after booster administration, VE against Omicron was lower than 30% against laboratory-confirmed infection and symptomatic disease. The half-life of VE against symptomatic infection was estimated to be 87 days (95% CI, 67-129 days) for Omicron compared with 316 days (95% CI, 240-470 days) for Delta. Similar waning rates of VE were found for different age segments of the population.
Conclusions and Relevance
These findings suggest that the effectiveness of COVID-19 vaccines against laboratory-confirmed Omicron or Delta infection and symptomatic disease rapidly wanes over time after the primary vaccination cycle and booster dose. These results can inform the design of appropriate targets and timing for future vaccination programmes.
TIME article – Here's How Long COVID-19 Vaccine Immunity Really Lasts (Open access)
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