Why researchers support single Covid vaccine dose

Walking into a Covid-19 ward is a nightmare that can best be told by those who have tested positive and come out of it alive.

With the new developments in vaccines and some countries already administering jabs, shortages have been a glaring global issue.

Scientists now want a strategy that will help in limiting the stock-outs by giving just one dose, instead of two, to patients who have tested positive.

If their findings are viable after a peer-review and published in a scientific journal, then this plan will be a saviour.

Francis Ndung’u, an immunologist who was not part of the study, says this data is only limited to the two vaccines that are part of the study: Pfizer and Moderna.

“These considerations should not be to any vaccines - with the caution that data is only available for the Pfizer and Moderna vaccines for now,” he said.

The two vaccines in the study received the earliest efficacy results and were later approved for use.

“If you want to vaccinate as many people as possible with limited availability for vaccine vials, those who already have some immunity from a natural infection may not need the two doses,” he adds.

Kenya has so far recorded more than 100,000 cases of Covid-19 but to this date no vaccine has been deployed into the country.

The government has since made a list of priority groups that will get the jab first. Patients who have had Covid-19 are, however, not part of the list.

One shot enough

In the first study published in the pre-print server for Health Sciences, researchers took blood samples from 10 participants who had recovered from Covid-19. The participants were then vaccinated with the available vaccines.

Mr Ndung’u explained that should it be adopted, a recovered Covid-19 patient ought to be vaccinated “as the response from infection decays over several months”–and that one shot may be just enough.

Questions have been raised as to whether people who have already tested positive for the new variants are not likely to have an effective vaccination result. The study explains that the variants arising from the mutations could be culpable for inefficiency as they have observed in their trials based on the South African variant.

“Antibodies induced by infection decay over time – lasting for several months during which they could be protective to both strains but may be better against the strain they were infected with,” explained Mr Ndung’u.

The researchers found that the variant named B.1.351 has multiple mutations no wonder the high transmission rate as observed in South Africa and Brazil.

“In agreement with another report (the variant) was resistant to neutralisation by several donors previously infected with Sars-Cov-2,” said the researchers.

Antibody response

Ndung’u agreed that the vaccine amplified antibody response could be effective against different strains.

“The word amplified here is important because immunising a previously infected individual gives a bigger response than immunising someone who was not previously infected,” he said.

In the second study, about 109 individuals who were both positive and negative were vaccinated against Covid-19 disease.

After close to nine to 12 days post-vaccination, patients who had not contracted the virus had a relatively low and varying coronavirus antibody response. On the contrary, those who had been positive responded between the fifth and the eight day.

“Individuals with pre-existing Sars-Cov-2 (coronavirus) immune responses (as evidenced by Sars-Cov-2 antibodies) rapidly develop uniform, high antibody titers within days of vaccination,” said the study.

“For individuals with pre-existing immunity to Sars-Cov-2 the first vaccine dose likely immunologically resembles the booster dose in naïve individuals (those who are negative and have never contracted the disease).”

The Centres for Disease Control and Prevention in October last year said cases of reinfection of Covid-19 exist but are very rare. They went on and advised everyone regardless of their current or previous health status to still hold on to the containment measures.

This, however, will only be of use to the country if we procure Pfizer and Moderna vaccines as well. That, Ndung’u says, will then be a good consideration.

“We have to be clear that these studies only apply for the mRNA vaccines from Pfizer and Moderna. It’s likely that Kenya will go for other vaccines like the Oxford-AstraZeneca. Similar studies have not been done for that vaccine but the concerns will be the same and so it would be good to do those studies with the Oxford vaccine too - as we can save the limited doses for those that need them the most,” explained Ndung’u.