Why fully vaccinated people can catch Covid

LONDON – People fully vaccinated against Covid-19 are highly protected against serious infections, hospitalizations and death caused by the virus. But cases of coronavirus among the fully vaccinated – “revolutionary” Covid cases – are still seen among those who received two doses.

This happens for a number of reasons, experts note.

For starters, none of the vaccines being rolled out in the United States or Europe are 100% effective in preventing infection.

In addition, new strains of Covid such as the highly infectious delta variant – which is now widespread around the world – have complicated the picture of efficacy. There is also incomplete data on the duration of immunity against Covid after vaccination.

The alarm was sounded over the cases of Covid-19 when preliminary data in Israel – which had one of the fastest vaccination programs in the world – published in late July revealed that the Pfizer-BioNTech Covid vaccine- 19 was only 40.5% effective in preventing symptomatic disease.

The analysis, which was carried out as the delta variant became the dominant strain in the country, still found that having two doses of the vaccine offered strong protection against serious illness and hospitalization, however reported the country’s health ministry.

Data also appeared to show decreasing efficacy of the Pfizer-BioNTech vaccine, with the vaccine only being 16% effective against symptomatic infections for people who received two doses of the vaccine in January. However, for people who received two doses in April, the efficacy rate (against symptomatic infection) was 79%.

But a study in England from April to May found that after two doses, the Pfizer-BioNTech vaccine was 88% effective against symptomatic disease caused by the delta variant.

Comparing the results is tricky, however, given the differences in the nature of the vaccination programs in the two countries (Israel has given its entire adult population the Pfizer vaccine, for example, while in the UK several vaccines are used. , with the Pfizer-BioNTech injection primarily given to young people) as well as the differences in study dates, Covid testing regimens and age groups.

Like the Israeli data, the English data also concluded that after two doses the Pfizer-BioNTech Covid vaccine is 96% effective against hospitalization of the delta variant. Likewise, he found that the Oxford-AstraZeneca vaccine was 92% effective in preventing hospitalization after two doses. Initial data on vaccine efficacy from clinical trials, published by Pfizer and BioNTech last year, showed the vaccine to be 95% effective.

Professor Lawrence Young, a virologist at the University of Warwick School of Medicine in the UK, told CNBC that cases of Covid in fully vaccinated people are a reminder that “no vaccine is 100% effective” .

“There will always be a proportion of individuals who will remain susceptible to infection and disease,” he said on Monday.

“There are also two other factors that impact the effectiveness of the vaccine: (1) decreased immunity – we still don’t know how long the protective immunity induced by the vaccine lasts. This is most likely a factor in the elderly and the most vulnerable who were vaccinated at the start of the vaccine rollout program, ”he noted.

The second factor, he added, was linked to “breakthrough infections in individuals vaccinated due to the more infectious delta variant” which added weight to the case for booster vaccination programs, he said. he declares. For now, the jury is still out on recall programs with a decision yet to be made in the US and UK

It is difficult to know the full extent of ‘breakthrough’ Covid cases, but figures collected by NBC News revealed that at least 125,000 fully vaccinated Americans have tested positive for Covid and 1,400 of them have died . Still, the 125,682 ‘groundbreaking’ cases in 38 states found by NBC News accounted for less than 0.08% of the 164.2 million (and more) people who have been fully vaccinated since the start of the year, or about one. out of 1,300.

That is, the number of cases and deaths among the vaccinated is very low compared to the number among the unvaccinated. Health officials, especially in the United States, are urging unvaccinated people to come forward for the Covid vaccination.

Andrew Freedman, an infectious disease reader at Cardiff Medical School in the UK, told CNBC “groundbreaking” cases were to be expected.

“Vaccines are very effective in protecting against serious infections, hospitalization and death, but they are less effective in protecting completely against infections and we know that many people who have been fully vaccinated still suffer from delta infections with , in most cases mild symptoms, ”he told CNBC’s“ Squawk Box Europe ”Monday.

“What we don’t know is whether giving an additional booster will actually increase protection and reduce delta-variant infections,” he noted.

It should be noted that studies show that people who are fully vaccinated are much less likely to suffer from a Covid infection – or to contract the virus in the first place.

New research from the UK published last Friday showed that double-vaccinated people were three times less likely than unvaccinated people to test positive for the coronavirus.

Analyzes of PCR test results in study REACT-1 – a major coronavirus surveillance program in Britain led by Imperial College London – also suggested that fully vaccinated people may also be less likely than those who are fully vaccinated. unvaccinated people pass the virus on to others, due to having a lower viral load on average and therefore probably less virus.

Professor Paul Elliott, director of the REACT program at Imperial’s School of Public Health, said the results underscored both the benefits and limitations of Covid vaccines.

“These results confirm our previous data showing that two doses of a vaccine provide good protection against infection. However, we can also see that there is still a risk of infection, as no vaccine is effective at 100%, and we know that some doubly vaccinated people can still get sick with the virus, ”he said.

Steven Riley, professor of infectious disease dynamics at the Imperial, said so-called “breakthrough infections” in fully vaccinated people needed further study, especially as parts of the world face the spread of disease. the delta variant.

“The delta variant is known to be highly infectious, and therefore we can see from our data and others that breakthrough infections are occurring in fully vaccinated people. We need to better understand how fully vaccinated people are. who are infected are infectious because it will help to better predict the situation in the months to come, and our findings contribute to a more complete picture of this situation. “