One Dose Of Pfizer Or Two, From Experts

A significant proportion of people over 80 may have only a “poor” immune response after a single dose of the Pfizer-Biontech vaccine, researchers have said. Three weeks later, one jab did not always produce the level of antibodies thought to be necessary to block infection. A second dose did lift them above this threshold, however.

Professor Ravi Gupta of Cambridge University,

who led the study, said that there was also anecdotal evidence that jarred with assurances from government advisers about the level of protection offered by one dose. He knew of two cases where people who had been vaccinated had later been admitted to hospital. “Certainly here in Cambridge we are seeing people who have been vaccinated coming into hospital with Covid-19 confirmed” he said.

The cases involved older people who were admitted to Addenbrooke’s Hospital in Cambridge, despite having been given the injection several weeks earlier. “You should have protection [by then], based on what we were told” Gupta added. “It may just be the tip of the iceberg. It’s important to know that we are seeing cases who have had vaccines.”

The professor and his team have suggested that rapid antibody tests could be used to identify older people who have responded less well to the initial jab and who should be prioritised for the booster shot. Their study, which is yet to be peer-reviewed, looked at 23 people, who had an average age of 82. Seven, all over the age of 80, had what was described as a “poor response” to a single vaccine dose.

The study did not show whether these people would have developed serious disease. “They might still get a much milder disease and they may not get very sick. We can’t say anything about severity, but they could get infected” Prof Gupta said.

Dr Dami Collier, the main co-investigator on the studies, said “Our data suggest that a significant proportion of people aged over 80 may not have developed protective neutralising antibodies against infection three weeks after their first dose of the vaccine. But it’s reassuring to see that after two doses, serum from every individual was able to neutralise the virus.” The second study has also not yet been peer-reviewed.

Dr Jonathan Stoye of the Francis Crick Institute, who was not involved in the research, said that it suggested that “some elderly individuals make relatively low immune responses to a single dose of vaccine” and that this may help create vaccine-resistant variants of the virus. This raises the possibility that, in some individuals, vaccine-elicited immune responses may be too low to completely block virus replication but high enough to drive selection of resistant viruses. In other words that sub-optimal levels of antibody are driving virus evolution.”

Azra Ghani, chair in infectious disease epidemiology at Imperial College London, said “With the South African variant now in the UK, it will be important to ensure that the most vulnerable groups are fully protected by the second dose. Given the high coverage of first doses that has now been achieved in the first four priority groups coupled with the very strong age-gradient in risk, this would be a good point at which to switch to scheduling second doses alongside continuing the wider roll-out of first doses to the next priority groups”.

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