Despite mounting evidence that people who got a traditional vector-based vaccine such as JnJ as a first shot had a stronger immune response against Covid-19 infection when boosted with an mRNA vaccine such as Pfizer or Moderna, homologous boosting with JnJ is still 100 times better than receiving no boost at all before the expected 4th wave hits the country.

This is according to Professor of Vaccinology Shabir Madhi. He was one of the leading experts on Covid-19 and vaccines taking part in this weekend’s virtual 25th annual conference of the KZNDHC Healthcare Institute where the current debate around JnJ boosters for healthcare workers (HCWs) was one of the hot topics under discussion.

It follows SAMA’s open letter to Health Minister Joe Phaahla last week in which concerns were expressed about government’s decision to roll out the Sisonke phase 2 JnJ boost trial without offering healthcare workers the choice of boosting with Pfizer despite evidence that a heterologous or ‘mix and match’ prime-boost schedule could potentially be more effective.

“While recent data show that JnJ followed by an mRNA vaccine such as Pfizer elicited higher antibody responses and produced a greater T-cell immune response, healthcare workers will still be better protected in the face of an expected resurgence than not taking any booster,” Prof Madhi stressed.

Also referring to accumulating data about the benefits of heterologous boosting, Co-National Investigator of the Sisonke study and SAMRC CEO, Prof Glenda Gray explained that when SAHPRA gave approval for the JnJ booster study, not enough data were available to justify heterologous boosting. However as more data become available, it will be discussed with the Department of Health and SAHPRA to decide if and when Pfizer boosters will be offered, she stressed.

Prof Gray said available evidence showed that the efficacy of boosting with JnJ two months after receiving the first shot was similar to that of receiving two doses of the Pfizer jab with safety and immunogenicity data supporting the homologous prime boost.

“As more data on the efficacy and safety of heterologous boosting become available, certain processes may come into place that will allow for mixing and matching including pharmaceutical companies submitting their dossiers to the relevant regulatory authorities before recommendations are made,” Prof Gray noted.

In a statement last week, the SAMRC said that it was aware of discussions to offer health workers a single booster dose of Pfizer. However, it emphasised that such a decision will only be formalised by the Department of Health in the coming weeks to months, and that their priority remains extending first vaccinations to all adults, and especially all those over the age of 50 years, by the end of the year.

In the meantime, the Sisonke booster study will continue until 17 December. Earlier, Acting Director-General of Health, Dr Nicholas Crisp explained that offering Pfizer as an alternative could delay the boosting process aimed at giving healthcare workers better protection in the event of a resurgence. He urged eligible frontline healthcare workers to go for their booster shots as quickly as possible to improve their level of protection before the next wave, emphasising that there is no doubt that the vaccine is the most dependable weapon against the pandemic.

Stating emphatically that he will wait for the Pfizer booster to become available rather than taking a second JnJ jab, Caprisa Director and government’s former chief adviser on Covid-19, Prof Salim Abdool Karim referred to recent studies suggesting that boosting a vector-based first shot (JnJ or AstraZeneca) with an mRNA vaccine offers better protection than two doses of JnJ or AstraZeneca. The one study – a nationwide cohort study of more than 720 000 individuals in Sweden and published in the Lancet Regional Health showed that people who received an mRNA booster (Moderna) after a single dose of JnJ saw their antibody levels rise 76-fold in 15 days, compared to an increase of just 4 times after an extra dose of J&J. In a preliminary study conducted by the National Institutes of Health in the US that included more than 450 adults, it was found that boosting with Moderna or Pfizer significantly increased antibody responses compared to two JnJ doses. The researchers of the study, which has not been peer-reviewed, concluded that heterologous prime boost strategies may offer immunological advantages that may optimise the extent and longevity of protection achieved with currently available vaccines.

However, conceding that it could take time before the Pfizer booster will become available for HCWs in South Africa, Prof Karim echoed the sentiments of Prof Madhi that two doses of JnJ will still offer better protection than a single JnJ shot.