Latest research on scheduling of two dose vaccines

Had your first Pfizer vaccine dose? Your second is due 42 days later

Since the start of phase 2 of South Africa's national vaccine rollout on 17 May, thousands of people have received a first dose of their two-dose mRNA Pfizer-BioNTech vaccine.

On 19 May, the National Department of Health announced that for people who have had a first dose of the Pfizer-BioNTech vaccine, the second dose or "booster shot" will now be given six weeks or 42 days later.

Originally, it was advised that the second dose would be given after three weeks or 21 days. The new 42-day period takes available clinical trial data on optimal efficacy of the Pfizer vaccine into account.

• Want to better understand why there is a need for a second dose - also called a COVID-19 vaccine booster shot? Find out more about this and current expectations about future COVID-19 vaccine booster shots.

Dr Noluthando Nematswerani is Head of the Discovery Health Centre for Clinical Excellence. She explains: "After you have received your first Pfizer-BioNTech vaccine dose, you will receive an SMS with a notification of the date of your appointment for the second vaccine dose. Please do not go for a second dose of the vaccine before 42 days have passed since your first dose. You will not be vaccinated until the 42-day period is over. Rest assured that the Ministerial Advisory Committee on COVID-19 Vaccines decided on this period through careful review of published clinical research, taking into account the best interests of the citizens of South Africa."

UK research: Stronger immune response when second COVID-19 vaccine dose is delayed to 12 weeks after first dose (versus having it three weeks later, as originally advised)

"New research has emerged from the United Kingdom (UK) in recent weeks showing that delaying second doses of this COVID-19 vaccine could boost antibody responses," explains Dr Nematswerani. "This started at the end of 2020 when a seemingly controversial decision was taken to delay to 12 weeks giving second doses of COVID-19 vaccines to people in the UK who'd had a first dose. It was controversial as, at the time, the manufacturers of the Pfizer-BioNTech and Oxford-AstraZeneca vaccines being rolled out in the UK recommended a three to four-week gap between doses. And this meant that people who'd had a first dose would only receive their second dose after this period."

"However, it was justified by a decision very much in the public interest - to get as many first doses as possible administered to as many people as possible - before second doses were given out. This meant a greater proportion of the elderly and at-risk population were at least partially protected from severe COVID-19 illness and death before moving on to giving people a second dose."

This decision seems to be supported by recent published data that found that the immune response in people over the age of 80 was three and a half times higher when their second vaccine dose was delayed to 12 weeks after the first dose," explains Dr Nematswerani. "A stronger immune response not only means heightened protection against the disease but also that protection against COVID-19 may last longer."

"At the end of the day, we are still dealing with a relatively new disease as well as new vaccines against it. This means that with time, we are gaining new insights into maximising the effectiveness of these vaccines against COVID-19. At all times our aim is to amplify the immune response and prevent severe illness and deaths in as many people as possible."

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