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Booster dose of 6 Covid vaccines is safe, increases immunity, shows study in Lancet

The study looked at safety, immune response and side-effects of seven vaccines — Oxford-AstraZeneca, Pfizer-BioNTech, Novavax, Janssen, Moderna, Valneva and Curevac.

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New Delhi: A booster dose of as many as six Covid-19 vaccines elicits strong immune responses in fully-vaccinated people, said a new study published in The Lancet.

The study was conducted on people who were vaccinated with either the Oxford-AstraZeneca (known as Covidshield in India) or the Pfizer-BioNTech jabs. This is the first randomised trial of boosters given after two doses of either vaccine.

Previous studies have shown that two doses of the Oxford-AstraZeneca and the Pfizer-BioNTech vaccines elicit 79 per cent and 90 per cent protection, respectively, against hospitalisation and death after six months.

However, some studies have also indicated that protection against Covid-19 infection wanes over time. This has led the vaccine manufacturers to advocate a third ‘booster’ shot to protect the most vulnerable populations.

There is little data though on the comparative safety of Covid vaccines, and the immune responses they stimulate, when given as a third dose.

The new study looked at safety, immune response and side-effects of seven vaccines — Oxford-AstraZeneca, Pfizer-BioNTech, Novavax, Janssen, Moderna, Valneva and Curevac.

All the booster vaccines increased the immune response when administered after two doses of Oxford-AstraZeneca shots. However, among those who had received two doses of the Pfizer-BioNTech vaccine, only Oxford-AstraZeneca, Pfizer-BioNTech, Moderna, Novavax, Janssen and Curevac induced an immune response.

Valneva didn’t elicit an effective response when used as a booster.

“The side effect data show all seven vaccines are safe to use as third doses, with acceptable levels of inflammatory side effects like injection site pain, muscle soreness, fatigue,” Saul Faust, trial lead from the University Hospital Southampton, UK, said in a statement.

Also read: 2 Omicron cases detected in Karnataka, first in India, says health ministry

How the trial was conducted

The team conducted a phase-2 trial of seven booster vaccines, with the third doses given 10-12 weeks after initial two doses of the Oxford-AstraZeneca or the Pfizer-BioNTech shots.

The trial involved 2,878 participants recruited at 18 United Kingdom sites between 1 and 30 June. 

Participants had received their first doses of Oxford-AstraZeneca or the Pfizer-BioNTech vaccines in December 2020, or January, or February, and second doses at least 70 days (for Oxford–AstraZeneca) or 84 days (for Pfizer-BioNTech) before enrollment.

The team looked at adverse effects seven days after receiving a booster, and levels of antibodies targeting the spike protein of the virus after 28 days. They also looked at the response of T cells — which play a key role in the immune response to viral infection — to Alpha, Beta, and Delta variants of SARS-CoV2.

Increases in anti-spike protein antibody levels after 28 days varied across the vaccines. These ranged from 1.8 times to 32.3 times higher, according to the booster vaccine used after two doses of the AstraZeneca vaccine.

The range was 1.3 times to 11.5 times higher on booster after two doses of the Pfizer-BioNTech vaccine.

Significant T-cell responses were reported in several combinations, the researchers said. At 28 days, all booster results were similar for participants aged 30-69 years and those aged 70 years or older.

“It’s important to note that these results relate only to these vaccines as boosters to the two primary vaccinations, and to the immune response they drive at 28 days,” Faust added. “Further work will generate data at three months and one year after people have received their boosters, which will provide insights into their impact on long-term protection and immunological memory,” he said.

“We are also studying two of the vaccines in people who had a later third dose after 7-8 months although results will not be available until the new year.”

Reactions to all seven vaccines were similar, with fatigue, headache, and injection site pain most often reported.

Also read: South Africa in talks with Pfizer, Merck for Covid pills amid Omicron concerns


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