Ex-WHO Chief Scientist: Third dose of original COVID-19 vaccine is still good against severe disease, death. Watch out for variants of concern

While the world is trying to get back to normal and forget about Covid, one thing that is unpredictable and that could change the status quo is the emergence of one or more variants of concern (VoCs). New variants of the virus will emerge over the next year as they have done in the past three years. The virus is constantly adapting and evolving and each new variant is likely to have an advantage in transmissibility. But a VoC designation (and a corresponding Greek letter from the WHO) will be given only if a variant is better at evading the immune system, causes more severe disease or is much more transmissible than those currently circulating.

What is happening in China now is a repeat of what was seen earlier in 2022 in countries that had minimal transmission of the virus and then lifted restrictions. Because the Chinese have not been exposed to natural infection and vaccine-induced immunity tends to wane, plus a lot of the elderly have not received even primary vaccination let alone booster doses, a large part of the population is vulnerable to infection with Omicron sub-variants. For now, the circulating variants are similar to those seen in other parts of the world. We need to keep a close watch on any emerging concerning variants.

Bivalent vaccines have been reported to be effective for Omicron variants as well. But India does not have them. What should we do then?

While the updated bivalent vaccines, which contain antigens from both the original virus and the Omicron variant, have been shown to be very safe as well as good at stimulating a broad immune response, only mRNA vaccines have so far been approved with this composition. The bivalent vaccines may be marginally superior to the original vaccine when used as a booster but a third dose of the original vaccine also provides a good boost and should be used in all countries where the bivalent vaccines are not available.

Do Indians need a fourth dose of the vaccines they have?

It depends on a number of factors, including the age of the person, the vaccine used, underlying conditions and time that has elapsed since the third vaccination. For people at high risk (such as the elderly, the immune compromised etc), a fourth dose would further boost the immune system and provide more protection against disease (though this is likely to be temporary). More research is needed into the duration of protective immunity as well as the type of vaccine that should be used as a booster. Especially in countries like India, where a nasal vaccine has recently been approved, it is possible that stimulating mucosal immunity may confer benefits like prevention of infection when used as a booster but this needs carefully performed studies.

Do we need an annual booster shot?

Luckily for us, the vaccines that were developed using the original Wuhan strain of the virus, are still good at preventing severe disease and death, even though their effectiveness against infection dropped with the Omicron VOC. However, three doses (two primary and one booster) are needed to mount a broad and sustained immune response. We still do not know whether a yearly booster will be needed, but we do know that immune responses wane over time, especially in older people. A new VoC must spur action to ensure that fully vaccinated people — especially those who are older or immunocompromised — receive booster doses.

What is the trajectory of COVID-19 going forward?

While that is hard to predict, it will gradually settle down into an endemic infection. This does not mean that it will not cause disease or death — last week, the WHO reported 10,000 deaths, a number that is still too high. We need to continue to use all the tools available, including antiviral drugs like Nirmatelavir-Titonavir (PQ has been granted recently to an Indian generic), early diagnosis and supportive treatment. Further, we need to continue to manage our risk by avoiding crowds, staying home when sick, masking in crowded places and improving ventilation of indoor spaces. These precautions will help prevent not only Covid but other respiratory infections as well. Continued surveillance and strategic sequencing of isolated viruses will keep us informed of changes in the virus genome that may have implications for disease management.

What needs to be done to prevent epidemics?

Vaccination remains a key and powerful preventive tool. There is still inequity globally with regard to access to vaccines and this needs to be addressed. In the short term, these countries (9 have <10 per cent and about 50 countries have <40 per cent coverage) need health system support to expand vaccination coverage. In the longer term, health system strengthening, investments in health workforce and laboratory capacity as well as distributed manufacturing and technology transfer will be the key strategies to prevent and respond to epidemics and pandemics.