- South Africa has doubled the interval between the first and second dose of the Pfizer vaccine, from 21 days to 42 days.
- A preprint study found that people who got their jabs 12 weeks apart had more than triple (3.5 times) as many antibodies in their blood than those who were immunised three weeks apart.
- Countries such as the United Kingdom and Canada also extended dosing intervals for the jab.
In South Africa, people who received their first shot of the Pfizer COVID vaccine will now have to wait six weeks before returning for the second jab.
This follows updated guidance issued by the national health department a month ago, in light of new data showing a longer delay between doses could offer more protection.
Until last week, the Pfizer vaccines were the main jabs being rolled out in South Africa — with just over 1.5-million people receiving their first shot. On Thursday, 300 000 Johnson & Johnson jabs arrived and this week Aspen Pharmacare will release an additional 1-million doses.
This follows delays in getting Johnson & Johnson jabs into the country, after some consignments were unusable because of low production standards. As a result, there is more pressure to increase the use South Africa gets out of the remaining vaccines in its arsenal.
We look at the evidence behind the three-week extension between doses, what this means for your follow-up appointment and how it could help alleviate the pressure on the country’s vaccine supply.
The Pfizer vaccine was designed as a two-dose shot. The manufacturer recommended the jabs be spaced three weeks apart.
When the vaccine was being tested in a clinical trial, the doses were given at this interval (the time between the shots). This means that the trials results — of 95% efficacy in preventing disease — only applied to the shots when used in this way.
In fact, in a statement issued in March, Pfizer re-emphasised that its vaccine had not been studied using an extended dosing interval (or the time between the two shots) despite some governments deciding to recommend alternative spacing for the shots.
But in light of restricted vaccine supplies and growing evidence to support a longer delay between doses, South Africa has opted to double the wait time between shots. This way, the country is able to give as many people as possible first doses straight away, so that they get at least partial protection against COVID.
In a notice shared on 19 May by the health department’s director-general Sandile Buthelezi, the elongated time frame was attributed to “emerging evidence to support a 42-day interval between the first and second doses”.
This also followed a recommendation from the ministerial advisory committee on COVID vaccines that the time between doses be extended if there was a shortage of jabs.
The new time frame applies to everyone who has received the shot — so even if you were vaccinated before 19 May (the day on which the circular was issued), your original follow-up appointment will be shifted by three weeks. People who were previously told to return for their second dose after 21 days, will receive an electronic vaccination data system (EVDS) notification in the form of an SMS about the new timeline.
Messages with the date of appointments for second doses are, however, only sent out three days in advance.
Waiting to give people the details for their appointment allows for more vaccination sites to come online, which means people can then be allocated to places that require less travel and can reduce the time it takes to get your jab, explains Milani Wolmarans, acting chief operating officer in the health department.
South Africa began phase two of its national vaccine roll-out on 17 May, so the first people will return to be fully immunised with the second shot of the Pfizer jab on 28 June.
A gamble that paid off: Why some countries changed policy without science
Despite the vaccine only being formally tested with a 21-day gap between doses, some countries decided to deviate from this plan.
Although not as extreme as other countries in their approach, the United States Centres for Disease Control and Prevention (CDC) has made allowance for the doses to be given a maximum of 42 days apart. This aligns with the updated guidance from South Africa’s health department.
Given the limited evidence available, the CDC recommends that the doses be given “as close to the recommended interval of three weeks as possible”. But when it is not possible for someone to receive their second dose within 21 days, the guidance allows for a delay of up to six weeks.
On the other hand, in December last year the United Kingdom began giving people their second Pfizer jab after 84 days.
There was no data to back up the change in the Pfizer dosing interval at the time.
The chief executives of the United Kingdom’s National Health Service (NHS) gave this explanation for their decision in a December 2020 letter to NHS staff: “Prioritising the first doses of vaccine for as many people as possible on the priority list will protect the greatest number of at risk people overall in the shortest possible time and will have the greatest impact on reducing mortality, severe disease and hospitalisations and in protecting the NHS and equivalent health services.”
Six months later, Northern Ireland, a constituent of the United Kingdom, recommended the two jabs be given a maximum of eight weeks apart instead of 12 weeks. The country’s health department says the recommendation to shorten the dosing interval is a move to help protect more people from the virus, especially in light of rising infections caused by the Delta variant (first identified in India).
The United Kingdom is not alone in its decision. Canada, similarly, opted to delay the roll-out of second doses so that more people can get their first dose while more vaccines are on the way. Canada’s national advisory committee on immunisation recommended the dosing interval be extended to four months between shots.
What does the research say?
A May preprint study was the first research to directly compare the strength of people’s immune responses after receiving the second dose of Pfizer after three weeks and after 12 weeks (84 days).
Participants on the extended dosing interval had a much stronger immune response than those on the standard three-week interval. Those who got their jabs 12 weeks apart had more than triple (3.5 times) as many antibodies in their blood than those who were immunised three weeks apart. Antibodies are proteins that help the body fight harmful pathogens such as viruses.
The small study included 172 participants all over the age of 80.
Ninety-nine participants got their second jab at three weeks, while the remaining 73 participants received their second shot 12 weeks later.
An earlier paper, published in Plos Biology in April found that delaying the second dose of the Pfizer vaccine to 12 weeks prevented more hospitalisations and deaths when compared with a three-week interval.
Although the paper points out that when compared to the Moderna — the other mRNA COVID vaccine — a shorter delay of between six to 12 weeks between Pfizer doses can yield greater results in terms of reducing hospitalisations and deaths.
This finding, however, relies on how long immunity lasts after the first dose.
The researchers studied two hypothetical scenarios, one in which immunity drops before the second dose, and one in which it doesn’t.
In the best case scenario where immunity doesn’t wane before the second dose, there were fewer infections, hospitalisations and deaths. In the worst case scenario, the benefit of delaying the second dose was far lower since fewer infections, hospitalisations and deaths were prevented.
The decrease in hospitalisations and deaths were based on the assumption that every day, 30 people were being vaccinated for every 10 000 people in the population. The researchers argue that as immunisation programmes speed up and more people get the jab each day, the same reduction of deaths and hospitalisation would be achieved with a shorter interval.
Similar mathematical modelling done in Canada in an April preprint study compared dosing intervals of three and four months to a baseline of six weeks between jabs. The paper found that by extending the time between shots up to four months, there was a greater reduction in severe disease.
Ultimately, the projections showed that for older people (those above 75) the ideal gap between doses was 16 weeks (four months). While a longer time frame of six months was actually able to offer more protection for people between the ages of 20 and 74 years old.
This paper echoes the Plos Biology study in that it also found that it was more beneficial to extend the gap between doses when there is limited access to vaccines, because it allows for more people to be at least partially immunised over a shorter period of time.