A healthcare worker receives a dose of Covishield at a medical centre in Mumbai, January 19, 2021. Photo: Reuters/Francis Mascarenhas
- A study has found that neutralising antibody levels induced by two doses of the AstraZeneca vaccine dropped in the presence of an omicron infection to below the detection threshold.
- The study only considered the protection afforded by antibodies known to wane over time and says nothing about long-term immunity.
- ICMR chief Balram Bhargava said the National Institute of Virology is currently growing copies of the virus and that any studies involving viral particles will be rolled out after.
New Delhi: A study conducted in the UK has found that the AstraZeneca COVID-19 vaccine loses effectiveness to a considerable extent against the omicron variant of the novel coronavirus.
The UK Health Security Agency, formerly called Public Health England, conducted the small study involving 581 cases of the omicron variant and uploaded the results on December 10. It reported that the level of neutralising antibodies induced by two doses of the AstraZeneca vaccine dropped in the presence of an infection by the omicron variant to below the researchers’ minimum detection threshold.
One of this vaccine’s principal manufacturers worldwide is Serum Institute of India, in Pune. Serum Institute also sells the vaccine in India under the name ‘Covishield’, and it accounts for the vast majority of vaccinations against COVID-19 in India.
The study’s researchers tracked cases of the delta variant between November 1 and 27 and those of the omicron variant between November 27 and December 6. Its final analysis had 581 cases of the omicron variant and 56,439 cases of the delta variant.
Now, the UK study’s results have two important considerations.
First, the study only considered the protection afforded by antibodies known to wane over time – i.e. humoral immunity. It says nothing, at the moment, about long-term immunity – i.e. cellular immunity. Studies checking for the potential implications on the latter front are currently underway.
Second, the study’s cohort size of 581 individuals is small because the UK hasn’t recorded relatively many cases involving the omicron cases thus far. The study’s paper also notes that there is a paucity of vaccine effectiveness data vis-à-vis severe disease, hospitalisation and deaths caused by infections of the omicron variant – also because the UK is yet to register such cases.
Note that the primary outcome of COVID-19 vaccines is to prevent severe disease, hospitalisation and death and not to prevent infection. The study is, however, about preventing infection.
In India, studies of COVID-19 vaccines’ effectiveness against the omicron variant are yet to kick off. In response to a question posed by The Wire Science at a press conference in New Delhi on December 10, Indian Council of Medical Research director-general Balram Bhargava said the National Institute of Virology, Pune, is currently growing copies of the virus and that any studies involving viral particles will be rolled out after.
India has thus far recorded 33 cases of the omicron variant.
Aside from the implications for Covishield users, the study could also affect deliberations on booster doses. It found that a combination of two AstraZeneca vaccines (or two Pfizer vaccines) followed by a booster shot of the Pfizer vaccine – administered at the appropriate intervals – was 71% (or 76%) effective against infections of the omicron variant.
India has maintained thus far that there isn’t enough evidence to roll out booster doses.
A study from South Africa, uploaded on December 2, had also found signs that the omicron variant could evade vaccine-induced immunity. And like that study, the UK study also concluded expecting the omicron variant to prompt an increase in the number of reinfections.
“Preliminary analyses indicate approximately three- to eight-fold increased risk of reinfection with the omicron variant.”
In the study itself, 4.9% of participants had had and recovered from COVID-19 before. The interval between a prior infection and reinfection ranged from 88 to 541 days.
It also reported that the secondary attack rate – the chance of an infected person’s contacts getting the infection themselves – was higher for the omicron variant than it was for the delta. In household conditions, it was 10.7% and 21.6% for delta and omicron, respectively. In non-household conditions, it was found to be 3.2% and 3.8% for delta and omicron respectively.
A small study conducted by researchers of the Scottish government, also released on December 10, also reported a case doubling time in Scotland of 2.18-2.66 days due to the omicron variant. At this rate, the researchers wrote, the omicron variant is likely to account for the majority of cases in the country Scotland between mid-December and early January 2022.
This is in line with the UK’s study’s conclusion that the variant will account for most cases in England by mid-December, too.