The Omicron variant of SARS-CoV-2 clearly appears to be taking over as the dominant strain of the virus, reflecting its increased transmissibility, and ability to escape the immunity conferred by the standard vaccination schedule or past infection. There is evidence to suggest that such immunity, which wanes with time elapsed from the second dose, can be boosted with a third dose of the vaccine.
There are several arguments which are being made against boosters, which seem to be oversimplifying the discourse.
The first of these arguments is that two doses protect against severe disease, irrespective of the waning protection against infection with the passage of time. We now know this is not true. A study analysing data from medical databases in Brazil and Scotland (with close to 2 million adults from Scotland, and 42 million from Brazil) found protection from the vaccine against hospitalisations and death beginning to wane within three months after the second dose. This study analysed data before the Omicron variant was reported. A more transmissible variant would mean a potentially larger denominator of those infected, and even if a small proportion of these individuals need hospitalisation, we could potentially overwhelm the healthcare system. A shorter doubling time which is being reported for Omicron would also mean that infections are likely to be clustered in time, making “flattening the curve” more challenging.
Is it just like a flu?
Second comes the statement, “Omicron could be just like the flu.” We need to remind ourselves that influenza kills 12,000–52,000 individuals in the U.S. every year (as per the Centers for Disease Control and Prevention), and possibly a significantly higher number in India, where we do not routinely test for the virus. We also need to remind ourselves that respiratory infections increase risk of heart attacks and strokes upto sixfold, and it would be in our best interests to prevent them, especially in the elderly and immunocompromised. Even if Omicron intrinsically causes a milder illness than the existing variants, its impact on vulnerable groups could be profound, and cannot be trivialised. Post-COVID sequelae and long-COVID do not often get captured in statistics since they may not be associated with hospitalisation, but are very real reasons for us to do our best to prevent infection. But focusing exclusively on the fact that Omicron may not cause disease as severe as the Delta variant, we ignore all the collateral damage that it might cause which may not get labelled as severe COVID disease.
Effective strategy
Thirdly, the view that boosters are a luxury when India has vaccine shortages: An important question is whether it is hesitancy or shortages that have prevented the entire eligible population from being vaccinated? In addition, when last checked, a majority of the doses presently being administered are second doses to those in the relatively low-risk 18–44 age group category, followed by first doses to individuals in the same category (close to 3.6 million and 0.9 million doses, respectively, of the 6.2 million total doses administered on December 22). Suspending vaccinations temporarily for those under 40 years of age without comorbidities (who, even when unvaccinated, suffer mild illness, the data from South Africa confirming this for Omicron) to offer booster doses to vulnerable groups might be a more effective strategy rather than waiting for a later date after Omicron has spread through the community and caused irreparable damage.
Lastly, a booster with the same vaccine does not work: The COV-BOOST study analysed seven different vaccines as boosters and found all of them effective to varying degrees after two doses of Covishield, including Covishield as a booster. A heterologous prime-boost strategy (booster with a different vaccine) definitely performs better, but whether a third dose of what is available today is better than an ideal third dose that’s available a month later needs to be modelled. Mixing the available vaccines (Covishield followed by Covaxin and vice-versa) is being tested, and if the results are promising, this might be an efficient strategy.
Healthcare workers
Other considerations that must be weighed in the decision to roll out a booster immediately is that we do not want hordes of individuals gathering to receive their third dose in the middle of an Omicron surge, turning vaccination centre gatherings into superspreader events. This is very likely to have happened with the Delta variant during the second surge, and we must not make the mistake of repeating this with Omicron. Rapid, widespread transmission would also mean the possible selection of newer variants, the attributes of which are impossible to predict. We also do not want healthcare workers falling ill at the same time, thereby paralysing healthcare services (it has been close to a year since when frontline workers have been vaccinated).
Our vaccination programme, combined with the high background seroprevalence from past infection, has likely protected us for the last few months. However, it was always known that if there was a new variant which caused vaccine breakthrough infections and reinfections, we could face another big wave. In addition to strictly preventing crowds and superspreader events, we need to act fast, using the available scientific evidence, to prevent such a wave with the Omicron variant. Rolling out booster doses to the immunocompromised, elderly, and frontline workers immediately could be invaluable.
(Lancelot Pinto, MD, is a consultant respirologist with P.D.Hinduja National Hospital and Medical Research Centre, Mumbai, India.)
