Once pandemic ends, Covid likely to stay on as endemic
We have just crossed a milestone: one crore of our citizens have been vaccinated for the SARS-CoV-2 coronavirus. Our vaccination campaign started on January 16. This is awesome; one crore vaccinations in a month.
The vaccine recipients are healthcare and frontline workers. They have provided extraordinary service to the infected and toiled to prevent infection. We salute them.
Largely because of their tireless efforts, and a stunningly efficient infection-management system established with great rapidity, 973 of every 1,000 infected have recovered. (Over one crore of our citizens were infected.)
The Union health ministry has said that India’s vaccine coverage now ranks third in the world, after the US and the UK. However, we have also learnt that there is considerable vaccine hesitancy in India.
A major reason for the hesitancy is that the efficacy of one of the two vaccines being administered (Covaxin) is unknown. This vaccine has been proven safe and evokes a good immune response. But how well it actually protects against infection on exposure to the coronavirus, or how well it protects an infected individual against severe disease, is unknown.
The government has ignored appeals to defer the administration of this vaccine until the efficacy results are obtained. The other vaccine (Covishield) being administered here has been shown to have adequate protective efficacy.
With the expansion of the vaccine campaign, the question in every mind is: when will the pandemic end and life return to normal?
To answer this question, we must figure out whether the vaccination campaign is reducing the prevalence of Covid-19 and the spread of infection.
We do not have the relevant data from India to address this issue: the vaccine campaign here started barely a month ago. The best data available now is from Israel.
The vaccines being provided in Israel are not the same as those in India. Further, Israel first vaccinated citizens who were 60 years or older.
Notwithstanding these differences, the data from Israel shows the hospitalisation rate from Covid-19 has dropped from seven per day to one among the 60-plus who have received the required two doses.
This is solid evidence that the jabs are reducing the impact of the pandemic. Similar observations have come from the US.
But are the vaccines blocking the infection or preventing transmission? After you have taken your two doses, will you be able to participate in an adda (chat) sitting close to a group of people without wearing a mask and yet feel assured that you will not contract the infection?
Or, if you were infected
shortly before being vaccinated, will you be able to assure the others in the group that you will not transmit the infection to them?
These assurances are hard to obtain even for the best of vaccines. A notable exception is the measles vaccine, which provides lifelong protection and has eliminated the measles virus from most global regions.
For the SARS-CoV-2 vaccines, the data on infection-blockage and transmission-prevention has not yet been systematically collected. However, there are indications – though not definitive – that the current vaccines can both block infection and reduce transmission to an extent.
Publicly available results of a recent study in Israel, not yet published in a peer-reviewed journal, show that the viral load among those infected even after being vaccinated was significantly lower than that in the unvaccinated. Thus, the benefits of vaccination are palpable.
Are we in a position yet to answer when the pandemic will end and life return to normal? If the coronavirus stops spreading, would we consider that the pandemic has ended and we can lead a normal life?
The virus will stop spreading if it cannot find a group of new persons to infect. This will happen when a large proportion of people in a community gain immunity, by either infection or vaccination, marking the attainment of the so-called herd immunity.
For this coronavirus, the jury is still out on what this proportion should be — possibly no less than two-thirds.
The closer a community gets to attaining herd immunity, the slower will be the spread of the virus. A vaccine, if it blocks infection or prevents transmission, will promote herd immunity. As far as we can tell, no country has yet attained herd immunity. But almost every country seems to be getting closer; life seems to be gaining normalcy.
Will the virus ever be eradicated and the pandemic actually end? It is difficult to predict whether the pandemic — defined as an infection that spreads quickly worldwide or over a wide area and often causes severe disease — will end.
It likely will. But it is unlikely that the virus will ever be eradicated. In the simplest of scenarios, a virus can be eradicated by vaccination if (a) the vaccine evokes such an immune response that the virus cannot escape, and (b) the virus cannot persist in an animal reservoir.
For the SARS-CoV-2 coronavirus, neither of these holds good. Most likely, the coronavirus came to us from bats via pangolins. In addition, the coronavirus infects cats, hamsters, rabbits and minks. And minks can directly transmit it to humans. Thus, there are known animal reservoirs, and the coronavirus may be reintroduced after eradication.
Besides, although the vaccines evoke a high immune response, it is unclear whether they can block infection. Even among people who have had Covid-19, the level of the antibody required to block re-infection — called neutralising antibody — wanes after six to eight months.
The coronavirus infection and the available vaccines produce T cells that kill virus-infected cells and also produce cells that provide immune memory, called B cells.
The B cells are capable of manufacturing antibodies if there is a new infection. But, for none of the available vaccines has it been established that re-infection can be blocked.
The decline of immunity will likely make the coronavirus become endemic to human society. That means the coronavirus will continue to circulate in all human societies. The prevailing antibody levels will ensure that not too many people in any community will be infected during a year, but the number of infections will remain near-constant over many years.
Of concern, however, are genetically altered forms of the coronavirus. These genetic alterations — called mutations — occur naturally and can help the coronavirus infect more efficiently or render it more virulent. As we are now witnessing with the mutant subtypes that have emerged in the UK and South Africa.
These mutants may also escape the immune response produced by the available vaccines. In which case, the available vaccines may often need to be tweaked to control infection.
Tweaking of vaccines is not unknown, the most familiar experience being with the influenza vaccine. The flu virus acquires mutations quite rapidly, and the mutant flu viruses do not respond adequately to the available vaccines. Each year, therefore, a new formulation of the flu vaccine that is effective against the newly arisen mutants has to be found and provided for use.
It appears inevitable that the SARS-CoV-2 coronavirus pandemic will become endemic. But even if the spread of the coronavirus cannot be completely stopped by vaccination, the decline of its spread and prevention of severe disease and death will be significant steps towards regaining normal life.
For endemicity to be established rapidly, vaccination campaigns should be expanded using vaccines of known and high efficacy, and vaccine hesitancy must wane.
⚫ The author is a National Science Chair